How Much Fat Can You Gain In A Day Of Overeating?
Eat more calories than you burn and you’ll gain weight. This is a universal truth of energy balance. But how much? Specifically, how much fat can you gain in a day of overeating?
You’re not a robot. And you’ll never be perfect with your diet, despite the high expectations you set for yourself.
But a day of overeating can leave you hating yourself and feeling like you fucked up.
The morning after the night before consists of a nervous trip to the bathroom to assess the “damage”.
But there’s no need to feel that way. In fact, the amount of fat you can gain in a day isn’t that much. So your dietary digression is unlikely to be the fat loss train wreck you’ve made it out to be.
In this article, you’ll you’ll learn the science behind overeating and how much body fat you can expect to gain after one day of pizza, wine, and ice cream.
So, if you want to finally put your mind at rest and stop beating yourself up when you overeat, read on.
And if you’d prefer to listen to the audio version of “How Much Fat Can You Gain In A Day?”, click the play button below.
How Much Fat Can You Gain In A Day?
You and I have both been in the situation where we ate more than planned. Despite your best intensions, you went over your calorie target. And now you feel deflated (or bloated, depending on how you look at it).
First things first, it’s important to know that you may not put on ANY body fat when you exceed your calorie target.
For example, if calorie maintenance is 2,000 kcals per day, conceivably your deficit might be c.500 kcals per day, leaving you with a daily target of 1,500 kcals. Then, let’s assume you ate exactly 500 kcals over your target. Bummer!
But you didn’t exceed calorie maintenance. Therefore, you didn’t gain any body fat that day. Sometimes you simply need to keep things in perspective and look at the bigger picture.
However, let’s assume you DID overeat and exceeded your maintenance calories. How much body fat did you gain?
Thankfully, it’s not as much as your brain is telling you. And we can look to the research to help illustrate the point. In an 2 week study, 16 participants were overfed by c.1,400 kcals per day. At the end of the study the average amount of body fat gain was 3 lbs (about 1.4kg), or 0.2 lbs (about 0.1kg) per day.
Another study looked at a longer period of overfeeding, this time 8 weeks. In this study, subjects ate 40% above maintenance calories. By the end of the 2 months, the average body fat increase was approximately 9 lbs (c.4kg), or 0.16 lbs (c. 0.07kg) per day.
These studies highlight that overeating 1,200 – 1,500 calories per day doesn’t lead to huge increase in stored body fat.
Why Do You See Much Bigger Increases On The Scale?
So if the amount of fat you gain after one day isn’t that much, why do you see such a huge jump on the scales?
The answer relates to sodium, carbohydrate, and water. In reality, a spike in your scale weight overnight is unlikely to have much to do with body fat.
I’m sure you’ve been in the situation where you’ve over-indulged one evening, right?
Typically, when you overeat, you’ll tend to have more sodium and carbohydrates than an average day. In turn, this leads to water retention and the replenishment of glycogen (stored glucose).
Glycogen is stored in the muscles, liver, and blood to varying degrees and are depleted during a calorie deficit. And for each gram of glycogen stored, you’ll also store c.3g of water. This isn’t a bad thing. It’s perfectly normal and NOTHING to worry about.
When you’re in an energy deficit, ie dieting, your body utilises these glycogen stores to fuel the deficit you’ve created.
A bout of overeating may cause your glycogen stores to be partially, or fully replenished, potentially leading to several kilos of weight gain.
But this is NOT body fat. So don’t shit yourself when you jump on the scales, the night after demolishing your Dominos.
What About When You Eat A LOT? Can You Gain More Fat In A Day?
What about if you really push the boat out and go balls deep in pizza, donuts, ice cream, and anything you can lay your hands on? How much fat can you gain in a day eating like that?
In truth, it’s impossible to be exact. But there’s a rough rule of thumb you can use.
It takes c.7,700 calories to burn or gain 1kg of body fat.
Let’s assume your calorie maintenance is 2,000 kcals/day and your day of overeating resulted in you exceeding that number by 3,000 kcals. A total of 5,000 kcals for the day.
At most, the 3,000 kcal surplus would result in c. 0.4kg of body fat gain. Although, this assumes none of those excess calories went to building muscle or any other processes and functions in the body.
And 0.4kg in the grand scheme of things is not really worth worrying about, right? After 1-2 weeks of a calorie deficit, it’ll be like it never happened.
So even if the scales jump by 2-3kg overnight, your body fat gain in that single day was probably less than half a kilo.
Obviously, if you were to continue eating in that manner, your weight would exponentially increase over time, which isn’t what you want (I’m assuming).
The Science Behind Why You Don’t Gain As Much Fat As You Think
You might still be a little confused as to why these larger overfeeding scenarios don’t cause a greater single-day increase in body fat.
Essentially, it comes down to 4 things:
- Thermic Effect Of Food (TEF). Your body uses more energy to burn certain macronutrients.
- Macro Composition. Your body stores body fat more easily depending on what foods you ate.
- Increased activity. With an increase in calories, you might move more, resulting in more calories burned that day.
- Nutrient Absorption. You don’t absorb all of the calories from the food you eat, ie fibre.
Thermic Effect Of Food (TEF)
The digestion and absorption of food requires energy. Consequently, each time you eat, your body uses calories in order to make use of the nutrients you consumed. And the thermic effect of macronutrients, differs.
Protein is the most energy expensive nutrient to digest, with 20-35% of the calories being used during digestion and absorption. This is one reason why a higher protein diet can be more effective for fat loss. So if you were to consume 100 k/cals of Protein you would use up 20-35 k/cals digesting, absorbing and disposing of it.
In comparison, approximately 5-15% of the calories of carbohydrates and fats are used within the digestion process.
For more information on TEF and the basics of calories and macros, click here to download the Iron Paradise Fitness Guide To Calories. It’s a FREE resource providing you with everything you need to know about calories, including research reference, so you can be sure it’s based on fact, not fads.
Overeating will cause an increase in body fat. No single food or macronutrient is to blame. It’s your overall dietary habits that dictate your long-term progress.
That being said, in the short-term the macronutrient composition of what you eat can influence the amount of fat you gain in a day of overeating.
Contrary to popular belief, carbs don’t turn straight into fat when you overeat. The conversion of excess carbohydrates to fatty acids, which can then be stored as body fat is called De Novo Lipogenesis (DNL). This is an energy expensive process and therefore doesn’t happen to any great extent in humans. The same goes for protein too.
In fact, it’s the dietary fat you consume that is preferentially stored as body fat, when you eat to excess.
“So does that mean I can just eat carbs and protein and not gain fat?”
Eating mainly carbs and protein, while keeping fat as low as physically possible, is a valid short-term strategy for increasing energy intake without gaining body fat. But this is normally used in specific scenarios, such as a structured refeed, lasting 3-7 days.
Sadly, it’s not a strategy you can adopt for the long-term. Fat is an essential macronutrient required for optimal health and hormone production. Therefore, very low fat intake can cause significant health issues.
On top of that, keeping fat very low isn’t as fun as it sounds. Most of the foods you’ll indulge on contain a mix of carbs and fat. So a structured refeed is actually quite restrictive, dull, and boring.
An increase in calories may cause an increase in the amount you move and a short-term reversal of any Metabolic Adaptation you may experience while being in a deficit.
Although, word of caution… Don’t expect to increase calories by 3,000 per day and for that to miraculously be offset by a little extra walking. And everyone’s response to additional calories. After all, you might just crash out on the sofa for hours as a result of a mild food coma.
Most of the calories you consume ARE absorbed by the body, so don’t go thinking this is some form of diet hack. But some foods high in fibre nuts, seeds, and vegetables make it through your system, undigested.
Maybe you’ve heard that the calories absorbed from almonds differs from those stated on the packet by up to 32%. And while this is true, it should affect your approach to understanding and managing energy balance.
However, use the knowledge to understand there are many processes, function, and reasons why not all the calories you consume translate into a body fat increase when you overeat.
The Bottom Line On How To Much Fat You Can Gain In A Day
You can’t defy the laws of energy balance. If you eat to excess, you WILL gain body fat. But how much fat you’ll gain in one day of overeating is hard to predict with any degree of accuracy. However, it’s unlikely to be as much as you think.
An increase in body fat will only happen in a calorie surplus.
How much of an increase is largely unpredictable and driven by a number of factors, mainly related to what and how much you ate. The important thing to remember is that it’s very hard to gain a significant amount of body fat in a single day of eating. Unless you eat like it’s the onset of the apocalypse, any body fat you gain can easily be lost by getting straight back to your calorie deficit as quickly as possible.
So, if you overeat, the best thing you can do is put it behind you and move on. Tying yourself up in knots and punishing yourself is NEVER the right approach.
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