Does Body Fat percentage effect your metabolism?

A group of folks on here will give you an approximation if you ask them. They will want several shots and they are fairly accurate with their estimates. Just search the thread and contact them.

As for metabolism, I have no idea. I've dropped from 30.3 to 21.8 in body fat and could care less about resting metabolism as long as the body fat drops I'm a happy camper. Best of luck.

Generally as you lose weight a combination of things happen:

1) You have less weight to move around, which causes you to burn less calories.
2) An adaptive response to dieting occurs (combination of hormonal downregulation, reduction in spontaneous activity) that further reduces your caloric expenditure.

EDIT: But I don't think it's a cut-and-dry issue. For example if an obese sedentary individual lifts weights and diets down to a reasonable level of leanness and continues to train hard (I'm speaking in terms of years here, not days), I wouldn't be surprised to see an increase in total expenditure when you factor in the contribution from LBM and the massive upswing in activity going from "sits on the couch" to "trains like a beast".

And I only mention the latter part of it for context.

the best way to think of this question, is that all the cells in your body need energy. so, more cells = you need more energy (higher basal metabolic rate (BMR)) = your metabolism is faster

however, different cells need different amounts of energy. muscle cells and brain cells need a lot of energy, fat cells not so much, because they're just sitting around doing not so much, while your brain cells and muscle cells are working hard.

so to answer your question more specifically....

if the body fat percentage has gone up because you gained muscle mass, then your metabolism will be faster, because more muscle cells = you need more energy to keep the new cells going = faster metabolism

however if your body fat percentage has gone down because you lost fat, then your metabolism will slow, because fewer fat cells = you don't need quite so much energy to keep all your cells alive. but fat cells don't burn as much as muscle, so the decrease in metabolism from fat loss is smaller than if you'd lost the same number of muscle cells.

if both have happened (which can happen with noob gains etc), then the new muscle cells will be using more energy while the newly shrunk fat tissues will be using less energy. So your metabolism may be a bit faster or a bit slower, depending on the proportions of muscle gained to fat lost.


Another angle to approach this question.... say you have two people of the same weight, but one has a lower body fat percentage than the other, the one with the lower body fat percentage would be expected to have a faster metabolism, because they have proportionally more lean mass (which includes more cells that work hard and burn more energy) and proportionally less fat (fat cells don't burn that much energy.

There are other factors that affect the metabolism though, i.e. medical conditions, medication, the human body's adaptations to prolonged food shortages (i.e. prolonged insufficient food intake) can all affect the metabolism as well.

One thing to realise though, is that the above things will result in small changes in the metabolism, if you are aiming to maximise the amount of calories you burn, then exercise and physical activity will burn far more than changes in your body composition (e.g. adding more lean mass) will. However they're not mutually exclusive... you can do both, i.e. increase your lean mass and increase your activity levels. And also, eat properly. I hate the term "starvation mode" but millions of years of evolution in favour of individuals who can survive food shortages, means that the human body is very good at adapting to insufficient food.... good news if you want to survive a famine, bad news if you're trying to lose body fat.

The amount of lean muscle you have does affect your RMR. Look up the Katch-McArdle formulas for more information. I know I had my RMR tested and it was extremely close to the calculated RMR. For those that say it doesn't matter, I disagree. My RMR is 1580 calories/day (at 128 lbs and 19% BF). That adds into the overall amount I can eat. And since I do like food...

generally speaking, your body does NOT like being lean.

Simple but perfectly put!

Absolutely....and I base this answer on emperical data! Two years ago I had by RMR tested by my doctor, you know, machines and all, and they determined that I was below average and that I needed to eat below 1200 if I wanted to lose weight. I have spent almost two years working at losing weight and working out and increasing my muscle mass and reducing my body fat. I had my RMR retested last week, and I am happy to say that according to the test, I need to eat 2000 calories just to maintain my weight, and I shouldn't eat any less than 1500 calories! I hope this helps!

The leaner you are, the less calories your body needs to maintain itself.

I believe you mean more.

I'm much leaner than I used to be and I require fewer calories to maintain my weight than I used to simply because I weigh about 40 Lbs less. When I was fat I could maintain eating more calories than I do now and I didn't exercise...now I have to exercise just to be able to approach the amount of food I used to eat...and it's still not that close.

That said, and I think I explained it...I'm about 180 Lbs and 19% BF...someone of the same stats but being 12% BF would actually require more calories because body weight is the same...but LBM would be substantially more.

You require fewer calories because you have 40lbs less mass, not because you are leaner.

At a given weight, the leaner body will require more calories to maintain than the less lean body (all else being equal).

So the correct statement is "The leaner you are, the MORE calories your body needs to maintain itself."

The less you weigh, the fewer calories you need to sustain your body weight and fuel your activity. The more you weigh, whether it's fat or muscle, the more calories you use to do the same things. Beyond that, there are no simple, uncontested answers.

This is just my personal experience, but it appears that I need to eat a lot more than most people that are the same size as me. If I don't, then I lose weight very rapidly that I don't want to lose. I still want to be lean, fit, with a good body composition. Lifting weights helps me to keep weight on in a sense because then I can maintain and build muscle. It seems the leaner I get, the more food I need to eat. I can eat less when my activity level decreases, but that usually only happens if I am dealing with something that is depressing (being active is an important part of my life).

^ This and what johnnythan said.

If someone is heavier and losing fat + muscle with just eating at a deficit, they will need gradually less calories and have a lower RMR.

If someone is dropping body fat % but increasing (or even maintaining) a higher LBM than the first person, their RMR will be higher in order to maintain muscle.

It's hard for the body to maintain a low bf%+LBM than it is to maintain a higher body fat %, and that "hardness" requires calories and work (strength training, activity, etc.).

generally speaking, your body does NOT like being lean.

Simple but perfectly put!

I think everyone is different, and probably mostly has to do with genetics. I have always been fairly lean and so has my father. It is just our body type.