Here’s an ironclad canon of nutrition:

If you eat more calories than you burn, you’ll gain weight

And the more calories you eat, the more weight you’ll gain.

That begs the question, though . . . 

Is there a limit to how much fat you can gain in, say, a single day? 

Can 24 hours of uninhibited gluttony lead to several pounds of fat gain, as some claim? 

In other words, if you really “let yourself go,” how much fallout can you expect?

The long story short is you can gain a large amount of fat after a single day of bingeing, but it’s probably less than you think. 

By the end of this article, you’ll know how your body stores fat, how much fat you can really gain in a single day of overeating, and how to minimize fat gain if you have your heart set on engaging in some holiday hoggery.

 

How Much Fat Can You Gain in a Day?

Here’s the short answer: not as much as you might think.

For the longer (and more interesting!) answer, we can look to a study conducted by scientists at the University of Colorado. 

To simulate a bout of overeating, the researchers fed 16 men 50% more calories than they needed to maintain their weight every day (about 1,400 extra calories per day). 

After two weeks of gormandizing, they gained 3 pounds of fat. That works out to 1.5 pounds of fat per week or 0.2 pounds per day.

Now, this study wasn’t a perfect representation of a holiday binge. Most of us might overeat for a day or two but not several weeks, as in this study, but we can still use the data to ballpark how much fat we might gain when overeating for a day or two.

In this case, they gained ⅕ of a pound of fat when they maintained a 1,400 calorie surplus.

These results are bolstered by another longer study conducted by scientists at the Pennington Biomedical Research Center. 

In this study, the researchers had 29 slightly overweight men eat 40% more calories than they needed to maintain their weight every day for 8 weeks, which works out to a calorie surplus of 1,200-to-1,500 calories per day. At the end of the study, they’d gained 9 pounds of fat, or about 1.1 pounds per week or 0.16 pounds per day.

Despite snarfing high-calorie foods on the daily, once again they only gained about ⅕ of a pound of fat per day.

Finally, it’s worth looking at a study conducted by scientists at Loughborough University that looked at the effects of overeating high-fat foods for a single day.

The researchers had 15 healthy, normal weight, physically active (exercising at least 30 minutes three days per week) men and women eat 78% more calories than they needed to maintain their weight over the course of a single day. This worked out to 6,000 calories per day compared to their normal calorie intake of 3,350 calories per day.

Their diet was designed to be extremely high fat, providing 68% of total calories from fat. 

The researchers didn’t measure the participants body fat percentage, but they did record their weight before and after the all-day binge.

The result? 

On average, the participants gained 1.76 pounds. 

That’s considerably more than the other two studies, but much of the weight they gained wasn’t body fat. Plus, even if all of the weight these people gained was fat, two pounds of weight gain isn’t catastrophic considering how much these people ate. 

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Not All Weight Gain Is Fat Gain

Now, at this point you may be wondering why the results from these studies don’t line up with your experiences.

“Sure,” you might think, “studies show people don’t gain that much fat when they overeat, but why do I always gain 5-to-10 pounds after the holidays?”

The answer more or less boils down to four things: your sodium, carbohydrate, and water intake, and the weight of your stool.

You see, consuming large amounts of sodium, carbohydrate, and water causes a disproportionate increase in body weight despite not significantly increasing body fat.

And when most people eat a lot of food, they inevitably eat a lot more sodium and carbohydrate than normal. 

Now, sodium and carbohydrate don’t cause much weight gain on their own. Instead, they increase your body weight by increasing your whole-body water stores. 

Sodium brings water into cells, which is why eating large amounts of it can increase your total body water stores. Most people would call this “bloating” or “water retention” and you’ve probably noticed it after eating a large, salty “cheat meal,” like pizza, burritos, or fries.

A single high-sodium meal could increase your whole-body water stores enough to add several pounds to your body weight. This might increase your scale weight for several days before your body disposes of the excess sodium and water retention.

Carbohydrate Intake and Body Weight

Carbohydrate can have a similar effect on your body weight as sodium.

Carbohydrate is stored in the muscles and liver in the form of glycogen. Every gram of glycogen is stored with 3-to-4 grams of water, which means if you consume 400 grams of carbs, that could bring along 1200-to-1600 grams (~3 to 4 pounds) of water into your muscles and liver.

Taken together, the increase in sodium, carbohydrate, and water storage could bump your weight up by 5-to-10 pounds or more overnight. This can also give you a bloated, puffy appearance (which also goes away). 

The good news is your body will excrete most of this extra sodium and water, and your carbohydrate stores will gradually return to normal, but until this occurs you may think you’ve gained several pounds of fat if you go by your scale weight alone. 

Finally, another reason your body weight will skyrocket after a day or two of overeating is an increase in your stool weight. 

Until your body has digested and excreted all of the extra food mass from your feasting, you’ll likely be carrying around several additional pounds of food in your digestive tract, which further bumps up your body weight. This tends to go away after dropping the kids off at the pool a few times.

You see these effects in studies, too.

In the first study you learned about a moment ago, the participants gained 7 pounds of scale weight after 2 weeks of overeating, and in the second study, they gained 17 pounds after 8 weeks of overeating. In both cases, though, only about half of this increase in body weight was actual body fat (the rest being water, carbs, and stool).

The bottom line is if you eat 1,000 to 1,500 calories more than you need to maintain your weight in a single day, you’ll probably only gain ⅕ to ¼ of a pound of fat, even if your scale weight tells a different story.

Let’s say you really throw caution to the wind and eat 2,000-to-3,000 calories more than you need to maintain your weight (fairly common on Thanksgiving). The damage? 

Maybe half a pound of fat gain.

Now, the one big caveat here is that this assumes you’re only overeating for a day or two. It’s continuous overeating that leads to weight gain, obesity, diabetes, and the many other health complications associated with overeating.

What If You Eat A Lot More than Normal?

Most of the studies we’ve looked at so far involved people “bingeing” on 1,000-to-1,500 more calories than they needed per day.

But what if you’re the kind of person who likes to really “turn it loose” when you go off the rails?

You know, instead of eating a large bowl of oatmeal and a bar of chocolate (~1,000 calories), you decide to demolish an entire pizza, a milkshake, and a 16-ounce pack of Twizzlers (6,000 calories).

What’ll the consequences be?

It’s impossible to say exactly how much you’ll gain for reasons you’ll learn in a moment, but let’s try to puzzle this out with napkin math.

Let’s say you need 3,000 calories to maintain your weight every day.

On the day of your binge, you eat 2,000 calories from your normal meals, and 6,000 calories from your pizza, milkshake, and Twizzlers.

2,000 + 6,000 = 8,000 total calories eaten.

8,000 calories eaten – 3,000 calories burned = a 5,000 calorie surplus.

In the studies you learned about earlier in this article, people gained around 0.2 pounds of fat per 1,000 calories they ate above their maintenance needs. 

If you ate five times that amount—5,000 calories more than you need to maintain your weight—you could expect to gain about a pound of fat.

You can get rid of that with about a week of proper dieting.

(And if you’d like specific advice about how many calories, how much of each macronutrient, and which foods you should eat to lose fat quickly, take the Legion Diet Quiz.)

If we look at real world examples of extreme hedonism, like Thanksgiving, Christmas, and New Years, then we have even less reason to worry. On average, people only gain around one pound of body weight during the holidays. 

Talk with people who’ve partaken in binges like this, and you’ll quickly realize they often don’t gain as much fat as you’d expect. After a few days of eating normally and allowing their extra water, sodium, and glycogen stores to decrease, their weight settles back to where it was before the calorie bonanza.

In other words, calorie intake and fat gain don’t go up in lockstep. 

5 Ways to Enjoy the Holidays without Gaining Lots of Fat

Every holiday season you’ll find a number of articles on how to “avoid holiday weight gain.” 

Most of the time, these articles are stuffed with useless platitudes like “watch your portion sizes,” “skip dessert,” and “use a smaller plate.” 

Yeah . . . no. 

Not only are these strategies largely ineffective (what good is a smaller plate if you get seconds and thirds?), most people will never follow them. That goes for me, too.

I don’t know about you, but I look forward to enjoying generous portions of many different dishes during the holidays. While I don’t engorge to the point where I’m forced to lie on the couch like a harpooned Beluga, I’m also not going to let concerns about gaining a small amount of fat spoil my fun.

Remember—it’s continuous overeating that leads to weight gain, a flabby physique, and poor health, not the occasional high-calorie indulgence. 

That doesn’t mean you have a license to go hog wild, either. Although you may not gain as much body fat as you’d expect when overeating, that isn’t an excuse to turn Thanksgiving to New Year’s into one long binge.

With that in mind, here are some strategies for enjoying the holidays without gaining too much fat (that actually work).

1. Eat a few large meals, then stop.

One of the primary reasons people gain so much fat during the holidays is they never stop eating. 

Instead of having a large Thanksgiving dinner and maybe a few high-calorie leftover meals, they eat several large meals and put down on cookies, candy, and dessert in the interim. 

This is particularly true of people who’ve been in a calorie deficit for quite some time before the holidays, who’ve spent the past few weeks salivating in anticipation of the coming feast.

Don’t do that.

Instead, eat a few large, high-calorie meals, and maybe a few snacks here and there, but know when you’ve had enough.

In other words, have a few large meals with all of the foods you want, but don’t continue grazing on cookies, pie, and so forth long after you’re stuffed. 

2. Eat lots of protein and some fruits and vegetables.

You’ve probably experienced the feeling of eating 5 (or 10 or 15) cookies, and still not being full. 

Why? 

Most of the calories in foods like cookies come from refined carbs, sugar, and fat, which aren’t very filling (despite being high in calories).

Protein, however, is more satiating than carbs or fat. Likewise, foods high in fiber such as fruits and vegetables also promote fullness better than foods high in refined carbs, sugar, and fat. 

Now, I’m not saying you need to abstain from all processed foods and stick to turkey and Brussels sprouts, but including some high-protein and high-fiber foods is an easy way to help limit wanton piggishness. 

In short, fill up on protein, veggies, and fruits first, then turn your attention to the really calorie dense foods like cookies, cakes, and so on.

3. Stay active and stick to your normal workout routine as best you can.

The struggle to avoid fat gain during the holidays is more mental than physical. 

That is, squeezing in a few workouts over the holidays isn’t going to burn enough calories to offset how much you eat. 

What it will do, though, is remind you that fitness is a priority. Each workout forces you to think about why staying in shape is important to you and how much more enjoyable it is to inhabit a fit, firm, healthy body than an out-of-shape, flabby, unhealthy one. In other words, it’s a moment of episodic future thinking.

You see, I have a little theory that one of the main reasons people fall “off the wagon” after overeating, such as during the holidays, is they let their entire health and fitness routine fall by the wayside. 

They don’t just overeat—they also stop working out, stop weighing themselves, stop eating any fruits or vegetables, and they stay up late, drink too much, and so forth. 

In other words, people shoot themselves in the foot by telling themselves they’ve “blown their diet,” and then use this as an excuse to abandon all of their healthy habits throughout the holidays. 

Of course, in the back of their minds they know the chickens will come home to roost soon, but that’s a problem for future Homer, not present Homer.

Aside from the other solutions on this list, one way to avoid this problem is to stick to your normal fitness routine, despite overeating. 

That is, even though you’re eating a lot more than you normally would, keep working out, staying active, eating lots of fruits, vegetables, and lean protein, and getting to bed on time. 

If you’re really feeling brave, keep weighing yourself. The number will be higher, of course, but it’s staying in the habit of monitoring your weight that counts. 

Maintaining a few keystone habits like working out also makes it easier to jump back into your normal routine when the holidays are over.

4. Reduce your calorie intake before and after your big meals.

Some people practice intermittent fasting throughout the holidays so they can save their calories for big meals. 

While this strategy can work, I prefer to maintain my normal meal frequency, but eat smaller meals when I’m not feasting.

I also keep these meals low in calories and high in protein. For example, the morning of Thanksgiving I’ll typically have some fruit and a lean source of protein, like some sliced apples and strawberries with Greek yogurt or whey protein powder. 

That evening, assuming I want to eat anything at all after the Thanksgiving meal, I’ll probably have something similar, such as some low-fat cottage cheese or some leftover turkey before bed. 

5. Cut after the holidays, not during.

After a day or two of overeating, many people feel the need to start cutting immediately to get rid of any fat they may have gained. 

While it’s fine to stay in a calorie deficit if you simply don’t feel like eating much (which is usually the case for me), I’d caution against crash dieting.

Instead, I recommend you maintain a slight calorie deficit for a week or two after the holidays to shave off any fat you gained. If you kept fat gain in check with the other tips on this list, that should be sufficient to get back to your pre-holiday body.

+ Scientific References