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In this podcast, I chat with scientist and friend Dr. Bill Campbell all about flexible dieting. Specifically, we discuss a study out of his lab that compared a flexible, IIFYM diet with a more rigid, meal plan approach.

In case you’re not familiar with Dr. Campbell, he’s a professor of Exercise Science and the Director of the Performance & Physique Enhancement Laboratory at the University of South Florida, who’s also published more than 150 scientific papers.

In other words, Dr. Campbell has long been behind the scenes, conducting research on practical, fitness-related matters that can be applied to get us more jacked.

The study we’re discussing on flexible versus rigid dieting is no exception. Surprisingly, it’s the first comparison of IIFYM to rigid dieting with resistance-trained athletes as the subjects, which makes it especially applicable to fitness folks.

In this episode, Dr. Campbell describes the study, the results, and his practical approach of protein-anchored flexible dieting. We also get into incorporating processed versus unprocessed foods in a flexible diet, fiber supplementation, post-diet weight regain, animal versus plant proteins, circadian rhythms, and a lot more. 

So, if you want to learn what the science says about flexible dieting and how it compares to following a meal plan, how processed food affects our eating habits, and how to avoid body fat overshoot after your diet, don’t miss this episode! 


0:00 – My pre-workout Pulse’s seasonal flavors Frosted Cranberry and Apple Cider are 20% off this week only! Go to to check them out and use coupon code MUSCLE to save 20% on any non-sale items or get double reward points!

4:25 – Tell us about your findings on the study of flexible vs. rigid dieting.

10:47 – Would you expect the same results if someone was new to dieting?

19:02 – Will you experience more hunger if you lose more muscle while dieting? 

24:05 – How much fat can I gain in one day?

25:10 – When is it appropriate to take a rigid approach vs taking a flexible approach?

30:36 –  How do we choose the right foods to hit our macros?

42:10 – What is your theory on eating around your circadian rhythm?

49:45 – What are your thoughts on supplementing with fiber?

52:20 – Is there anything else you would like to add? 

53:41 – What is the best source of protein?

57:51 – Where can we find you and work?

Mentioned on the Show:

My pre-workout Pulse’s seasonal flavors Frosted Cranberry and Apple Cider are 20% off this week only! Go to to check them out and use coupon code MUSCLE to save 20% on any non-sale items or get double reward points!

Bill Campbell’s Instagram

What did you think of this episode? Have anything else to share? Let me know in the comments below!


Mike: Hey there, and welcome to another episode of Muscle for Life. I’m Mike Matthews. Thank you for joining me today for my chat with scientist and buddy, Dr. Bill Campbell on flexible dieting and specifically some new research on flexible dieting that came out of his lab and research that was done with resistance trained athletes as the subjects, which is cool because that means that it is especially applicable to US Fitness folks.

And in this interview, Dr. Campbell explains how this study was done. He explains the results and then he gets into practical takeaways. And specifically, he talks about something that he likes to call protein anchored, flexible dieting, and he also talks about processed versus unprocessed foods and how to best incorporate those in a flexible diet plan.

Fiber supplementation, post diet, weight gain, animal versus plant protein, circadian rhythms and more. And in case you are not familiar with Dr. Campbell, he is a professor of Exercise science and the director of the Performance and Physique Enhancement Laboratory at the University of South Florida. And he has published over 150.

Papers. So if you wanna learn what the science says about flexible dieting versus more rigid dieting and how it compares to say, following a set meal plan. And if you also wanna learn about how processed food affects our eating habits and how to avoid gaining too much body fat after a diet, this episode’s for you.

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Order now. Use the coupon code muscle save 20%. Try Pulse risk free and see what you think. Hey Bill, welcome back, uh, to my podcast. 

Bill: Yeah, thank you for having me on again. 

Mike: Yeah. Yeah. I’m looking forward to today’s discussion, which is going to be about, uh, some research, well, we’ll start with some research you did on flexible versus rigid dieting and always, uh, always in a topic of discussion.

And so why don’t we start there? Can you tell us about this, this study that you did, what was unique about it and what some of the interesting, what your thoughts are on, on the findings? And then, um, from there, we know where we’re going, but people listening, you’ll find out . 

Bill: Yes. Yeah. I’d love to talk about the research that we do and, and whenever I talk about this study, I have to start with my former student, Lauren Conlan.

She runs a coaching company called Team Loco Fit. So this was her brainchild. She coordinated the entire study. This was kind of her passion as she was a young coach at the time. That we did this. So I need to give her, um, a lot of the credit for, for, for all of the credit for making it happen. Again, it was her brainchild and there was no research at the time, and I don’t think there, I think this was the only study looking at flexible dieting in a resistance training population.

I, I think that’s still the case. And, 

Mike: and that’s an important point, right? Because, uh, if, if you look into the literature, um, for, for other studies on flexible dieting, they, they are in the, in the obesity literature mostly. And you’re looking at a lot of people who, uh, are not in necessarily the same situation or, or the circumstances of physical circumstances.

Lifestyle circumstances are very different than many of the people. Listening. For example, 

Bill: if you, yeah, if you’re a fit person and you do flexible dieting, the study is, can be perfectly extrapolated to you. Cuz that was the population that we, that we looked at. So our goal here was two things. We wanted to do a diet, so we wanted to compare a flexible diet versus a rigid diet.

And I’ll explain how we implemented that. So we did that for a 10 week period, but Lauren also wanted to look at what happens when the diet is over. So we had a 10 week diet phase, and then we had a 10 week post diet phase. That phase was where the subjects could do whatever they wanted. They, there was no restrictions on what they were allowed to do during that post diet phase.

But let’s, let’s start with just talking about the diet phase, cuz that was the, at least from my perspective, that was the, the main thing, can you implement a flexible dieting approach? And as long as the calories are the same to eating the same foods all the time, do you get the same, the same outcome? So that was the main question.

And for the flexible diet. Group, we, we did what everybody does. We said, here’s your macros. Your you, you have to eat X no more than this. Many of carbs, this amount of protein, this amount of fat. And we based their macros on their, what they normally ate at baseline. So we took those calories, we reduced them by 25%.

It was either 20 or 25, I don’t remember. It might have been 20, but 20 or 25% lower than baseline. And the other requirement that we had was, we also need you to hit a specific protein goal. And that was two grand, two grams of protein per kilogram of body mass. So probably something like pretty standard nine grams per pound.

So that was the flexible diet. N never mentioned anything about food choices, uh, food groups. There was nothing 

Mike: mentioned. So it was on them to make their meal plan and to report compliance and so forth? 

Bill: Yes, and, and that’s an important thing. We also, obviously we had to educate them. We gave them a book on flexible dieting.

So he, Lee had a book, I don’t think I was aware of your book at the time, um, with all of your menus, food options. So we, we gave them education in case they weren’t currently doing that cause they were randomized to their groups. The other group, what we called the rigid group, we had a registered dietician give them a specific diet.

Now there were a few choices. Very, very limited. Um, so they were given. A meal plan where they said, here’s your breakfast, here’s your lunch, here’s your dinner. Um, hey, I don’t like chicken breasts. Can I eat lean beef? Yes, here’s that plan, but really limited. Um, you know, broccoli for cauliflower, you know, something to that effect.

So, yep. A rigid diet. That was a plan written by a registered dietician. Same caloric deficit, 2020 5%. I don’t remember specifically. And we also made sure their diets would, would give them two grams of protein. So calories were controlled, but we standardized it for protein. Yep. All of the subjects were resistance training.

And this was the first study that we actually did not supervise their workouts in my lab. So this was on their own. And we told them, just don’t change what. Doing. The only change we want is your, the diet that you’re gonna follow, whether it’s the, the flexible or the rigid, rigid diet. Yep. So whatever training they had their log, all of their training, if they were doing cardio, we said keep doing that.

Just log it. So tell us, you know, how much time you’re spending doing each of these things. But we didn’t control that part as well as what I, what we normally do. So that diet phase went on for 10 weeks, and at the end of the 10 weeks of dieting, what we found was that there was no significant differences between a flexible diet or a rigid diet.

Approximately the same amount of body weight loss, approximately the same amount of body fat loss, approximately the same retention of lean body mass. So the, my overall conclusion, at least during this diet phase was, you know, it really doesn’t matter. If you have a follow a meal plan or you follow a flexible dieting approach, as long as you’re in a deficit, you’re going to get the, the benefits of that deficit.

Mike: Now that though assumes that cuz you dealing with more experienced people worked to, to the benefit of this study, right? Because these are people, um, w would you, would you think that, let’s say if somebody were new to all of this, would you expect that tho those results, like if, if you’re dealing with people who are kind of used to meal planning, for example, um, then I, I would, I would assume that those findings are, are not surprising.

Um, but what are your thoughts, uh, about people maybe who are less experienced with dieting or, or was this approach new to, to a fair amount of these people? 

Bill: No, we, we had some people that. , like tracking their macros. And they were randomized to the group and we, and you know, and, and we said, listen, if you’re going to do this study and you know, you can’t lie to us like you, you have to stop tracking your macros and eat these foods that we’re gonna, you know, that we’re going to, that we’re gonna give you on this menu.

Yeah. And likewise, we had people who didn’t track their macros that we had to teach. Here’s how you do this.

I don’t know. I mean, I know personally if I’m working with a client and they’ve never, they’re very new to dieting, I would not start with flexible dieting. I think that’s more of an educated approach. 

Mike: Yeah. Um, I think a little bit, it just, it just requires a little bit more. And, and that’s why I asked that cuz I’ve had that experience, um, speaking with and working with many, many people over the years who are very new to this kind of stuff.

A lot of those people, they read a book of mine, for example. That’s the first time they’ve ever even heard the term energy balance or they’ve ever even heard the term macronutrient. And, uh, uh, a lot of, a lot of them are a little bit intimidated by the process or even if they, and. Almost all of the time, they, they’ve done a good job, actually.

They’ll reach out to me sometimes, like, Hey, this meal plan, it, it, it checks all the boxes, but I’m just not sure because really, do you, I really can eat this many carbs, or I really can have, uh, , I can have, you know, 20 grams of sugar, added sugar every day. That’s okay. Really? And so, so sometimes, yeah, people, they, they prefer a little bit more structure initially, uh, because in it takes, let’s just say it, it takes out, um, some of the, some of the margin for error, you know?

Bill: Yes. Yeah. So, yeah, we, we didn’t have that luxury though in this study. Whatever they were assigned to is what they had to do. We didn’t work with them. How we would if they were clients. And that’s always gonna be the case with research. Um, that, but we did have education. We did train the people who needed to be trained, um, on how to track their macros.


Mike: I wouldn’t consider that a limitation in the study. I mean, even the fact that you didn’t control the, the exercise has a benefit in that you were controlling the diet and seeing how that might impact. Like, it would’ve been interesting if in one group or the other they started doing less exercise, just they missed more cardio sessions or training sessions.

Like that would’ve been an interesting observation. Right. And similarly, it’s, it’s, I think it’s a, it’s probably a strength in the study that you had. Who are macro trackers and who are not macro trackers. And the macro trackers had to stop tracking their macros and the, the non macro trackers had to start tracking, which again, I think is, is very representative of, uh, people who, uh, a lot of people who are, who are listening, even people who are new to all this, where they’ve gotten a little bit of education, uh, but they are, are new to the implementation.


Bill: Yeah. And we had a really, the subject in this study, the dropout rate wasn’t high. Now again, they didn’t have to come to my lap, the train four, five days per week. So that, I’m sure that helped. The other thing about the phase was, And you’ll, you’ll love this. This is kind of, I think, what defines you in your approach.

Almost all of the body weight that was lost was from fat mass. It was, it was a really good outcome. I mean, it was, uh, over, well over 90% of, of the weight that was lost. Now we, that was also before I had a machine to measure total body water. So we al I always like to find that out now, but I didn’t have that then.

But, and again, 

Mike: I guess it, because then even the, the lean mass lost. Well, how much of it was really lean 

Bill: mass? Yes. Yep. Yeah. Right. , but we did everything that you would ex the things that we know. Again, my lab kind of specializes in this. We know the way that you do that is to resistance train when you’re dieting, to eat a higher pain diet and obviously be consistent with all of those things.

So that study, they did that and it was, it was, it was awesome just to see how the composition of the weight loss was so high in body fat. It was, I mean, it’s almost like the standard study now in my lab. If we can reach that study and we, we’ve done something good for 

Mike: our subjects. Yeah. That’s great. And, and for people listening, this is something it just makes me think of, cause I get asked fairly often.

People ask me, how do I know if I’m losing lean mass? Or is it just less water or less glycogen as I’m dieting? And so my, if anybody listening, if, if you’ve wondered that my, my standard response is, well, one, you can look at your performance if you’re retaining most or all of your performance in terms of strength, um, or, or muscle endurance even.

Um, but primarily strength. You’re not losing any lean mass to speak of. Uh, just it’s, it’s, if you’re losing a fair amount of muscle, you’re also gonna lose strength. You’re, you’re gonna see your one RMS go down, for example. And that also then informs how you should be training. I always recommend people to keep training heavy, keep training hard, keep trying to make progress.

Even if, you know, you’re not gonna make progress after maybe three or four weeks of dieting, but have the mentality, get in there, try to beat your last workout by one rep. Like, don’t, don’t, don’t just, uh, phone it in or walk through your training because, oh, well I’m cutting and it’s not possible to make progress.

Keep training hard. And then also understand that any lean mask that you do lose, if you’re gonna lose any, you’re gonna gain back very quickly when you bring your calories back up to maintenance. So don’t, don’t sweat it. So if you are seeing, it’s been, I. I haven’t, I haven’t done an extended cut in some time.

I’ve been maintaining for a while. But for me personally, especially when I’ve gone from lean to very lean, after about six weeks or so, uh, yeah, probably about six weeks, I will, I will lose, uh, a couple of reps on my bench press. I’ll notice that I might even have to go down five pounds to, to hit my six reps or eight or four or whatever I’m doing based on my training.

Um, I’ll usually lose a rep or two on my squat and deadlift, and that’s, that’s with, you know, good compliance and good recovery and doing everything I can. And it, I still, I still lose a little bit if I’m cutting for a long enough period. But again, I’m not concerned because I know that right when I go back into maintenance and I’ve experienced it enough and, and so I just recommend people to, to.

Know that it’s okay because if you do lose anything, muscle memory is a real thing and it’s gonna come back really quickly. So just do your best, train as hard as you can, and don’t, uh, don’t get too worried about, oh, well I, you know, I, I was curling 40 fives when I started. Now it’s forties. Oh, no, . 

Bill: Yeah.

That’s, that is something that a lot of people, and again, I, I’m, I’m one of the, the big voices of pr protect muscle, protect muscle landing, plan your entire diet so that you protect muscle. I mean, obviously prioritize fat loss, but you do gain it. Let’s just like you said, and I think a lot of people fail to appreciate it.

Whatever you lost, you’re gonna get back. Within a few weeks. Now that doesn’t mean don’t take it seriously to try to keep it because there’s, you know, there’s this, um, protein stat theory that suggests that your hunger levels are gonna be significantly higher if you’ve lost muscle mass after a diet. Um, also if you do lose it and then you get it back, let’s say even in a month, well now that’s two, three months of not gaining any new muscle.

So I, I don’t wanna minimize it, but I wanna comfort people who do lose some muscle. It’s not gone forever. It will come back. 

Mike: Absolutely. And can you talk a little bit more about what you just mentioned, uh, that if, if you lose, um, muscle while dieting, that there is a. is the likelihood that you’re gonna experience more hunger after?

Bill: Yeah, there’s, there’s, uh, I would say at this point it’s, it’s in, it’s a theory, but, um, it’s been shown with these near or literal starvation studies. So the Minnesota Starvation Experiment, um, Dou was another author who reanalyzed that data. There was another study in, um, army Rangers. They were in a thousand calorie caloric deficit for like eight weeks or seven.

Yeah, I remember that paper. Yeah. Yeah. So those are two studies. Um, That, that I’m just naming off the top of my head, where after their severe caloric deficits, when they were allowed to go back to eating what they would normally eat, so there was no more restrictions on them. The prevailing, prevailing thought at the time was, you’re gonna have hyperphasia this, this really strong desire to eat, let’s just say like an uncontrolled sensation of hunger that’s gonna persist until your body levels that you lost come back to what they were before you started dieting.

But in these two studies where they actually went in and they analyzed this, their, their, their elevated hunger drive, and again, elevated to the, to a very high level because it was such a crash. That stayed high, well past the point when they had already gained and then gained additional body fat than what they started their diet with.

And it remained high in both studies until they regained their fat-free mass, let’s just say muscle mass that they, that they lost during their diets until that went back to their baseline levels. That’s how long this hyperphagia lasted. So I use that, and that’s kind of, you know, one of the theories that we embrace for our research.

We, we wanna protect muscle because hunger’s what? Hunger’s the, the deciding factor. You, you might be hunger for a day or for a meal, but you’re gonna lose the hunger. Eventually. Yep. So we wanna 

Mike: set up, it’s a, it’s a, it’s a war of attrition that you just can’t win . Yes, 

Bill: yes. Yeah. So that’s why we have such an emphasis on protect muscle mass when dieting, cuz when the diet’s over, we want you to be set up for success, to maintain your, your progress.

And again, if, if we lost muscle mass or if we didn’t care about that, um, and we only looked at the scale weight, we just set you up for likely failure to maintain your, whatever progress you made with your fat 

Mike: loss. , especially if you continue whatever it is that led to the, to that loss of muscle. Like for example, let’s say just not eating enough protein.

I’ve come across that dealing with a lot of people. I’ve seen it with a lot of, uh, well, a fair amount of women who were not, they just, they never ate a lot of protein and it was hard for them to get used to that. And so they just ended up not eating enough protein. And of course that can, uh, exacerbate muscle loss.

And then I’ve seen it in a lot of GU especially. Guys who are naturally, um, smaller, who naturally have a, a, a lower appetite. And so, you know, I can think of guys I’ve, I’ve heard from over the years where they, they just tend to, they don’t eat that much food. They get, they get full easily. So protein is especially, uh, satiating for them.

And then on the weekends they’re like sleeping in and forgetting to eat meals. And, and that of course, then just brings calories and protein even lower. And so if those people continued that, for example, let’s say now they’re out of their diet phase. They’re, they’re, they’re trying to now normalize their body weight, but they still are not eating enough protein to really support, at least to, to, um, to maximize muscle growth.

Then theoretically, um, they, they, they, they might end up with more body fat by the time. They actually get back to their, their pre diet, uh, musculature, right? 

Bill: Yeah. We call that fat overshoot in, in the, the weight loss literature. And it’s, I used to be a, a personal trainer and some of my clients would go on cruises.

It, that would happen constantly with the, the crew 

Mike: buffets and alcohol. That’s, uh, 

Bill: yes. But a lot of dieting going into their cruise, to I, you know, and then coming back , I just, it made, I was a young profe, you know, trainer. That’s what I did full-time when I, and forever made an impression on me. I’m like, wow.

The body can really gain weight after a diet if you, especially if if you go on a 

Mike: cruise. Yeah. If you, if you give it enough high fat food and enough alcohol, , uh, you can, you can quickly find out the answer to another question that I, that I get sometimes, which is, how much fat can I gain in one day if I really tried

It’s a fair amount. It’s not five pounds, but, uh, it’s, my conclusion was probably about a pound or two a day is probably doable. 

Bill: Well, I think the best methodology to test that would be to take a whatever body fat assessment tool and put ’em on these cruise ships. Cuz that’s where it’s gonna . That’s where it’s gonna happen.

Mike: there, there’s an idea for a study. That could be a fun one. Free cruise, but there , you’re, you’re, you’re gonna, you’re gonna have to, you’re gonna have to eat and drink a lot though. That’s the caveat. So as long as you’re okay with that, then free cruise. If you like what I’m doing here on the podcast and elsewhere, definitely check out my sports nutrition company Legion, which thanks to the support of many people like you, is the leading brand of all natural sports supplements in the world.

Coming back to this flexible versus rigid diving, so, so what are your thoughts then, for people listening, wondering which, which approach should they use or which circumstances do you think it would make more sense to take a flexible approach versus a more rigid approach? And that could just be personal preferences or more objective, you know, what are we trying to accomplish here?


Bill: so I, I’ll, I’ll end from two perspectives. One, I have a bias here, and then the other one is just how I would work with clients. So I think if I’m starting with somebody who’s very naive to food, I wouldn’t, I, we’ve talked about this a little, few minutes ago. I wouldn’t say, yep, here’s your flexible dieting plan.

Hit these macros. I think that’s way too advanced. You’re, you’re throwing ’em into the deep end of the pool. It would be, I, I would start with a meal plan of sorts, but even before that, I would just have them not change anything. Just write down what you normally do. Just just become aware of when you’re hungry.

What foods do you eat? And then over time, uh, you know, I would, I would use their list of foods and say, Hey, you, you know, you had seven cookies in, in one serving of vegetables this day. Let, let’s, let’s do a four too. Let’s go four cookies and two servings of vegetables, and let’s just, you know, let’s just make little changes not changing again.

What I love about that approach, nobody’s changing what they’re eating. They’ve already chosen these foods naturally, and then over time, Uh, I would have, I would teach them, Hey, let’s track your, your, your breakfast macros. You know, let’s, let’s just see how much protein, carbs, and fat you’re getting at breakfast.

Because now what they’re learning is, oh, food has macros. And, and of course I believe macros matter, um, especially for trying to build muscle mass. So I, I would do a gradual approach, but my bias is, I’m, I’m a flexible dieter. It’s kind of how I structure my lifestyle. And I think everybody who eats should, should follow a flexible dieting plan for six months of their life.

If they hate it, leave it forever, but you can’t unlearn. The ed, the food education that you will get from flexible dieting, you’ll butter is fat. You’ll know that broccoli is carbs. You’ll know that salmon is fat and protein. I love, as an educator, I think it is the best. Like I think they sh they’re gonna mandate.

Some things in schools mandate flexible dieting for the students for a month or, or a semester . Yeah. 


Mike: at least, at least teach it, please. Yes. It’s, uh, and, and, and yeah, it, it is, uh, I, I would say, and, and this is, this is of course no surprise to you, but, but for people listening that consistently, the best.

Intuitive eaters, so to speak. The, the people who are able to not follow any set meal plan, who are able to, maybe they would say, eyeball their macros, who are able to eat freely and flexibly and, uh, achieve their body composition goals. And maybe that’s just to maintain, for example, they, they have a lot of experience with flexible dieting as you’ve described it.

They’ve also followed almost always, they’ve followed, they’ve done the rigid approach, they’ve done the flexible approach. They’ve done it in different ways too. Um, for example, they have made, uh, a meal plan of all the foods that they like to eat and just follow that. And then they’ll make swaps here and there.

Or they’ve gone the tracking route where there really are no. Fixed meals other than they know they’re gonna have maybe a protein shake here, they’re one or two or three a day, but then it’s, it, it’s, what do I want to eat for, for breakfast? And then they’re looking things up. They’ve done that. And, uh, it, it, another, another big benefit of of that is that you, you get an intuitive understanding of portion control, uh, of what, proper portions of the foods you like to eat look like.

And, and then that’s very, very helpful. Again, in if you want to get away from all of this and you want to be as flexible as you possibly can while. Controlling your calories and controlling your protein according to your body composition goals. Right? It’s, it’s nice to know that, oh, a serving of, of oatmeal, because I’ve just, and, and it happens.

What’s great is it happens whether subconsciously really, you just get, you get so used to eating certain portions of food and you understand when you look at that, uh, cup of, of oatmeal, you can’t help. But no, if you’ve done enough of this that, oh, that’s like 50 grams of carbs. All right, cool. You know?

Yep. And, and so, um, Going from, going from from there, uh, to the, I think the next, uh, the next, the next thing we want to touch on here is, okay, so if we just need to, to hit our macros and, and that allows us to hit our calories and we want to pay particular attention to protein because, um, that, that benefits our body composition the most and our appetite and so forth.

What about then the, the foods that we choose? If it fits your macros, remember that was a big thing. Years ago when, um, at least in, in the evidence-based space, this was gaining more popularity. And so then people were realizing, quote unquote, that they could eat a box of Pop Tarts every day, so long as it hits their Mac.

That’s all of their carbs. And like, you know, 50% of their fat is just from junk food. As long as they hit their protein in their calories, they’re losing fat or they’re gaining muscle. Oh my God, this is amazing. And so, so what are your thoughts, uh, about, I mean, we could start with that, but then, but then even, even, let’s say more reasonable versions of that where, um, you know, I, I.

I come across a lot of people who they would say they, they eat pretty well. But then if you ask, okay, so like how many servings of vegetables do you eat every day? And, well, maybe like one on average. Okay. So are there some days when you eat no vegetables? Well, yeah. You know, some days I, uh, I don’t really like vegetables, so I, I do it here and there, uh, and, but, but I’m hitting my calories and my macros.

Bill: Yeah. I, I think that’s where a, a large segment of the population in the flexible dieting world, or if the, if you’re gonna call it, if it fits your macros, the mind will wander, well, how much crap can I eat and still make this work for me? and we have research now. There was a, this, the, the best design study in terms of a, a metabolic ward or, you know, living in a facility type of study, which does lack some temptations and ecological validity.

But if you’re gonna get at the just the core question, those are the best studies. This was, uh, done by Kevin Hall. I, I guess he’s probably the, the premier obesity researcher. So there, he kind of answered the question, well, how much can I eat of, let’s just say unhealthy foods or the let’s processed foods.

I mean, that’s usually what most people think of. So like potato chips, um, birthday cake, um, ice cream, you know, all of candy, all of that stuff. Yeah. 

Mike: Cookies. Just tasty stuff. Yes. 

Bill: Yes. So what they did in this study, and I, and I’ll tie this back into our, our flexible dining discussion, but they had people living in this facility, this metabolic ward for a month.

The, and these were non-trained people, so these were just average people, moderately overweight, but not obese. And this was not a weight loss study. So they told the subjects, you’re not here to lose weight. You’re not here to gain. When you’re here and we’re gonna put you on a ultra processed food diet for two weeks, and then we’re gonna follow that up with two weeks of a pro, um, non-processed food diet.

And that was for half the subjects. The other half, they reversed that. So the other half. With non-processed foods and then did two weeks of ultra processed foods. And the amazing thing about this study, not only did they have that, that distinction, unprocessed versus ultra processed, but the calories were matched for carbs, protein, fats, sodium fiber.

I, I mean, I don’t know how you do that, cuz you know that that took a lot of planning. Yeah, I, I, I would have to assume a small army of dieticians to, to, yeah. To standardize all of those things. Um, so they had breakfast options, lunch options, um, snacks, you know, whole, whole more whole foods snacks versus ultra processed food snacks.

And what they found was, When the subjects in the way that was presented to them was, here’s your lunch. Eat as much of this as you want. If you want more, tell us. We’ll bring you another serving of lunch. Or if you can’t eat at all, that’s fine, just put it away. So they were presented with breakfast, lunch, dinner, and monitored how much or how little they wanted to eat.

Snacks were whenever they wanted them. And during the two weeks, the group, when they were on the ultra processed food diet, they actually ate five, approximately 500 more calories per day. So they overate when they were on a processed food diet and that equated to about two pounds or a kilogram of body weight gain over those two weeks.

So I’ll, I’ll take this back to, this was not a weight loss study. The way that I interpret that is if you’re dieting. Can you eat ultra processed foods and still lose body fat? I, I think the answer is yes, but that comes with a cost of being a lot more hungry because the, the, the ultra processed foods, you’re gonna have to eat more of them to get the same level of fullness.

And that’s also what that study showed was the same. But the reason it was the same was because they had to eat 500 more calories, or essentially 20% more food to make, to, to satisfy that hunger where it would equal the same hunger with 500 

Mike: calories less. And, and, sorry, just to make sure I heard you correctly, it was the highly processed group that ate more on average, right?


Bill: Yep. Yeah. Okay, good. Yeah. The high processed food, they ate more calorie. and they gain more body weight. Yes. 

Mike: Yep. Yep. And then coming back to your, to the point you just made, uh, yes, I think that that makes a lot of sense. That also is exactly in line with what I’ve seen, again, working with many people over the years.

And, and many people have reached out to me, um, just to share that they’ve learned that lesson that they, they, uh, to, to use the internet phrase, they fucked around and they found out , where they, they got a little bit too cavalier with their meal planning. And then they realized that, uh, after you know it, it’s, it’s 11:00 AM and they only have 500 calories left for the rest of the day.

Ah, and , they realize, oh wait, this is not gonna be good. And as, as we mentioned earlier, You can’t beat hunger. It, it’s like time. You know? You just can’t, you can’t beat it in the end. Time wins. It beats us all. And, and hunger is, is the diet killer. And even, even in people who are hyper disciplined and who think that they can do it because they’re not weak like everybody else.

Yeah, let’s . I 

Bill: can’t think of too many. Worse scenarios than if I only had 500 calories, then I have a lot of the day to live like that. I always try to reverse engineer that so I can look forward to more food intake . 

Mike: That’s funny. I do the same thing. Is there a reason, is that just something that you just happen to prefer or did it occur to you as, uh, a good thing to try out and then you ended up liking it?

Yeah, I, 

Bill: I would say for many years I probably like you, you, you read the importance of breakfast, like you gotta eat breakfast. So for many years I would force feed myself breakfast and then at some point while I was a professor, I realized I’m not hungry in the morning. Why? Why am I eating these, you know, all these calories?

When I should be utilizing them for when I, when I have a, a higher natural hunger drive around one or two. So I, I would say it was just through the process of personal experimentation that I came to that, um, and yeah, I, I, I, I realized I don’t need to eat breakfast. In fact, I focus better, like I haven’t.

Yep. Actually that’s not true. I, I did, um, I had a small, um, snack earlier, but typically I don’t eat till 10, 10 o’clock, one o’clock. Um, and again, what I really like about that is my focus. It’s, I’m, I’m much more laser focused. 

Mike: I, I noticed the same thing. I eat light throughout the day. Like my breakfast is, I have a scoop of protein with, uh, with Genesis, with my green supplement.

Um, which, which by the way, it’s not a, a powdered vegetable supplement, which I. I’m gonna, I’m gonna, I’m gonna create, I’m gonna create, I’m gonna do this, I’m gonna create a section over, at, over at Legion’s, uh, website. I’m gonna, it’s probably gonna be in the store of stuff we don’t sell, and I’m gonna explain why.

And so BCAs are gonna be in there, eaas hydration supplement that’s gonna be in there. Uh, powdered fruit and vegetable supplement is not going to be in there. It’s my, my green supplement is green because it has spirulina, but I don’t know what else to call it. Even though like many people, they think of these things as green supplements.

Uh, but, but many green supplements are just powdered fruits and vegetables, which I, I don’t sell because I don’t think those are useful. I’d rather people eat their fruits and vegetables. And of course, how the powdered fruits and vegetables are often sold is, well, you don’t need to eat or it’s, it’s good to eat them, but if you, if you.

Like them or you just can’t quite get enough in. You could just take this. I’m not, I don’t agree with that. But anyway, my breakfast is protein powder, scoop of protein powder, scoop of this green. And then, um, I’ll have something light before I train. So when we get done here, I’ll eat some fruit. Um, probably have another scoop of protein powder.

Then at three I’ll have a salad. I do a big salad. I’ll throw some chicken or some beef into some sort of, maybe some fish, some sort of protein in the, in that have, uh, some more fruit maybe, or have like a little bowl of soup with it. Um, I like soup also just to feel full. And then I’ll have, uh, dinner around six or so I’ll have some more fruit and then I make a big pot of vegetables, put some meat into it, and then a couple of hours after dinner, I like to do oatmeal.

I’ll do like a, a. Scoop of, uh, dry oatmeal, throw some nuts. I’ll cook it obviously, but it’s a scoop dry. Throw some nuts in it, throw some fruit in it, cook it up, eat it. And there might be, you know, I’ll eat some dark chocolate here and there, and there might be another little, couple random things thrown in.

But that’s how I like to eat. And I find that this point of focus, you know, basically all my work requires thinking I’m either doing interviews or I’m writing stuff or working on legion marketing things or whatever. And I, I find that by eating light like that, um, I just don’t ever get. Kind of lethargic, all right, time to slow down and digest all this food kind of feeling that I get if I eat a larger meal.

So, for anybody listening, if, if you also, um, if you need, if you need your mind as as as much as you can get it, uh, for, for your, uh, work or whatever you’re doing in the day and you’re not that hungry throughout the day, um, there’s nothing wrong with shifting a lot of your calories toward later in the day.

People will ask me sometimes, well, is that okay? Do, do you not gain weight? Or is, is it not more conducive to fat gain if you’re eating most of your, or at least a large chunk of your daily calories at night, like, I’ll eat my oatmeal at 9:00 PM some nights or nine 30 and, um, Nope. That doesn’t, that doesn’t matter.

So long as your, your numbers are where they need to be when you eat, doesn’t have any impact on body composition, right? 

Bill: Not that I’m aware of. Now, of course, I’m constantly reminded on Instagram. What about eating around your circadian rhythms? And I just feel like that’s very theoretical at this point.


Mike: do you wanna, you wanna talk a little bit about that? You wanna share what’s the, what is the theory? I, 

Bill: I don’t have not, I have not investigated this, so I, I’ve have a conversation, but this is not something that I’ve done research on. Sure. Um, yeah. The way I understand it is you, you somehow learn what you’re circadian rhythm are when your hormones get higher for yourself, and then you, you time your food around that.

Mike: For what purpose? What are we go, what are we getting at? I think, 

Bill: um, well, I’m gonna say what’s told to me is for everything, like if you’re not doing this, you’re, you’re harming your health. You’re making yourself more fatigued, you’re accumulating body. . And again, I, I’m just not aware of researching humans.

That’s why I say I think it’s, I, I don’t wanna say that there’s nothing to it. I, I, I don’t know. I just know that I haven’t been able to find research, like on our flexible dieting study where they had one group of people eat around their circadian rhythms and another group not, and did they gain fat?

Did they control for everything? So that’s why I think it’s more theoretical. Um, 

Mike: that I, I made a note on that, that, that, that’s new to me. I haven’t heard that claim. I mean, it’s immediately refuted though by I would say the entire body of, of evidence that we do have on, uh, using calorie restriction, using high protein intake to improve body composition.

And then all of the anecdotal evidence of people who succeed with that approach, uh, without any instructions about when to eat. I guess the counter arguing could be, well, yeah, you can succeed with that, but you, you don’t know the harm that you’re causing unless you’re getting these special tests done, or your results could be so much better.

Um, okay, but it, let’s just say, based on my experience, if I had to make the bet right now, um, I’m gonna bet against that theory. Maybe, maybe, maybe it’s not entirely right, but maybe there is some validity in some of the assumptions. I don’t know. Yeah, 

Bill: there may be, but I just, there’s not, there’s not empirical research that we can do at this point.

Now, in, like I said earlier, I, I kind of time my food with my hunger much more than I used to. Is that, is, is that my hunger rhythms? I don’t know, but if, if that’s what it is, well, I’m doing that and, and that makes sense 

Mike: to. Yeah, that, that just of course makes fundamental biological sense. I, I don’t think that means that eating when you’re not hungry is bad, of course, for anybody.

You know, cuz some people I know who reach out to me, they, they have to eat at certain times because of how their day is set up. And they would, they would like it to be different, but it just, it, it has to be what it is for now. And, um, that might include eating when they’re not hungry, for example. And that’s not, maybe not ideal because they have to experience more hunger than they would like to experience.

They would like to shift things around, but they’ll ask me, is that okay? Is that bad? I don’t know of any reason to, to think that it’s bad or that you’re harming yourself. Um, it’s just better if, if you can. When you’re hungry, . And if you can set up, I think, your meal composition to reflect that. So again, coming back to kind of a theme of, of what we’ve been talking about regarding hunger is not that there’s anything wrong with feeling hungry, and when we’re dieting, we’re gonna feel hungry a little bit here and there probably.

But, um, if we never feel hungry at all, that’s, that’s the best place to be. Even if it’s not attainable, we want to get to as close to that as we can. Right? Yeah. 

Bill: That, that, to me, that’s heaven, , . 

Mike: Maybe, maybe that’s part of, uh, part of heaven is you’re never hungry, . That’s one, that’s gonna be one of the, one of the perks.

Bill: Yeah. And, and then just to also circle back to another way that I would handle the, the question, well, I can eat all of these, um, you know, processed foods and still make it work. I what I am, what I. Implement, or what I advocate is what I call a protein anchored, flexible eating lifestyle. And what alls that means is we set a protein goal that’s relatively high, I don’t know, a gram per pound, um, 0.75 grams per pound, whatever somebody can comfortably do.

And what that does well, one that, that supports your, your, your body composition goals, assuming that you wanna have more muscle mass, you’re trying to build and maintain your muscle. But by increasing that protein, that also, for lack of a better word, eliminates some choices that you can make. Uh, what I like about this though, there’s nothing that would be off limits for that person, even with a high protein intake.

But it does prevent a, a litany of highly processed food choices. You can’t do that and hit a high protein goal. Because how many highly processed foods are really high in protein? I can’t think of many. Yep. So another 

Mike: strategy. And so, and, and so obviously you’re limited by your calories too, right? Yes. So it’s calories in protein.

So if anybody listening, if you start poking around in a food database, you’ll see what Bill’s saying. It’s, it’s almost impossible, uh, to, to keep your calories where they need to be and to hit your protein if you’re eating too much junk. Yeah. And 

Bill: on that note, if you are reducing your calories and you think of bodybuilders in contest prep, their calories get so low that there, there is no room any longer for anything that’s processed.

I, I think that’s a safe, I I can say that confidently. Uh, yeah, sure. There’s an exception here or there, but when calories get too low and protein remains high, you’re eating that. That is a whole food diet at that point. And then one other strategy that I like, I don’t do it myself. Other people will, um, they’ll track macros.

They’ll elevate protein, but they’ll also have a fiber goal. And when you have like a, a fiber goal, let’s say like 38 gram, 40 grams for a male, or 25 for a female, now you’re, if you’re gonna hit that, that’s gonna force you to get more high fiber foods and beans or vegetable sources. So there’s another way to kind of use a macro tracking, flexible dining approach, but kind of bias it towards Whole foods.

Mike: I like that. I like that. And it, it, um, it also is, is easily defensible just because of the research that we have on the importance of, um, of eating enough fiber for maintaining health. It’s, it’s not a, it’s not essential in the way that, um, essential vitamins and minerals are. But if you wanna stay healthy, and if you want to reduce your risk of disease and dysfunction, you wanna make sure you’re eating enough fiber contrary to what, um, the carnivores would, would, uh, would have you 

Bill: believe

And, and then I, now I can see some people just buying Metamucil . Yeah. 

Mike: Yeah. That I, I, I’ve had people ask that, uh, as a, is that a hack? Can I, can I, uh, , can I hack the, uh, the, the advice by dropping the vegetables, eating the Pop Tarts, but ? And the answer is no. But just for anybody wondering, , what, what, what are your thoughts on those supplementing with fiber?

Let’s, let’s say somebody is eating a, a decent, uh, diet. Is there, is there value in adding a fiber supplement? 

Bill: I, I, I think my answer to that would be if they say, can I do that? I would say, you can to get your fiber, but it’s not the intention of why I would be putting fiber as a mac or as a goal in your eating plan.

The, and then, you know, I would talk about we, we have these, all of these unknown phytonutrients that are in the whole foods. That meta, I don’t wanna just brag on Metamucil whatever, whatever, fiber supplement. But that being said, if somebody’s just not gonna get fiber through food, then that’s probably, it’s probably a good choice.

It’s probably becomes a, a more health promoting choice to get that fiber. The, the more I learn about gut microbiota, the more I appreciate fiber intake. 

Mike: Yeah. Yeah, I think that, um, that, that makes a lot of sense to me. And, uh, if, if people are eating, let’s say they’re doing well, let’s say they’re getting a couple servings of fruit.

They’re getting four or five servings of vegetables, they’re getting in some leafy greens. Do you see any value in, uh, cuz in adding a fiber supple supplement? And the reason I’m asking this is people will ask me and they’ll hear that, oh, fiber’s good. And then they, they might jump to, well if, uh, if, if 20 to 40 grams, you know, depending on body size, if that’s good, is double that.

Bill: Great. Yeah. My, my gut reaction is I wouldn’t suggest a fiber supplement if you’re, if you’re getting your, your recommended 

Mike: intakes. Yeah, same. I mean, that’s, that’s why I don’t sell one, um, even though there’s, there’s a market for it. But I, I wouldn’t, I, I don’t know then how I would sell that, because what I’d be telling people is I actually would prefer if you just didn’t.

Buy this at all. I’d prefer if you just ate well. Yeah. 

Bill: That’s a But I guess strategy, right? . 

Mike: Yeah, exactly. But I guess if you’re not willing to eat, well, you could buy this, but then I’m, then I would feel like maybe I’m, I’m creating kind of a moral hazard. Like I’m enabling people. I’m encouraging them to not eat well.

Even if I’m telling them, Hey, um, I’d rather you eat well, but then it’s like actually just persuading them to buy it where they’re like, well, I mean, that’s nice that Mike cares for me, uh, like that, but hey, he sells this and he says that if I’m not gonna eat well, I can just take this even if it’s not as good

Anyway. So that, that’s, um, I think that’s a, I think that’s a good point. And back to this protein anchored, flexible dieting is, is there anything else you wanted to say on that? We have the calories. We have making sure we get enough protein. We have adding the fiber in if, if we want to understand even, I think that helps understand what an appropriate amount of nutritious.

Plant-based foods looks like, like if you start looking at how much fruit and vegetables and legumes and so forth that you need to eat to get to that, um, you can look at it in terms of servings. I’ve always just said, uh, you know, take a your, your fist. There you go. There’s a serving. And, you know, but, but looking at it, some people, they’re, they’re very, um, they like to work with exact numbers, and so that can also be a nice way.

Bill: Yeah. One thing I would add is that this protein anchored, flexible eating approach, it, it, it assumes that you’re living an active lifestyle. I, I don’t know if you’re, if you’re sedentary, do you, do you need protein to be that high? Probably not. Is it gonna hurt? No. But that, that’s, that’s building, you know, muscle for life.

It’s, it’s maintain that muscle. It’s helping you recover from your active lifestyle so that it’s, it’s, I look at it as the, that’s the, that’s the approach for an active person. 

Mike: Makes sense. And, um, as far as where that protein can come from, uh, this is again a question that I get asked that I might as well just toss to you while I have you, is people will wonder, okay, so if I’m supposed to eat, uh, call it somewhere around a gram per pound per day, if somebody is very overweight, it, it could be less obviously.

Um, but does that need to be all meat and does it need to be all animal products? How should I think about animal protein versus plant protein? 

Bill: Yeah, my answer to that is you, there should be an effort to get most of it from high quality protein sources, but you don’t have to. I, I count the protein in my, um, tortilla shell or I’ll count the protein in whatever that’s, um, that’s not from animal sources.

So you, your body just doesn’t need. All the central amino acids. So all protein counts, but there is, you should make an effort to get high quality sources. And for most people, that’s gonna be animal sources. And if it’s, if not going to eat animal sources, well then you are gonna just have to be a little more educated on getting protein from your vegetable sources that are complimentary so that they can become high quality.

Mike: And what does that look like? Because that, that’s usually what, it’s usually people who either are vegetarian or vegan or people like my wife, who she just doesn’t particularly like meat. Um, so she doesn’t eat much of it. 

Bill: Yeah. So, um, I think a, a common example that we always hear is rice is not a complete protein.

Beans are not a complete protein, but when you combine them, whatever rice was lacking, beans have extra of when the beans were lacking, rice has the extra of, so now when you have rice and beans, it is a complete protein source. So there’s, there’s one example, but now just on. In, in the, is that, is that 

Mike: correct though?

My understanding, and I might be wrong, but I remember looking at research some time ago, I believe it was m i t it was a study out of m i t that indicated that it’s, it’s not so much that, uh, the, the rice and the beans are missing essential amino acids. It, it, it, if you look at their amino acid profiles, it’s that, um, one, one could be strong in one regard.

Yes. And we get another 

Bill: not 

Mike: Yes. They’re not missing. Yes. We’re like, the leucine content in rice is not great and that matters for those of us who want to get more jacked. Uh, so if, if you combine the, the rice with, uh, a plant-based source that has more luine and then um, right in, let’s say, That, uh, rice, I don’t remember off the top of my head.

I don’t know, maybe it’s methyine or something could, could be high in one and low in the other. And you combine them and now you have something that when you look at it on an amino acid level, it looks kind of like whe for example. 

Bill: Yes. Yeah. I think a better way to phrase it, whatev, if rice is not optimal for one level, okay, the beans are more optimal for that.

Yes. Yeah. There are gonna have, they’re gonna have all of them. Um, and now there’s just, there’s plenty of, um, plant sources of protein that are commercially available as supplements that, that was not the case 20 years 

Mike: ago. So yeah, those are, yeah. I always recommend if, if people are gonna get most or all of their protein from vegetables or plant, plant foods, Rice is like, uh, rice and beans.

There’s a reason why that, uh, that that’s, that. I think that that’s a good recommendation. Um, tofu, Satan, um, a supplement helps a lot speci, uh, especially for women who don’t need to generally eat that much protein. Like if they can just supplement with, call it 30 grams a day, even that can help a lot toward reaching sufficiency.

And there are a lot of good clean plant supplements out there. I mean, I have one that has rice and pea protein and we chose, uh, those two because of their complimentary. amino acid profiles. And again, when you combine those, it actually looks a lot like way. So, yes. Awesome. Well, um, ed, this was a, a great discussion as usual and, um, very informative.

So thank you again for taking the time. And, and why don’t we, why don’t we just wrap up with where people can find you and find your work. Uh, I know you also, you have a, a guide on protein anchored, uh, flex Bleeding specifically, right? Yes. And it’s a couple of months away, but you might wanna mention your, your research review.

And we were talking what we were talking about actually before we got online. Yeah. If you wanna tell people what’s coming, so to, 

Bill: to find me. I’m on Instagram right now. I have a website that will be coming that’s, that’s not launched yet. So Bill Campbell PhD is my Instagram handle. And I’m, I kind of keep everybody informed of what I’m doing, my current research.

Bring, um, education about sports, nutrition, building muscle, losing fat there, and then in a few months, and, and I’m looking forward to coming back, uh, to where we can talk about, that’ll be our next one review. Um, I’ll be launching that early summer and it will be a research review that is solely focused on building muscle and losing body fat.

So all of the relevant research on those specific topics I’m going to review, um, I’m gonna bring experts in to help us apply that to your life. Or if you work with clients, how would, what are some strategies to apply that research into somebody’s actual life so that they can reap the benefits of implementing the, the 

Mike: research.

That’s great. And, uh, yeah, I’m looking forward to, to doing that. And also, um, I’ll just mention, and, and you, you’ll, you’ll make the, the decision whether you want to do this, but for people listening, uh, bill and I were talking about the idea that when he launches it, he, he might, it might make sense for him to just give that first issue away, uh, in exchange for an email address so then he can stay in touch with people who are interested in maybe subscribing to the, the subsequent issues.

And so, um, if, if that makes sense to Bill, then we will obviously mention that in this, um, in our next talk as well. And yes, tell everybody where they can get it. 

Bill: Yeah, no, that’s, that’s already been decided. That will be done, so yes. Cool. As soon as the, the website is launched and you can go to download it, I will, I will be all over that, but thank you.


Mike: Yeah. Yeah. Okay. Well hey, thanks again and I look forward to the next one. Me too. Well, I hope you liked this episode. I hope you found it helpful, and if you did subscribe to the show because it makes sure that you don’t miss new episodes. And it also helps me because it increases the rankings of the show a little bit, which of course then makes it a little bit more easily found by other people who may like it just as much as you.

And if you didn’t like something about this episode or about the show in general, or if you have, uh, ideas or suggestions or just feedback to share, shoot me an email, mike muscle for, muscle f o r, and let me know what I could do better or just, uh, what your thoughts are about maybe what you’d like to see me do in the future.

I read everything myself. I’m always looking for new ideas and constructive feedback. So thanks again for listening to this episode, and I hope to hear from you soon.

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