ELI5, what happens when you consume more calories than you use, if you are working out? Do you gain weight as muscles, fat or both?


ELI5, what happens when you consume more calories than you use, if you are working out? Do you gain weight as muscles, fat or both?

In: Biology

If you follow a progressive overload program then yes, some of the extra calories / nutrients will be used for muscle repair / growth. As you lift heavier / more reps, etc, you’re signaling your body to get stronger / bigger to make the lifts easier.

How much of that calories / nutrients get turned into fat deposit or used for muscle growth / repair is heavily dependent on your genetics.

Just to be clear, genetics only matters if you’re looking to be the next fitness model or IFBB Pro. Anyone can look amazing with proper training, diet and consistency over 5-10 years.

That’s called a caloric surplus and is generally necessary for muscle growth. Coupled with u/hiyo3d’s comment on progressive overload your calories have to have enough protein in your macros. Depending on your body fat percentage you’ll want to consume 1.2 to 1.5 grams per pound of Lean Body Mass (body weight less body fat percentage)

How your macros pan out and how much weight you lift (and how often) will determine if you gain fat or muscle

The extent of the calorie surplus is important as well in determining the composition of the body mass increase; there are diminishing returns at which point adding further calories to your surplus will not result in more lean contractile tissue and will instead be fat. This is dependent on your genetics, compound usage, diet model, and how effective / stimulating your exercise programme is.

Eli5 answers – yes, muscle weighs more than the same volume of fat, people who lose fat but put on muscle can actually gain weight. Might not be very common but is technically possible.

Lets change around your question slightly to read “What happens when your body absorbs more calories than it uses.” Remember that not everything you eat is digested and absorbed, and some people may absorb less calories from a given amount of food than other people. So it’s more about how many calories a persons body absorbs (even though most of what they eat is absorbed).

That being said, it depends on you. If you have recently been fasting, or haven’t ate in several days, the excess calories will probably go immediately to restocking the liver with glycogen, which is your primary source of ‘fast’ energy.

The liver has several functions but one of the most important for calorie maintenance is that it acts like a kind of battery, storing energy it can quickly deploy to the body. For instance your liver is what is powering your body between meals (muscles also store local energy for muscle needs) , when you’re sleeping, etc. However the liver has a finite amount of energy it can store. Once it’s exhausted, it needs to be replenished either by eating, or by burning fat through a process called ketosis.

This is why the first day or two of a diet are so hard, because the body isn’t actually dieting yet, it’s just burning energy stored in the liver, hoping you’re going to eat soon. Then when you don’t, it finally starts ramping up fat burning production to start replacing the lost energy. Until it switches to fat burning mode, you’re feeling weak and jittery.

Anyway, say your liver is already topped off, then most likely your excess calories are going to get stored as fat. “But won’t some of it be used to rebuild muscles and bones etc?” yes but you said if you have calories that are more than you need, so if the needs of muscle and bone repair have already been met, and you take in more calories, it’s going to be stored as fat. The body doesn’t really have a strategy for storing long term energy as protein or carbohydrates. It stores short term energy in the liver and muscles, but all long term energy is fat.

Eventually if you’re starving to death long enough, the body will start breaking down your muscle mass for energy as well, but that’s not really because it uses muscles to store long term energy, so much as an emergency crisis because you ran out of fat and you’re starving to death.

Technically, no matter what, if you consume more than you use, you will get fat.

The catch being that you are using some to build/repair muscle. More than that will become stored fat in the body. If you’re working out really hard, it’s less likely to consume too many excess calories though. Kind of depends on genetics and such.

Your body is blind pull system.

It’s not going to pre-allocate all excess calories to muscle building and any more overages to fat.

The muscle building will be signing for resources while the body also does what it normally does with excess calories…make fat.


How much depends on a few things.

1. Training age. If you’re a beginner, you can gain more lean mass. As you get more advanced, your muscle gain will slow down.

2. Training efficacy. Some people are actually training, but a lot of people are “working out.” This is something the typical redditor on r/fitness does. They skip sessions, are constantly deloading to “work on form”, and are hopping from one program to another. These people have poor progress.

3. Calorie surplus. If you’re eating a 200 kcal surplus, then it’s more likely that most of that will be going toward muscle. If you’re eating a 2,000 kcal surplus, you will get very fat.

4. Other. This is things like genetics, meal and nutrient timing. I guess anabolics can be indexed here as well.

Only extreme amounts of ‘working out’, including muscle building, will balance any surplus of kcal intake.

This also makes weight loss efforts difficult as it becomes harder to measure your drops in weight along with gains in muscle weight. I’d encourage a cut first to a goal weight, no muscle building, then it becomes much easier to track progress to that goal weight. Then from there you could bulk for building muscle.

Keep in mind the BMI is source agnostic; fat and muscle weigh something and load your joints and heart. Gravity is unkind to both, its not healthy