How much fat can you gain in one day according to science

It's not healthy, or realistic, to expect to gain a significant amount of weight in one day. It takes more than you actually think. In saying that thought, the amount of weight you can gain in a day, or a week, depends on many factors, including your diet, activity level, and overall health. On average, a person can gain 0.5-1kg in a week, but this can vary greatly.

For many years science has given us a simple answer - to put on one kilogram of weight in a week, a person would need to consume an additional 7700 calories on top of their daily energy requirements. This is equivalent to consuming an additional 1100 calories per day for a week, MORE than is needed to maintain your current weight.

But this is an average, and that's not good enough for me, I wanna know more. Because you're reading this, I'm going to assume you do too. So let's see what the science says.

I'm not going to bore you with the details so here is the summary of what the studies say:

Let's look at this study conducted by scientists at the University of Colorado. The researchers fed 16 men 50% more calories than they needed to maintain their weight every day, which turned out to be around 1,400 extra calorie per day. 

After two weeks of this overeating they gained 1.36kg of fat. That works out to 680g of fat per week, or 90g per day.

Our next study was conducted by scientists at the Pennington Biomedical Research Centre. 

Twenty-nine 'slightly' overweight men ate 40% more calories than their maintenance calories for 8 weeks. This worked out to be around 1200-1500 calories of surplus per day. At the end of the study the researchers found they gained on average of 4kg, which works out to be 0.5kg per week, 72g per day.

Now I didn't want to tell you this to scare you, these studies were over many weeks of overeating.

If you go out for your birthday, or an event every now and then and go HARD on the all-you-can-eat buffet, you aren't going to wake up unable to fit into your jeans. Our bodies have certain mechanisms to stop fat gain in an acute overfeeding session. 

To put on weight you would have to eat over your maintenance calories over a period of time. Our bodies don’t work on day to day calories, it works on averages over time. Which means if your weekly average calories are over the amount of energy your body needs for day to day movement/activity you will gain weight.

But Kristy, I ate over my calories and the next day I was 2kg up on the scale.

If you eat more than usual, STEP AWAY FROM THE SCALES the few days after.

If you're heavier the few days after eating more then usual, there’s a few things happening in your body to cause this, that is NOT fat gain.

One is the increase in sodium. If your meal was heavy on the sodium you will be experiencing some water retention. To combat this, drink a few extra glasses of water to help flush the sodium out of your system, and decrease that water weight.

Just like sodium, carbs can also cause water retention. When your body stores carbohydrates, it binds to water molecules at a ratio of 1 gram of carb to 3 to 4 grams of water. In layman's terms, for every gram of carb your body will retain 3-4 grams of water. So if you’ve eaten a high carb meal that night, the next day your body will be retaining more water than usual. Which again means ‘weight’ on the scale, masked as fat.

Let’s also mention the actual weight of having more food than usual in your colon, which again causes more weight when you step on the scale. 

We’re all adults here so I also want to mention when you do a poo, a poo can actually weigh a bit, and, if you haven't yet gone to the toilet, you may see the weight reflected on the scale. 

Just to top it off, you probably ate later than usual which again adds to the scale weight.

So don’t stress - if you needed a “treat yo self” kinda night go for it (in moderation). My main message here is not to sweat the small stuff. If you have a night of overindulging don’t beat yourself up - just get back on track the next day. In saying that though, if you overindulge often enough you can gain weight because going over your daily calories does add up over time. 

As always, everything in moderation!

Have you been overindulging over a period of time and put on a few unwanted kilograms? Click here to find out how we can help you!