How can calorie restriction even make sense?

I admit that I know as much about how the human body works as your average Philosophy major, but there’s something about calorie restriction that I don’t get.

It seems to me that calories, being units of energy, are going to be stored if you take in too many. Namely, they’ll be stored as fat. If you take in just enough calories, you’ll get through your day without storing more fat. And if you eat fewer calories than you need to get through your day, you’ll take calories out of fat reserves, and maybe lose weight.

I realize that the above simplification may be too simple, but for my question, it suffices. Basically, how can people consistently, in the long run, use a calorie-restricted diet without dying? Your body needs energy to do what it does. So if you consume fewer calories, your body is going to eventually just atrophy. It won’t be able to run anymore.

So am I missing something? How can calorie restriction fail to be anything but an attempt to run on empty?

One factor that you might not have considered is the basal metabolic rate (the calories needed for the body to just sustain itself). Keep in mind that the heavier you are, the more calories you need to consume every day just to maintain all that extra poundage. Calorie restriction causes your body to lose weight, as you mention, but as you do so, your “maintenance calorie” needs are reduced as well, until eventually the two reach equilibrium.

Basically, what counts as a “restricted calorie diet” for a 400lb man is not the same as what counts as a “restricted calorie diet” for a 150lb man.

You are right that I had not quite considered that. However, what you are describing seems like a temporary use of calorie restriction followed by a normal diet.

Suppose I weigh a ton. I could use calorie restriction to lose weight. But eventually, I’m going to have to go off calorie restriction because eventually, I will lose my life by losing weight.

It seems to me that a fundamental part of calorie restriction would not merely be to not have tons of body fat. In order to minimize calorie consumption, one would want to be quite un-muscular. So calorie restriction would require one to forgo both aerobic and anaerobic exercise.

Nope. You’ll just change your restricted amount to match your daily maintenance amount. You’re restricting yourself to the normal amount, otherwise, you’ll gain the weight back.

I am unclear what you mean by “calorie restriction.”

If a person consistently takes in fewer calories than they expend, then they will starve to death.

Could you give me an example of what you are envisioning? I mean, “calorie restriction” is a failrly vague term.

As a personal example, my Wife has lost 65 pounds since February. Her caloric intake is the same today as it was in March, but she is no longer losing weight because the intake is now at the maintenance level for her new body mass and exercise level. And it is still quite a bit lower than the calories I take in (which seems to be a maintenance level for a 6’ 1" 225-pound man, or at least my weight has not changed significantly is a decade).

So in this scenario, my restricted amount is my daily maintenance amount?

Does this mean that, as an out-of-shape thin young man who is not gaining weight, I am technically practicing calorie restriction?

If you really, really want to eat more, then yes you are pracrticing calorie restriction.

There are certain things which I would love to eat more of.

But I have other priorities!

If you were to somehow magically gain 500lbs overnight, then yes, if you continued to eat your current diet, it would count as “calorie restriction.” (your BMR needs would go up, yet your calories consumed would stay the same as they were previously). Thus, you’d probably lose weight every week until you were back to your current weight.

It sounds as though you may be confusing calorie restriction and Calorie deficit. With a unchanging calorie deficit(taking in fewer calories that you use during the day) you will die eventually. But calorie restriction isn’t a problem.

These follwing number are only for relative comparison, and not of actual value for nutrition.

Say a guy has more or less stabilized his life style at 5000 calories a day. And this has stabilized his weight at 400. The doctor wants this guy a 200 pounds. He goes to the doctor and the doctor does some calculations and determines a 3500 calorie a day restriction is the best for this guy. That would be a 1500 calorie a day deficit(ignoring increased exercise).
The guy starts losing weight and at some point his weight has reduced to 350. He still has a 3500 calorie a day restriction. But because of his lost of standing fat cell to support his deficit is lower. (Making a number out of my ass) at 350 his equilibrium point might 4200 calories a day. He is now still having a 3500 a day restriction, but only a 700 C deficit.
As time passes he will continue to lose weight, but at a slower pace as the deficit continues to shrink so the fat burned is lessened. So he hits 300 pounds. Now for example purposes 3500 calories is the equilibrium point for 300 pounds. He has a deficit of 0. But he still has the restriction of 3500 until he dies if he wants, and he will maintain 300 pounds.

In reality a good doctor will check it out at a check up and recalculate. Around 330 pounds or so he might design a new diet at a lower restriction. Because as the deficit gets very low weight loss becomes incredibly slow. AT the 330 pound mark he may set the restriction at 2500 calories a day. again making up nonsense numbers, say the equilibrium intake for 330 Pounds is 4000 calories. He again has a deficit of 1500 on the restriction of 2500.

ANs so on and so forth stair stepping down as the curve flattens until he is at the 200 pound mark on an equilibrium diet of lets say 1700 calories a day. The deficit is then 0 once a again, but the restriction will always be 1700 and never lower, and the weight will be 200.

If the doctor had just thrown the 1700 calorie restriction on in the first place it would have been a deficit of 3300 a day. That would be considered an unhealthy rate of weight loss causing more shock and damage to the body than a slow measured slimming down.

From what I vaguely remember about it from my diabetic nutritionist …

The average person eats too much. Calorie Restriction is actually modifying your diet to that where you consume the baseline amount of food, not restricting below what your body actually needs…

For example, Bob eats 3500 cal a day, like he has every day since high school. He picks his foods more or less at random by what he likes to eat. His body actually only needs 2100 cal to live and be healthy. He may be a marathon runner for fun, so he can manage to eat like that without getting fat.

A restricted diet for him would mean making certain changes in what he actually eats, changing processed crap for whole grains, legumes, vegetable fats instead of animal fats, less sugars, and reducing the calories he eats to 2100 cal.

Some people take it to extremes … there is some guy I found online back in about 2002 or so who makes a single huge salad and that is all he eats 3 times a day, 7 days a week … he has apparently calculated exactly what plants he needs to get whatever chemicals our body needs … but he is scrawny and looks like a stiff breeze would blow him away, and he looks like death warmed over [pale, stringy, thin hair, skeletal body]

Are you referring to calorie restriction for the purposes of weight loss? Or are you confused as to how calorie restriction works in proposed life extention? The former would be a temporary measure that would eventually self correct as your weight levels out. The latter seems to be a far more complicated process involving metabolic changes, hormonal changes, cellular hormesis, and immune system modulation.

I’ve read a lot on the subject and I don’t think there is a firm scientific consensus as to exactly what is happening in CR. I think the idea of avoiding long term, low-level inflammation is a good overall theory. Of course it hasn’t been proven to work in humans anyway, though it has worked in lab controlled populations of rats, rabbits, dogs, and monkeys. There might be a link to ALS in human men who attempt to follow a CR diet longterm. There is also evidence that periodic fasting or very strenuous exercise can mimic the effects of CR without reducing overall caloric intake. It is complicated.

It takes energy for a heavy person to cart their weight around each day.
A lighter person does less work to do the same amount of moving around.
If you restrict caloric intake, you’ll become lighter until you reach the point that your caloric intake matches the amount of energy you expend doing stuff each day.
That point won’t equal zero unless you cut your calories too far and the whole system crashes.
Calories equal work:
1 Calorie = 3087 foot pounds = 4184 joules

I was referring to calorie restriction as a life-extension idea.

The average person need about 11 calories per pound to maintain his weight and provide his engergy

I weigh 175 pounds so I need 1,925 (175 X 11).

If I eat less than that over time I will lose weight. If I exercise greatly I will also need to increase my calories.

Here’s the thing, people are horrible at estimating what they eat and how much exercise they do. Few people get enough exercise to lose weight. In fact by exercising alone you will come off losing about 5 pounds. Unless you change your diet, you simply can’t exercise off enough weight.

People are not built for modern times. We Americans eat three meals a day, but in parts of Africa some communities eat three or four times per week.

In the end it will balance out. I’ve said this before, but you really need to look at all these studies that come out and you’ll see changes in metabolism and the like, do occur but they happen in such small quanities you couldn’t notice.

Humans are animals and look at them in the wild. They don’t eat three meals a day at regulary scheduled intervals. They feast and they starve. An extreme example are crocodiles, which in some areas, they only feed when Wildebeests migrate and the crocs gorge themselves. Some of these crocs only eat really twice a year. Then they live on the fat stored by gorging themselves on Wildebeests and what little fish or whatever they find.

Lions also have this. They get all fat and then the herds move on and for a few months it’s slim pickings till the next herd of animals comes along

So why should humans be different? They aren’t

You can live on a simple bland diet very well. In fact the food stuffs sent to Africa are simply soy based, vitamin enriched, gruels. You simply add water and you can live on that stuff forever, if need be.

Oh, that’s different then.

Mice kept on a just-this-side-of-starvation diet live longer than ones who have enough (or too much) to eat. IIRC.

That could be because of lower insulin production or the suppression of various hormones.

It does not lead to a vigourous or lively lifestyle, as far as I know, but does keep the critters alive longer.

Well, yes. That’s what “starvation” is, and it’s why people die if they don’t eat. I don’t think anybody has ever claimed immunity to starvation!

Reducing calories is one thing; cutting them out altogether will kill you.

As you lose weight, and your body starts to try harder to conserve energy, there’s an efficiency change which means that you need less calories. Obviously that has its limits - there’s only so much you can reduce your calorie intake before it simply isn’t enough to keep you alive, but it is possible to reduce your intake quite significantly, while also (whether deliberately or not - your body will make that decision for you by way of extreme tiredness, etc. - you’ll sleep a lot, you will be too tired to do anything which requires calories, and in this way you’ll use far less) reducing your energy requirement to stay alive.

To an extent, obviously. But the short version is correct - if your calories are permanently below that needed to live, you’ll starve to death.

Except that humans are not (evolutionarily speaking) apex predators; we’re foragers/scroungers (like the other great apes) which have learned to hunt opportunistically, and within the last twelve thousand years. While consumption of meat and animal fats may have been a periodic event for most cultures until the advent of fishing, and later aquaculture and animal husbandry, the consumption of grains, pulses, fruits, and tubers provided a consistent diet for most human cultures. At any rate, binge & fast dieting is the antithesis of calorie restriction, which seeks to maintain a sustainable, consistent minimal calorie intake with balanced micronutrient composition.

On the topic of calorie restriction and it’s alleged advantages to health and longevity, while this has not been extensively demonstrated for people, it has been pretty exhaustively demonstrated in many other mammals, and while the there are several competing (and perhaps complementary) theories, the most widely accepted is that excess calories results in an increase in free radical production and subsequent oxidation damage to both nuclear DNA and mitochondrial (energy producing) structures, especially if not offset by increased physical activity. Calorie restriction reduces metabolic activity and therefore the amount of damage done. It isn’t clear whether there is a significant advantage to extreme calorie restriction (>20% reduction in calorie consumption from recommended levels) versus moderate calorie restriction (<20% reduction), but extreme calorie restriction does appear to have some long term health consequences for at least some people, and obviously results in a reduced ability to support vigorous physical exercise that is widely regarded as being beneficial to long term health.



Calorie restriction as a life extender uses the same principle as calorie restriction for weight loss, the balance point is just set much lower.

Instead of reaching a balance at a 2000 calorie point, you set the balance at 1000 calories, or 800 calories, or whatever. Just enough to sustain but running the body lean.

You do not keep lowering the calorie intake indefinitely - you establish a value and maintain that value.

Whether or not that is actually more healthy has not be established.