What 33 Studies Say About the CICO Diet for Weight Loss

“Out of intense complexities, intense simplicities emerge.”

— Winston Churchill

Weight loss can seem wildly complex.

Some say that carbs are the culprit when it comes to weight gain, and going low-carb is the most effective way to lose weight and keep it off for good.

Others say that weight loss goes beyond carbs—it’s about the quality of your diet.

If you avoid toxins, lectins, phytates, and other nutritional bogeymen that are menacing your metabolism, the pounds fall right off.

And others say that you just need to eat clean. Eat more fresh, whole, minimally processed foods and less junk, and you’ll lose weight like clockwork.  

Most trends ebb and flow in cycles—liberals and conservatives in power, booms and busts in the economy, and complexity and simplicity when it comes to popular diets.

It’s not surprising then, that after several decades of fake doctors, fitness gurus, and marketers shilling complex diets like The Plant Paradox diet, the ketogenic diet, the carnivore diet, the military diet, and the like, that many people are yearning for a simpler approach.

It’s not surprising, then, that people are becoming tired of complicated diets, and are becoming more interested in simple ones, like the “calories in, calories out” diet, aka the CICO diet.

Proponents promise that it’s the simplest, most reliable, and effective way to lose weight, and that once you try it you’ll never try another weight loss diet again.

Critics say that while it can help you lose weight, it does so at the cost of your long-term health.

Who’s right?

The short answer is that the CICO diet isn’t really a diet at all. It simply describes the mechanism by which all diets work and have always worked—eating fewer calories than you burn.

As the old saying goes, though, everything old is new again, and in this article, you’re going to learn why the CICO diet is being exhumed once more.

By the end, you’ll know . . .

• What the CICO diet is
• Why people follow the CICO diet
• What the benefits and downsides of the CICO diet are
• A better way to eat than the CICO diet
• And more!

Let’s get started.

(Or if you’d prefer to skip all of the scientific mumbo jumbo, and you just want to know how many calories, how much of each macronutrient, and which foods you should eat to reach your health and fitness goals, no problem! Just take the Legion Diet Quiz, and in less than a minute, you’ll know exactly what diet is right for you. Click here to check it out.)

Table of Contents

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• What Is the CICO Diet?
• What Are the Benefits of the CICO Diet?
• What Are the Downsides of the CICO Diet?
• A Better Way to Eat
• The Bottom Line on the CICO Diet

Want to listen to more stuff like this? Check out my podcast!

What Is the CICO Diet?

In a nutshell, the CICO diet involves three steps:

1. Estimating how many calories you burn per day.
2. Tracking how many calories you eat per day.
3. Measuring food portions to ensure that you eat fewer calories than you burn every day.

CICO stands for “calories in, calories out,” an aphorism that describes the principle of energy balance.

Energy balance is the relationship between the amount of energy that you feed your body and the energy it burns.

This energy is expressed in kilocalories, also referred to as just “calories,” and one calorie is the amount of energy it takes to heat one kilogram of water one degree Celsius.

As you probably know, various foods contain varying amounts of calories (energy). For example, nuts are very energy dense, containing about 6.5 calories per gram, on average. Celery, on the other hand, contains very little stored energy, with just 0.15 calories per gram.

Now, if you add up the calories of all the foods that you eat every day, you’ll have your total caloric intake.

If you add up how much energy you’re burning every day through basic physiological processes and all physical activity, you’ll have your total daily energy expenditure (TDEE).

Compare these two numbers and you’ll notice one of three things:

1. You’re consuming more energy than you’re burning.

This puts your body is in a state of “positive energy balance,” and the result is weight gain over time. (You’ll learn more about why soon.)

2. You’re burning more energy than you’re consuming.

This puts your body is in a state of “negative energy balance,” and the result is weight loss over time.

3. You’re burning more or less the same amount of energy as you’re consuming.

This puts your body is in a state of “neutral energy balance, and the result is weight maintenance.

The CICO diet focuses on the second of these three states: maintaining a negative energy balance.

This doesn’t necessarily mean you have to be in a negative energy balance every day, but your calorie intake over time needs to be lower than your expenditure to lose weight.

So, at the bottom, the CICO diet is just calorie counting.

You don’t have to eat a particular list of foods or avoid others.

You don’t have to take any supplements.

You don’t have to exercise.

All you have to do is figure out how many calories you burn every day, track how many calories you eat, and make sure you eat fewer calories than you burn.

How well does this approach work, though?

Let’s find out.

What Are the Benefits of the CICO Diet?

Most people follow the CICO diet after trying (and failing) to lose weight following other diet strategies.

Thus, it’s not surprising that the main reason people follow it is that it works.

The second main reason people follow it is also simple and influenced by their experiences following other diets: you can eat whatever you want and lose weight.

Let’s look at both of these factors in more detail.

It Works Every Time, Everywhere

The single most important benefit of the CICO diet is that it works.

It doesn’t matter how much you weigh, how long you’ve been overweight, how many diets you’ve tried in the past, or what foods you do or don’t eat.

If you follow the diet correctly—ensuring you’re in a calorie deficit more often than not, you’ll lose weight.

Now, if you think I’m drinking decades old Kool-Aid, this is probably you right now:

Before your becomeoutraged.exe script runs and you bounce off this page, though, hear me out.  

No matter what fitness gurus, fake doctors, and diet book authors claim, every successful weight loss diet works because it forces you to be in a calorie deficit.

Typically, though, these diets use indirect means to reduce your calorie intake such as . . .

• Limiting the variety of foods you can eat (paleo, keto, low-carb, carnivore, Mediterranean)
• Limiting when or how often you can eat throughout the day (intermittent fasting)
• Limiting portion sizes of certain foods (Weight Watchers)

. . . all of which naturally reduce your calorie intake.

When most people begin one of these approaches, their calorie intake drops far enough below their calorie expenditure that they rapidly begin to lose weight.

This strategy can work, but it’s also easy to mess up.

As you become more accustomed to your new diet, it becomes easier and easier to overeat while still following the rules of the diet.

For example, many people who begin following a ketogenic diet lose weight quickly at first, but when they get used to eating fatty meat at every meal, making high-fat substitutes for their favorite foods using high-calorie ingredients like almond flour, coconut oil, and butter, it becomes much easier to consume more calories than you expend.

Eventually, your average calorie intake rises, the calorie deficit created by your diet disappears, and you’re left scratching your head as to why you stopped losing weight.

The CICO diet short circuits this process by attacking the root cause of weight gain: excess calories.

Instead of focusing on arbitrary rules that indirectly reduce your calorie intake, the CICO diet throws all of the rules out the window save for one: you must eat fewer calories than you burn.

In other words, it’s simply a method of dieting that abides by the first law of thermodynamics.

This is why every single controlled weight loss study conducted in the last 100 years, including countless meta-analyses and systematic reviews, has concluded that meaningful weight loss requires energy expenditure to exceed energy intake.

That’s also why bodybuilders dating back just as far, from Sandow to Schwarzenegger and all the way up the line, have been using this knowledge to systematically and routinely reduce and increase body fat levels.

And that’s why new brands of “calorie denying” come and go every year, failing to gain acceptance in the weight loss literature.

The reality is a century of metabolic research has proven, beyond the shadow of a doubt, that energy balance is the basic mechanism that regulates weight gain and loss.

All that doesn’t mean you have to count calories to lose weight, but it does mean you have to understand how calorie intake and expenditure influence your body weight and eat accordingly.

Not convinced by scientific research?

Perhaps the story of Professor Mark Haub can win you over. He lost 27 pounds in 10 weeks eating 1,800 calories worth of Hostess cupcakes, Doritos, Oreos, and whey protein shakes per day.

Or the story of science teacher John Cisna, who lost 56 pounds in six months eating nothing but 2,000 calories worth of McDonald’s per day.

Or the story of Kai Sedgwick, who got into the best shape of his life following a rigorous workout routine and eating 2,700 calories worth of McDonald’s every day for a month.

Now, I don’t recommend you follow in their footsteps (for reasons we’ll go over in a moment), but it proves a point:

When it comes to weight loss or gain, energy balance is king.

And that’s why the CICO diet works every time, for every person, under all circumstances.

Summary: The main reason the CICO diet is becoming more and more popular is because it always works, no matter how overweight you are, how many times you’ve failed before, or what you eat.

You Can Eat Whatever You Want and Lose Weight

When it comes to weight loss, how much you eat is more important than what.

Yes, eating plenty of nutritious foods is important for overall health, longevity, and vitality, but there are no foods that cause weight loss or weight gain.

Carbs don’t cause fat gain.

Fat doesn’t burn fat.

Gluten doesn’t halt weight loss or cause fat gain.

I could keep going, but the fact is that no food or food group is going to significantly help or hinder your ability to lose weight in and of itself.

Hopefully, this is starting to make sense in light of what you learned about energy balance.

Now, of course, some foods are easier to overeat than others because they’re higher in calories and less satiating than other foods, but they can’t cause fat gain unless they contribute to a calorie surplus.

While some people use this newfound freedom as a license to gorge on as much junk food as possible while losing weight, most people wield this knowledge for good.

Instead of obsessing about eating the right “fat burning foods” and avoiding “fattening foods,” the CICO diet allows you to loosen up and enjoy the occasional, guilt-free treat while continuing to lose weight.

As long as you eat fewer calories than you burn, you can enjoy desserts, restaurants, or simply a high-calorie home-cooked meal that would normally be verboten on traditional weight loss diets.

This flexibility makes dieting significantly more enjoyable and sustainable, which in turn is what drives long-term weight loss and weight maintenance.

Summary: The CICO diet gives you unlimited flexibility in what you do or don’t eat, which makes losing weight significantly more enjoyable and sustainable.

What Are the Downsides of the CICO Diet?

The main problem with the CICO diet isn’t a problem with the diet itself, but with how it’s perceived by people interested in trying it.

People have a tendency to take things very literally, and especially when it comes to diet and fitness advice, often abandoning common sense in the process.

With a name like the “calories in, calories out diet,” some people wrongly assume that people who follow this diet only focus on calorie intake. While regulating calorie intake is technically the only hard and fast rule of the diet, this isn’t how most people use the diet in practice.

This is why it’s better to think of these “drawbacks” of the CICO diet as “potential pitfalls” that you can easily avoid with the right preventative measures.

Let’s go over each.

It Can Increase the Risk of Nutrient Deficiencies

Look at any popular article on the CICO diet and it will likely make this point:

The CICO diet is unhealthy because it disregards diet quality, eschews whole foods, and allows boatloads of junk, which raises the risk of nutrient deficiencies, poor health, and decreased longevity.

This is a valid concern.

When many people learn they can eat whatever they want and lose weight—particularly if they’ve been following a highly restrictive diet for quite some time—they swing to the other extreme.

They eat like a 12-year old whose parents are permanently on vacation, with the only difference being they’re staying in a calorie deficit.

If you don’t believe me, witness the #IIFYM hashtag on Instagram, or this guy, who lost 32 pounds eating nothing but ice cream, children’s cereal, alcohol, and protein shakes for 100 days.

While it’s possible to get and stay lean on a diet like this, body composition isn’t a perfect barometer for health.

Just as it’s possible to be slightly overweight and healthy, it’s also possible to be at a normal weight but be unhealthy due to poor diet and exercise choices.

If you forsake fruits, vegetables, whole grains, and high-quality protein for Oreos, Doritos, pizza, and Pop Tarts, then it’s extremely difficult to get all of the vitamins, minerals, and other nutrients your body needs to function at its best.

This is even more true when restricting your calories to lose weight, as it becomes even harder to get all of the nutrients your body needs from food.

The good news is that this problem is easily avoidable if you follow a few simple eating guidelines:

1. Get at least 80% of your calories from whole, minimally processed, nutrient-dense foods.
2. Eat at least three to five servings of fresh fruits and vegetables per day.

If you stick to those guidelines, then you’ll likely meet or exceed most of your daily requirements for vitamins, minerals, and other nutrients.

In fact, I’d argue that following the CICO diet ends up being more nutritious for most people than following a typical weight loss diet based on excluding a particular food or food group.

These kinds of diets often put people at a higher risk of developing nutrient deficiencies than people who eat a wider variety of foods, even if they also eat some less healthy treats in moderation.

From what I’ve seen, it’s typically the #hardcore fitness crowd who uses this diet a license to deprive their bodies of essential nutrients. Normal people simply use it as a way to make losing weight a more enjoyable, healthy, and sustainable.

Summary: To avoid nutrient deficiencies, it’s best to make sure you get at least 80% of your daily calories from whole, minimally processed, nutritious foods, even if you don’t need to in order to lose weight.

You May Not Eat Enough Protein

The single biggest legitimate failing of the CICO diet is that it doesn’t offer any guidance as to how you should divide your calories into protein, carbs, and fats.

This is particularly true when it comes to protein intake.

Study after study has confirmed that high-protein dieting is superior to low-protein dieting in just about every meaningful way, and especially in the context of weight loss.

Specifically, research shows people who eat more protein:

• Lose fat faster
• Gain more muscle
• Burn more calories
• Experience less hunger
• Have stronger bones
• Generally enjoy better moods

And protein intake is even more important when you exercise regularly because this increases your body’s demand for amino acids (which are provided by protein).

Eating adequate protein is also vital for preserving lean mass while dieting, which is just as important as the fat you’re losing. If you lose too much muscle while losing weight, you’ll wind up skinny fat.

Protein intake is important among sedentary folk as well. Studies show that such people lose muscle faster as they age if they don’t eat enough protein, and the faster they lose muscle, the more likely they are to die from all causes.

In terms of how much protein you should eat, research conducted by scientists at Auckland University of Technology found you should aim for 0.8 to 1.2 grams of protein per pound of body weight per day to lose as much fat and as little muscle as possible while cutting.

This is about twice as much as the RDA for protein and significantly more than most people get in their normal diets.

Most adults consume around 0.5 grams of protein per pound of body weight per day in the United States, which works out to around 90 grams of protein per day.

If most of these people were to follow the CICO diet as it’s typically practiced—reducing their calorie intake without paying attention to their protein intake, they’d almost certainly end up eating even less than this amount.

This is why many people who only count calories to lose weight end up being disappointed with how they look in the end. They lose weight, much of which is fat and some of which is muscle, which results in the skinny fat look most people wish to avoid.

The best way to prevent this from happening is to ensure you eat enough protein every day while following the CICO diet. You’ll learn how to do this in a moment.

Summary: If you follow the CICO diet, you also need to ensure that you eat adequate protein, or a significant portion of the weight you lose will be muscle instead of fat.

A Better Way to Eat

The CICO diet isn’t really a “diet” in the traditional sense.

Instead, it’s a method that can be applied to any eating strategy you choose.

I like the way Eric Helms, a natural bodybuilder, powerlifter, and member of Legion’s Scientific Advisory Board explains it.

He describes energy balance, which is just another term for CICO, as the base of the pyramid upon which a successful weight loss diet is built.

Here’s a graphic that shows this nicely:

If you master energy balance, aka CICO, then you’ll be able to lose weight no matter how the rest of the pyramid looks.

If you want to lose fat instead of muscle, improve your long-term health, and enjoy your diet as much as possible, then you also want to optimize the other levels of the pyramid, too.

While it isn’t listed on this pyramid (which only applies to diet), the kind of exercise you do is also a deciding factor in determining how your body looks and feels after following a calorie-restricted diet.

So, I’m also going to include some basic exercise guidelines for fat loss while following the CICO diet.

Here’s how to use CICO to lose fat and not muscle:

Step 1: Maintain an aggressive but not reckless calorie deficit of about 25% when cutting.

In other words, when you’re cutting I recommend that you eat about 75% of your TDEE.

I didn’t pick this 25% number out of thin air, either. Research shows it works tremendously well for both fat loss and muscle preservation when combined with resistance training and high protein intake.

You can calculate this number by first estimating your TDEE using this calculator . . .

Unit

Imperial Metric

Gender

Male Female

Weight

Height

3'0" 3'1" 3'2" 3'3" 3'4" 3'5" 3'6" 3'7" 3'8" 3'9" 3'10" 3'11" 4'0" 4'1" 4'2" 4'3" 4'4" 4'5" 4'6" 4'7" 4'8" 4'9" 4'10" 4'11" 5'0" 5'1" 5'2" 5'3" 5'4" 5'5" 5'6" 5'7" 5'8" 5'9" 5'10" 5'11" 6'0" 6'1" 6'2" 6'3" 6'4" 6'5" 6'6" 6'7" 6'8" 6'9" 6'10" 6'11" 7'0" 7'1" 7'2" 7'3" 7'4" 7'5" 7'6" 7'7" 7'8" 7'9" 7'10" 7'11" 8'0" 8'1" 8'2" 8'3" 8'4" 8'5" 8'6" 8'7" 8'8" 8'9" 8'10" 8'11" 9'0"

Age

Activity

None (little to no physical activity) A little (1 to 3 hours of exercise or sports per week) Some (4 to 6 hours of exercise or sports per week) A lot (7 to 9 hours of exercise or sports per week) A TON (10+ hours of exercise or sports per week) Custom activity multiplier

1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95

BMR formula

The Mifflin-St Jeor formula is generally the most accurate if you don't know your body fat percentage.

Katch-McArdle Mifflin-St Jeor (Recommended) Revised Harris-Benedict

Body Fat %

Not sure what your body fat percentage is? Use the Legion Body Fat Percentage Calculator to find out!

Your Stats

2,679

Total Daily Energy Expenditure (TDEE)

1,786

Basal Metabolic Rate (BMR)

No activity 2,053

A little activity 2,321

Some activity 2,679

A lot of activity 3,036

A TON of activity 3,393

Calories to lose weight

Slow (0.5 lb per week) 2,545

Moderate (1 lb per week) 2,464

Fast (2 lb per week) 2,384

Calories to gain weight

Slow (0.5 lb per week) 2,812

Moderate (1 lb per week) 2,893

Fast (2 lb per week) 2,973

. . . then multiplying the answer by 0.75, or you can use the back-of-the-envelope method of . . .

10 to 12 calories per pound of body weight per day.

This simple formula will give you a nearly identical number without the hassle of using a TDEE calculator for weight loss.

If you get nothing else out of this article, make it this: If you want to lose weight using CICO, eat 10 to 12 calories per pound of body weight per day.

Do that, and you’ll see results.

Read this article to learn about the science behind these recommendations and how to customize them to your needs:

How Many Calories You Should Eat (with a Calculator)

Step 2: Eat 0.8 to 1.2 grams of protein per pound of body weight.

This is enough to minimize muscle loss and maximize satiety and the thermic effect of food.

If you’re a very overweight (a man with 25%+ body fat or a woman with 30%+), I recommend you set your protein intake at 40% of your total calories.

Read this article to learn about the science behind these recommendations:

How Much Protein Do I Need? The Definitive (and Science-Based) Answer

Step 3: Do lots of heavy, compound weightlifting.

If you don’t get the first two steps right, what you do in the gym won’t matter very much.

Proper dieting is just that important.

If you do, though, the right workout program will make a huge difference in how quickly you can lose fat without losing (or while gaining) muscle.

And the best types of workout programs for natural weightlifters are those that focus on heavy compound exercises like the squat, deadlift, bench press, and military press.

Sure, you can gain muscle and strength in many different ways, but decades of scientific and anecdotal evidence have conclusively proven that this is the most effective approach.

The reason heavy compound weightlifting is so powerful is simple: it’s the best way to progressively overload your muscles.

And by “progressively overloading” your muscles, I mean increasing tension levels in them over time. This is the primary driver of muscle growth, and while there are several ways to do this, the most effective one is just getting stronger.

Not only is this the most effective way to build muscle when you’re bulking, it’s also the best way to preserve muscle when you’re cutting.

If you want to learn more about how to set up a workout program for losing fat, check out this article:

The Definitive Guide on How to Build a Workout Routine

Step 4: Take supplements that are proven to increase fat loss.

Here’s a dirty little secret of the supplement industry:

99% of what you see, hear, and read about fat loss supplements is pure blarney.

You can read this article to learn why, but some of the worst offenders include Garcinia cambogia, green coffee bean extract, and raspberry ketones. And others, like Hoodia, have even turned out to be toxic.

So if you’re skeptical of fat loss supplements, I understand.

That said, there are safe, natural compounds that do effectively speed up fat loss. When you combine the right supplements with a proper diet and exercise routine like you just learned about, you dramatically speed up the process.

Here are the top three fat loss supplements that actually work:

1. Caffeine. Three to six mg per kilograms of body weight per day is enough to maximize the fat-burning effects of caffeine. As weight loss boils down to energy consumed versus energy expended, caffeine helps you lose fat by increasing your body’s daily energy expenditure.

Caffeine also improves strength, muscle endurance, and anaerobic performance, and also reverses the “morning weakness” experienced by many weightlifters.

You can get caffeine from coffee or any other source, but I prefer to get mine from Pulse, which also contains six other ingredients proven to boost workout performance and improve mood and energy levels.

2. Yohimbine. 0.1 to 0.2 mg per kilogram of body weight taken before fasted training can increase fat burning during your workout, particularly of stubborn fat stores.

You can buy pure yohimbine supplements, but I recommend you try my pre-workout fat-burner supplement, Forge. Along with 10 mg of yohimbine per serving, it also contains HMB free acid and citicoline, which help prevent muscle breakdown and boost mood during workouts.

3. Phoenix. One to two servings per day is enough to maximize the fat-burning effects of Phoenix, a fat burner that Legion developed that contains seven natural compounds proven to help you lose fat faster, including synephrine, green tea extract, and forskolin.

The Bottom Line on the CICO Diet

The CICO diet involves estimating how many calories you burn, tracking how many calories you eat, and eating fewer calories than you burn in order to lose weight.

That’s it—there are no other rules to follow.

The benefits of the CICO diet are that it reliably works for everyone, under all circumstances, all the time, because it abides by the first law of thermodynamics.

It also offers endless flexibility, as you’re allowed to eat any food or food group you wish, so long as it fits your calorie targets.

The only two potential pitfalls of the CICO diet are that it can increase the risk of nutrient deficiencies and may not provide enough protein to optimize body composition while cutting.

Luckily, both of these problems are easily avoided by getting at least 80% of your calories from whole, minimally processed, nutrient-dense foods and eating at least three to five servings of fruits and vegetables per day.

While following the CICO diet will help you lose weight, you need to follow a few more steps to ensure most of the weight you lose is fat, not muscle. They are . . .

1. Maintain an aggressive but not reckless calorie deficit of about 25% when cutting.
2. Eat 0.8 to 1.2 grams of protein per pound of body weight.
3. Do lots of heavy, compound weightlifting.
4. Take supplements that are proven to increase fat loss.

Follow this “upgraded” CICO diet, and you’ll get the body you want.

Oh, and if you aren’t sure if the CICO diet is right for your circumstances and goals, then take the Legion Diet Quiz! In less than a minute, you’ll know exactly what diet is right for you. Click here to check it out.

What’s your take on CICO diet? Have anything else to share? Let me know in the comments below!