How Much Weight Can You Gain in a Day?

High angle of a woman standing on a scale

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Have you ever wondered if there is a limit to how much weight you can gain in a day, no matter how many calories you eat?

Calories and Gaining Weight

If you do the math, you need to consume an extra 3,500 calories to gain 1 pound of fat. A pound of fat translates into more bodyweight because you gain water weight in addition to fat. But, given that your stomach can only hold so much food at a time, there is a practical limit to how many calories you can consume in a day.

If that day is Thanksgiving, for example, you're actually filling up on some foods that aren't incredibly high in calories. You're eating a combination of food, not just pure fat, which would be your quickest route to high calories. This means it's unlikely you'll take in more than 10,000 calories, regardless of how determined you are to feast until you can't eat anymore.

That translates into a couple of pounds, at most, because you're burning calories while you're consuming them. If the meal is high in sodium, you may retain additional water weight, but you'll shed that over the next couple of days, assuming you return to your normal eating habits.

You Can Only Gain So Much

Another factor to consider is that you only produce a certain amount of the enzymes needed to digest your food. You won't meet that limit by eating a normal, large meal, but there is a limit to how much of any nutrient you can process and absorb.

You also have your metabolism to consider. If you severely restrict calories, your metabolism adapts so that you can burn them more efficiently. Eating too many calories can have the opposite effect, revving up your metabolism as part of a physiological process to maintain a "set point."

Whether you can alter your metabolism with a single day's change is debatable, but even competitive eaters don't necessarily gain weight. If you do gain weight, most of it will be water and fat, since it takes time to add more muscle mass. Also, you can increase your metabolism on your own by increasing your activity level.