Can/does your metabolism adjust to changes in calorie intake?

[Delayed_Reflex]

I’ve often heard that 3600 calories = 1 pound of fat (most recently brought to my attention in wierdaaron’s post in this thread), but I’ve wondered whether it is just that straightforward.

Suppose your “equilibrium” calorie intake is 2000 calories/day for a given level of daily activity. If you eat 1400 calories/day while maintaining the level of activity, will you lose 1 lb every 6 days (slowing in rate until you reach the weight where 1400 calories/day is your equilibrium calorie intake)? Alternatively, if you maintain a 2000 calories/day diet and expend an extra 600 calories doing physical exercise every day, would you lose the same amount of weight? Mainly, I am wondering:

1. Does your body absorb all the calories that go into your stomach? I understand that some energy is lost in the digestion process, but is any energy typically rejected in waste (not absorbed or used)? Is the “efficiency” of digesting calories typically pretty constant, or does it vary (ie. are you more efficient at digesting if your body is under-nourished vs. over-nourished?)

2. Does your base metabolism change due to your “calorie balance”? Ie. Is your metabolism the same when you are 100 calories over equilibrium vs. 100 calories below equilibrium daily on a regular basis? Or is it essentially purely a property of your weight/height/age/genetics?

I understand that the study of body weight is pretty complex and there are factors like different metabolic rates for fat vs. muscle, but I’ve wondered whether your overall average metabolism ever changes due to differing calorie input situations.

Another somewhat related question is: is there a minimal level of calorie intake required in order for you to survive? Ie. if someone had 100 lbs of fat on them, could they live for weeks just drinking water and eating vitamins? Like a camel

[dracoi]

Your body does adjust its metabolism based on diet. This is why crash dieters often sabotage themselves - as the body reacts to what it perceives as a threat of starvation, it works to reduce its metabolic needs. I have heard reports that the body will actually prefer breaking down muscle tissue to fat in a case like this, as muscle has a higher baseline metabolic need and is a less efficient store of energy.

[barbitu8]

The body cannot convert fat into muscle or vice versa. However, in starvation mode, the body will break down the proteins and use them for energy. This is a last ditch effort to survive. The body normally uses just sugars and fats for energy.

[barbitu8]

My message was sent before I was finished. I wanted to add that camels, as well as people, need more than water and vitamins. We need minerals, essential amino acids (those that we cannot synthesize), fats, and sugars. Fats are necessary for digestion of fat-soluble vitamins and protection of organs. We need amino acids to synthesize proteins.

IIRC, the body needs a mininum of 1200 calories daily to survive.

[Imasquare]

@dracoi

Your body does adjust its metabolism based on diet. This is why crash dieters often sabotage themselves - as the body reacts to what it perceives as a threat of starvation, it works to reduce its metabolic needs. I have heard reports that the body will actually prefer breaking down muscle tissue to fat in a case like this, as muscle has a higher baseline metabolic need and is a less efficient store of energy.

This is a very strange phenomenon.

On the one hand our bodies store excess calories as body fat for use when food is scarce.

But on the other hand, if food is scarce and our calorie consumption drops, the body breaks down muscle tissue instead of the fat that was stored for use in such a situation.

[Claire_Beauchamp]

It’s not that the body doesn’t use fat at all, but that the body – specifically the brain – needs some substances that burning fat can’t provide.

Not only does the body adjust metabolism based on gross caloric input, but also based on frequency of eating. The more frequently you eat, the more revved your engine; the less frequently, the slower. This is also a survival mechanism. If you only get food once a day, or you’re living on roots & berries most of the time with the occasional feast of meat, the body wants to make the most of the situation and store up some of that excess. I’ve heard (never looked into it) that sumo wrestlers only eat once per day to encourage this phenomenon. On the other hand, many if not most diet plans encourage you to eat 4 to 6 small meals per day, at least once every 3 or 4 hours. That kind of frequent feeding is also better for your blood sugar levels.

Another phenomenon is that fat is metabolically not as active as muscle, organs, etc. A 180 pound man with 5% body fat is going to have a faster metabolism than an 180 pound man with 10% body fat. This is one reason men lose weight faster than women. A man and a woman can be the same height and the same weight and the same activity level, but most of the time the man is going to have a higher % of muscle. Thus he can eat more than the woman and not gain, or can go on a diet and eat the same calories she does and lose more weight.

Another factoid is that even if you are eating the right amount of calories to support your metabolism and keep it from dipping, if you lose weight yer gonna lose some muscle. No one loses weight and has it all come from burning fat. Despite the fact that excess fat is unhealthy in some ways, the body sees it as insurance and will work very very hard to preserve it. In women, fat plays an even more important role in hormone levels, fertility, childbearing, breast-feeding, etc.

So, yes, creating a deficit of 3500 calories will cause you to lose one pound of fat, IF your metabolism is exactly, precisely “normal” 24 hours per day. There are lots and lots and lots of variables, though, that cause metabolism not to run at that “normal” pace. If you have no medical issues that might be a factor, eating enough calories to support your base (non-fat) weight, eating frequently, and exercising will all help in keeping it running as high as it can.

[dracoi]

@Imasquare

This is a very strange phenomenon.

On the one hand our bodies store excess calories as body fat for use when food is scarce.

But on the other hand, if food is scarce and our calorie consumption drops, the body breaks down muscle tissue instead of the fat that was stored for use in such a situation.

I don’t think it’s so strange when consider that the body is designed to keep you alive at all costs, not to keep you looking like a supermodel.

Let’s say you have 50,000 calories stored up and that your current metabolism is 2000 per day. If a food shortage cuts your intake to only 1000 per day, you have only 50 days worth of stored calories. But, your body realizes that it could drop a few muscles (most Americans aren’t using those muscles anyway), and reduce your calorie need to, say, 1500 per day. Now you’ve got 100 days worth of stored calories.

Your body thinks it is very clever, since 100 days will get it all the way through winter and into spring whereas 50 days would mean starving to death in February. Your body doesn’t understand that your brain just wants to look good in a swimsuit.

[athelas]

@Claire_Beauchamp

Another phenomenon is that fat is metabolically not as active as muscle, organs, etc. A 180 pound man with 5% body fat is going to have a faster metabolism than an 180 pound man with 10% body fat. This is one reason men lose weight faster than women. A man and a woman can be the same height and the same weight and the same activity level, but most of the time the man is going to have a higher % of muscle. Thus he can eat more than the woman and not gain, or can go on a diet and eat the same calories she does and lose more weight.

Yes, but the impact is very small. The resting metabolic rate of fat is 2cal/day, muscle is 6cal/day. So if you convert 5lbs of fat into muscle (no small achievement!), you’ll burn an extra…20 calories per day.

Does anyone know of a reliable and comprehensive website for these fitness/weight loss issues?

[Imasquare]

@dracoi

I don’t think it’s so strange when consider that the body is designed to keep you alive at all costs, not to keep you looking like a supermodel.

Let’s say you have 50,000 calories stored up and that your current metabolism is 2000 per day. If a food shortage cuts your intake to only 1000 per day, you have only 50 days worth of stored calories. But, your body realizes that it could drop a few muscles (most Americans aren’t using those muscles anyway), and reduce your calorie need to, say, 1500 per day. Now you’ve got 100 days worth of stored calories.

Your body thinks it is very clever, since 100 days will get it all the way through winter and into spring whereas 50 days would mean starving to death in February. Your body doesn’t understand that your brain just wants to look good in a swimsuit.

But wouldn’t consuming muscle tissue in preference to fat make it harder to go out and hunt down something to eat?

[aruvqan]

@Claire_Beauchamp

In women, fat plays an even more important role in hormone levels, fertility, childbearing, breast-feeding, etc.

.

So … just having had a hysterectomy with the ovaries removed is my body perhaps not going to try and keep that deathgrip on the fat in my cells? Will it make it a bit easier to get rid of it metabolically? Being a nonexercising gimp has its downfalls =(

[wierdaaron]

@athelas

Yes, but the impact is very small. The resting metabolic rate of fat is 2cal/day, muscle is 6cal/day. So if you convert 5lbs of fat into muscle (no small achievement!), you’ll burn an extra…20 calories per day.

Does anyone know of a reliable and comprehensive website for these fitness/weight loss issues?

According to that link, your heart burns 200 calories per pound per day. So the ideal weight loss solution would be to have 2 or 3 extra hearts installed.

[barbitu8]

@athelas

Yes, but the impact is very small. The resting metabolic rate of fat is 2cal/day, muscle is 6cal/day. So if you convert 5lbs of fat into muscle (no small achievement!), you’ll burn an extra…20 calories per day.

Does anyone know of a reliable and comprehensive website for these fitness/weight loss issues?

This is the same misconception the author of a recent Time article made. Muscle and fat are made up of different components and you cannot convert one into the other. You lose fat by expending more calories than you intake. You gain muscle by exercising the muscle. So, if you lose 5 lbs of fat, you lose 5 lbs of fat. You have not converted that into muscle. If, at the same time, you work out and develop a certain muscle or muscles and gain 5 lbs of muscle, your net weight will be the same. But you’ve lost fat and gained muscle, a more metabolically active tissue and better for you all around. That’s not to say that fat is not necessary. You need fat for digestion of fat-soluble vitamins, protection of internal organs, secretions of some hormones, etc.

Your body will burn fat before it will use protein, which is done only in starvation diets. Sugars is the preferred compound for energy and fat is second. Protein conversion into energy is much more complex and is not done easily.

[athelas]

@barbitu8

This is the same misconception the author of a recent Time article made. Muscle and fat are made up of different components and you cannot convert one into the other. You lose fat by expending more calories than you intake. You gain muscle by exercising the muscle. So, if you lose 5 lbs of fat, you lose 5 lbs of fat. You have not converted that into muscle. If, at the same time, you work out and develop a certain muscle or muscles and gain 5 lbs of muscle, your net weight will be the same.

Yes, but nevertheless, my point is that your baseline metabolic activity is virtually unaffected.

[dracoi]

@Imasquare

But wouldn’t consuming muscle tissue in preference to fat make it harder to go out and hunt down something to eat?

But if you go out and hunt, you’re exercising. Exercising maintains the strength of muscles. That’s why I specified that the burning of muscle was due to 1) starvation diets, with 2) lack of exercise. (And it’s why even the least healthy diet in the world is still smart enough to say “with exercise” when discussing the results.)

However, you still have to think about it from a survival standpoint. If you’ve gone three months on a starvation diet, why would your body believe that the next hunt is going to be any more successful than the last 90? Heck, someone in an extreme case of starvation actually suffers atrophy of their digestive tract to the point that eating a large meal quickly will kill them.

The body’s starvation response is not geared toward health; you’re starving, health is already out of the question. The response is geared toward keeping you at least marginally alive for as long as possible, regardless of the consequences.

[glowacks]

@dracoi

The body’s starvation response is not geared toward health; you’re starving, health is already out of the question. The response is geared toward keeping you at least marginally alive for as long as possible, regardless of the consequences.

One thing to keep in mind when discussing this from an evolutionary biological standpoint is that men don’t need huge stores of energy to reproduce - but women do.

[Delayed_Reflex]

@barbitu8

This is the same misconception the author of a recent Time article made. Muscle and fat are made up of different components and you cannot convert one into the other. You lose fat by expending more calories than you intake. You gain muscle by exercising the muscle. So, if you lose 5 lbs of fat, you lose 5 lbs of fat. You have not converted that into muscle. If, at the same time, you work out and develop a certain muscle or muscles and gain 5 lbs of muscle, your net weight will be the same. But you’ve lost fat and gained muscle, a more metabolically active tissue and better for you all around. That’s not to say that fat is not necessary. You need fat for digestion of fat-soluble vitamins, protection of internal organs, secretions of some hormones, etc.

Your body will burn fat before it will use protein, which is done only in starvation diets. Sugars is the preferred compound for energy and fat is second. Protein conversion into energy is much more complex and is not done easily.

I’m not sure if when people say they are “turning fat into muscle” they mean that you are literally transforming fat cells into muscle cells - just that by exercising you are building your muscle and burning energy, which under certain circumstances may result in burning fat.

@Claire Beauchamp

Another factoid is that even if you are eating the right amount of calories to support your metabolism and keep it from dipping, if you lose weight yer gonna lose some muscle. No one loses weight and has it all come from burning fat. Despite the fact that excess fat is unhealthy in some ways, the body sees it as insurance and will work very very hard to preserve it. In women, fat plays an even more important role in hormone levels, fertility, childbearing, breast-feeding, etc.

Interesting - I never really thought about other reasons that the body would want to keep fat around other than as energy storage (packing snacks, one could say). Still, I do wonder where that balance is struck between reducing your metabolism to save energy and burning fat to obtain energy in starvation situations.

[barbitu8]

@Delayed_Reflex

I’m not sure if when people say they are “turning fat into muscle” they mean that you are literally transforming fat cells into muscle cells - just that by exercising you are building your muscle and burning energy, which under certain circumstances may result in burning fat.

I have to believe that people mean what they say.

Interesting - I never really thought about other reasons that the body would want to keep fat around other than as energy storage (packing snacks, one could say). Still, I do wonder where that balance is struck between reducing your metabolism to save energy and burning fat to obtain energy in starvation situations.

Fats are burned not only in starvation situations, but also in aerobic exercise. In fact, you never use just glucose for energy, but also use some fats. That is why caffeine is an ergogenic aide: it helps the body use triglycerides for energy. You need oxygen to burn fat, but no to burn glucose, but no exercise is strictly anerobic.

In addition, fat serves other useful purposes: It is necessary to digest fat-soluble vitamins; it secretes some hormones and it protects internal organs.