Does metabolism slow down as you lose weight?

[iamfit]

I want to lose 15 pounds. From what I understand, the underlying cause of weight gain or weight loss is a difference in how many calories your body can burn versus how much you put in. Whatever that number is, say 3000 per day, if you ate 3000 calories per day, you would stay the same weight. The rate at which your body burns the calories is called metabolism. Fast metabolism will burn a higher amount of calories where a low metabolism would burn less calories over a period of time. As far as the research I’ve done, that philosophy seems to be universally believed to be true. Right?

So my question is, if I’ve found out what that magic number is for myself, does it matter what my current weight is? Does that change the number?

More specifically, I’m a male, 30yrs old, 5’11” 190 pounds. If my number is 3500 calories per day. So basically if I eat a diet everyday of 3500 calories I will not gain or lose weight. I’ll stay at 190. But, let’s say I decide I want to lose 15 pounds. Then I would start eating only 3000 calories a day and over a period of a couple of months I would drop down to 175 pounds.

Here’s where I don’t understand: Other things I’ve read they always say “as soon as you go back eating the way you were before the diet, you’re going to gain all that weight back”. Why is that so? Is your metabolism slower once you are at a lower body weight? Why would all of the sudden start gaining weight if you went back to eating 3500 calories per day? Wasn’t that the magic number that keeps you the same weight? Why is your new number all of the sudden lower?

Sorry for the long explanation. I hope understand what my underlying question is. Thanks,

 

[SonofJorEl]

The "problem" in answering your question is the existence of so many extraneous variables..

Exercise, activity-level, eating habits, etc...these variables factor in tremendously to your question IMHO..

I guess my answer (which is not worth much admittedly) would be:

Assuming that your levels of activity before the weightloss and after are very similar...and that the types of food you eat are also...

I'd say a body at 210 lbs. per se' would need more calories to maintain itself than a 190 lb body..

But again...that's assuming EVERYTHING else is equal...as far as muscle, exercise...etc...

JMHO

 

[iamfit]

Thanks for the quick response. I do realize that there are a number of other factors involved but i'm just referring to the specific factor of calorie intake versus calories burned and how that is determined by your metabolism rate. Assuming all other factors are constant. I've just always heard that after everything is accounted for, that is really the only definition of how your body actually loses or gains weight.

It just isn't intuitive that when you're at a lower weight, you need to eat less than someone at a much higher weight to stay at the same weight. You'd think the thinner guy would have a faster metabolism. In otherwords, say there's a guy that's 500 pounds. He's been 500 pounds for a couple of years. He eats 25,000 calories a day. That would mean his metabolism, at 500 pounds, burns 25,000 calories a day. He's probably not moving around much and has low activity. How come my metabolism is 8 times slower than his?

It seems like there is another factor that goes up or down the more or less you weigh. Almost like you have to eat more just to "maintain" that weight, the heavier you are.

 

[Steve]

It just isn't intuitive that when you're at a lower weight, you need to eat less than someone at a much higher weight to stay at the same weight.

Sure it is.

Tissue is metabolically active. The more of it you have, the more energy your body will require to maintain itself.

Not to mention the heavier you are, the more energy you expend moving around.

You'd think the thinner guy would have a faster metabolism.

You can't categorically say "thinner guy."

A naturally thin person who has always been thin most likely does have metabolic features (high rate, fidgets more, etc) than a fat guy.

But a person who is thin after an extended period of dieting down from fatness most likely has some metabolic slowdowns. a) energetic needs are lower since he doesn't have to maintain as much tissue and isn't moving around as much weight and b) there is an adaptive response to dieting relative to metabolic rate.

 

[iamfit]

That does make sense, thank you Steve. So since your body tissue itself metabolizes the calories into energy the body can use...the more body mass you have, the more calories you have to take in just to maintain it. In other words, generally speaking without taking into account other factors...the bigger you are, the more calories you burn per day and vice versa for the smaller you are.

That's why if I lost 20 pounds i couldn't continue to eat like i do now because i have more weight on my body now and therefore burn more calories than i would if i lost 20 pounds? Is that right?

 

[LowFatMilk]

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That's why if I lost 20 pounds i couldn't continue to eat like i do now because i have more weight on my body now and therefore burn more calories than i would if i lost 20 pounds? Is that right?

But have you considered building muscle? You need a calorie surplus to build muscle then too I believe, in which case you'd have to eat extra calories then to build the muscle.

 

[Doc Bunkum]

In other words, generally speaking without taking into account other factors...the bigger you are, the more calories you burn per day and vice versa for the smaller you are.

No, I don't believe you can say that categorically without taking into account body composition.

The caloric requirements of a pound of muscle and pound of fat at rest are different.

A pound of fat requires 2 calories per day to self-sustain (fat while not technically active, has blood vessels and some small scale functioning that takes place within the tissue as part of its maintenance activity) and muscle required 6 calories. (McClave - 2001)

Take two people at 200 lbs - one muscular the other fat. The fatter person will appear bigger simply because he has more surface area.

But the "smaller" muscular person will burn more calories because he has more lbm to maintain.

If I read what you wrote correctly.

 

[iamfit]

OK, I get it now. I didn't realize that body mass itself had an effect on your in/out calories but it makes sense now. Also good to know that more fat will only slightly raise your metabolism (and only to support the fat itself) but muscle raises your metabolism rate 3x faster and it's going to support a good cause, keep muscle.

How does your body choose what to sustain first? Muscle or fat? I've been working out upper body a lot and noticing muscle gain but not really noticing the belly going down. If i start dieting more will my muscles get smaller because they don't have enough energy or will my body burn the fat first?

 

[Doc Bunkum]

How does your body choose what to sustain first? Muscle or fat?

That's a very involved question. In the case of extreme calorie restriction (read wacko diet), the body gives up muscle tissue first, as I understand it.

The reason is simple. Muscle is metabolically active tissue as noted above. So the body will lower its metabolism and try to use as little energy as possible. In doing so, the body will break down more muscle than fat since your body is trying to minimize using energy (less muscle = less calories burned).

Then too the brain needs glucose to stay alive. If it isn't getting sufficient from your diet, then muscle is broken down to provide amino acids that are converted to glucose by the liver and kidneys. The brain can run on ketone bodies derived from fat, but this is getting too complicated.

But with a mild reduction in calories slightly below maintenance, adequate nutrition, and sufficient exercise, you'll minimize skeletal (voluntary muscle) muscle loss. (Obviously the body doesn't cannibalize smooth (involuntary), or cardiac muscle or it couldn't survive).

I've been working out upper body a lot and noticing muscle gain but not really noticing the belly going down.

Generally you lose fat inversely to the way you gain it - first on, last off. You start to get fat around your waist, hips, thighs first. And that is the area that as a rule is the last to give it up.

If i start dieting more will my muscles get smaller because they don't have enough energy or will my body burn the fat first?

Your muscles will get smaller if you don't include enough protein in your diet for repair. Once your protein levels are high enough to maintain/build muscle mass, then they start to use stored fat as fuel/energy. Of course, the amount is dependent on the type of exercise.

Your muscles will get smaller too if you don't get sufficient rest and give them a chance to grow. Most beginners way over train and don't get the results they should.

I'll let Steve jump in here with more specifics. I tend to generalize a lot.

 

[txsqlchick]

But a person who is thin after an extended period of dieting down from fatness most likely has some metabolic slowdowns. a) energetic needs are lower since he doesn't have to maintain as much tissue and isn't moving around as much weight and b) there is an adaptive response to dieting relative to metabolic rate.

Can someone who has become thin after dieting and exercising hope for their metabolism to increase...speed up...whatever the appropriate term is...over time as the body gets used to its new size?