Everyone I've ever talked to has said that you will gain some, or a lot of, fat on a bulk.


Logic 1: If you lift weights, your body wants to grow your muscles.

Logic 2: Your body can only grow your muscles if it has the energy + protein to do so.

Logic 3: If you bulk, you are giving your body some energy + protein to build muscle.

So why can't your body just use ALL of the excess food you give it to build muscle, hence adding NO fat to your body?

In fact, why can't your body use MORE than the excess food you give it to build muscle by getting the rest from your fat stores, so that muscle is built while cutting fat?

Example: say your maintenance is 2000 Calories, and you start lifting weights and eating at 2500 Calories. Why can't your body just take those 2500 calories, use 500 of them to build muscle and 2000 of them to keep you alive like it usually did? Then muscles will grow but no fat will be gained?

  • Because dirty bulking is more fun than clean bulking.
    – C. Lange
    Aug 5, 2020 at 21:16
  • That is the norm in bodybuilding circles, but it is an exception elsewhere. And it is more cultural than it is evidence-based. ‘Dirty bulking,’ as it is known, develops muscle more rapidly, but also develops fat which subsequently needs to be ‘cut.’ There is no objective evidence that this practice is more efficient overall. As for what can be done, I have discussed it in more detail here
    – POD
    Aug 5, 2020 at 22:20

2 Answers 2


Naturally, your body tries to get rid of muscle and store fat naturally for survival purposes.. Muscle consumes a lot of calories to maintain, so for survival purposes your body will constantly try to get rid of muscle, and store as much fat as possible. Your body's fat storage also is best used for low intensity, long exercises such as walking or hiking, your body's carbs and glycogen are used for higher intensity exercises and for muscle fuel.

Given the above info, bodybuilding is an attempt to fight your body's basic urges, so eating more calories than needed makes it easy to gain muscle. The hard part is keeping the muscle while focusing on losing fat, because of the way your body's biology works.

You can technically lose fat on a bulk but it requires exact science and a PERFECT diet consisting of PERFECT macro ratios, and the PERFECT amount of exercise. Some bodybuilders also just consume extra calories and go for many long walks throughout the week, I'm talking two hours a day sometimes to cut the extra fat you gain.. but it's difficult. Same goes for cutting, your body is going to think you don't have enough calories or nutrients so the first thing it is going to get rid of after a couple weeks of cutting is your muscle, because it is calorie expensive to maintain. Cutting always loses a little bit of muscle and bulking always puts on a little fat, You can use some science to meet in the middle, or just go on a maintenance diet, but again, unless you're going for long hikes everyday or just have a team of nutritionists planning out your diet to a perfect plan, which is near impossible because even fitness experts cant accurately tell how many calories of lean muscle or pure fat you're going to burn/add during exercise with diet to an exact number, with extra variables such as cortisol, sleep, stress, hormones, ---you can already see how complicated this is getting right? Best thing is to prevent as much fat from accumulating during a bulk as you can, and prevent muscle loss during a cut best that you can.


Your body can only build so much muscle in a given period of time. For example, let’s say your maximal amount is 1kg per month. Do you only gain weight in muscle you only gain 0.5kg that month? Generally, no. Although it wouldn’t be unreasonable to assume that the vast majority of that (say 0.4 kg) would be muscle. What if you gain 2kg? If the maximum amount of muscle you can build is 1kg, logically the rest of the weight you gained must have come from elsewhere- fat.

The best chance you have in losing fat while bulking would be to massively overconsume protein. Protein overfeeding studies have shown such a phenomenon, with one such study being briefly overviewed here. https://www.instagram.com/p/CAFuoHzjRda/?igshid=1sur6ncdynp2s

  • From that instagram post: "There were no significant differences between the 2 groups for changes in body fat". So I am not sure if the conclusion follows? Seems like eating moderately high level of proteins will impact body fat in the same way as those who ate a really high amount. So either way, seems like the appropiate conclusion is to just meet a basic protein minimum of 2x bodyweight in kg, and that will be enough to limit fat gains
    – Jem
    Aug 5, 2020 at 22:47
  • @Jem - The high protein group simultaneously gained more muscle and lost fat. +4 lbs of muscle, - 0.5 lbs of fat. The normal group gained about 3 lbs of muscle and also gained about 0.5 lbs of fat. Statistical significance aside, I would consider that a profound finding. Aug 6, 2020 at 2:02

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