The Science of Why Caloric Restriction Fails

Dr. Jason Fung
Jun 9, 2017 · 8 min read

The noted scientist Ancel Keys, who would later play a crucial role in shaping current nutritional orthodoxies, sought to study the effects of caloric reduction in the famous Minnesota Starvation Experiment, published in 1950. With World War II raging, many millions of people were on the verge of starvation and this experiment was an attempt to understand the effects on the human body.

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One of the first problems was finding volunteers. As an alternative to going to war, conscientious objectors were recruited (I think they weren’t volunteering as much as they were ‘volun-told’). Eventually, 36 such ‘volunteers’ participated in this study.

Ancel Keys estimated that these subjects were eating roughly 3,200 calories per day. They were put onto a ‘semi-starvation’ diet of 1,560 calories per day with foods similar to those available in war-torn Europe at the time — potatoes, turnips, bread, and macaroni. They were then monitored for 20 weeks after the semi-starvation period.

What happened to them? Here, we can divide the effects into physical and psychological effects.

Physical effects

Resting metabolic rate dropped by 40%. Interestingly, this is not that far off from a previous study from 1917 that showed Total Energy Expenditure (TEE) decreased by 30%. In other words, the body was shutting down. Let’s think about this again from the body’s point of view. The body is accustomed to getting 3,200 calories per day and now it gets 1,560. In order to preserve itself, it implements across-the-board reductions in energy.

The heart gets less energy — heart rate slows and heart volume shrinks. Blood pressure drops.

The heating system is turned down — body feels cold.

Muscles get less energy — physical exhaustion.

Hair and nails get less energy — hair loss and brittle nails.

The key to remember, though, is that this ensures survival of the individual during a time of extreme stress. Yeah, you might feel lousy, but you’ll live to tell the tale. This is the smart thing for the body to do. It is not so stupid as to keep burning energy it does not have.

Consider the alternative. The body is used to 3,200 calories per day and now gets 1,560. The body still burns 3,200 calories. Things feel normal. Three months later, you are dead. It is absolutely inconceivable that the body does not react to caloric reduction by reducing caloric expenditure.

Consider many statements to the effect that if you reduce 500 calories per day, you will lose one pound in one week. Does that mean that in 200 weeks you will weigh zero pounds? It is clear that at some point, the body must, must, must reduce caloric expenditure. It turns out that the adaptation happens almost immediately and persists in the long-term. More about this later.

Psychological effects

Consider the last time you tried to diet by reducing calories and portion size. Does any of this sound familiar? Yeah, thought so.

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What happened to their weight after the semi-starvation period? Along the x-axis we have the 24 weeks of the starvation period (0 — S24). Both body weight and body fat dropped. As they started upon the recovery period, they regained the weight. Actually, the weight was regained rather quickly — in about 12 or so weeks, the weight is back to baseline.

However, it does not stop there. You can see that the body weight continues to increase until it is actually higher than it was before the experiment started. And just look at that body fat! It goes soaring above baseline. Sound familiar? Thought so.

Let’s review what happens when you go on a calorie restricted, high carbohydrate, low-fat diet of 1,560 calories/day — just like your doctor or dietician currently tells you to do. You feel lousy, tired, cold, hungry, irritable, and depressed. That’s not just because you are dieting, there are physiological reasons why you feel so crappy. Metabolic rate drops, hormones make you hungry, body temperature drops, and there are a multitude of psychological effects. The worst thing is that you lose a bit of weight but you gain it all back when the diet stops.

It is increasingly clear that one of the key assumptions of the Caloric Reduction as Primary theory is incorrect. The Energy Balance Equation says this:

Fat Gained = Calories In — Calories Out

However, you cannot, from this equation, say that reducing ‘Calories In’ results in Fat Loss UNLESS ‘Calories Out’ remains stable. This assumes that ‘Calories In’ is completely independent of ‘Calories Out’. THIS IS NOT TRUE. The caloric expenditures and caloric intake are inextricably linked to each other.

Said another way — reducing Calories In reduces Calories Out. Reducing caloric intake inevitably leads to reduced caloric expenditure. That is why conventional dieting as we know it does not work. I know it. You know it.

Actually, we have known this to be true since 1917. In fact, in our heart of hearts, we probably have always known it to be true. Eating less for a prolonged period makes you tired and hungry. And worst of all… you regain all the weight you have lost. Weight lost is muscle and fat. Weight regained is all fat.

We have just chosen to forget this inconvenient fact because our doctors, our dietitians, our government, our scientists, our politicians, and our media have all been screaming at us for decades that it is all about ‘Calories In vs. Calories Out’. Caloric Reduction is Primary. Eat less, move more, and that kind of idiocy.

We need to completely re-think our conventional view of obesity.

Let’s now fast forward to the modern era, and look at this study published in the prestigious New England Journal of Medicine.

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Changes in Energy Expenditure Resulting from Altered Body Weight
Rudolph L. Leibel NEJM 1995 march 9, 332 (10); 621–28

In this experiment, 18 obese and 23 non-obese subjects with a stable weight were recruited. They were fed a liquid diet of 45% carbohydrate, 40% fat, and 15% protein until the desired weight loss or weight gain was achieved.

One group targeted a 10% weight loss and the other group targeted a 10% weight gain. After weight gain, subjects were then returned to their initial weight, and then a further 10% or 20% weight loss was achieved.

The question they wanted to answer was what happened to TEE when weight was increased or decreased. This was achieved without a change in the composition of the diet. That is, the liquid diet was a constant ratio of carbohydrates, fats, and protein. The only variable was the total intake of this liquid diet. What happens to TEE when caloric intake is varied?

In other words, if we reduce or increase our Calories In, what happens to Calories Out? According to the conventional Caloric Reduction as Primary (CRaP) hypothesis, as Calories In go up or down, there should be not much change in the Calories Out.

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What happened? In the 10% weight gain group, people increased their energy expenditure by almost 500 calories/day. Remember that one of the key assumptions of the CRaP theory is that in response to caloric change, TEE does not change. This is clearly NOT TRUE.

Instead of a simple calories in, calories out model where fat is deposited according to an excessive intake of calories, it appears that the body responds to excess calories by trying to burn them off!

Now let’s see what happens as the weight is returned to normal. Here, things start to get really interesting. As weight returns to normal, TEE returns to baseline. As we move into 10% and 20% weight loss, the body reduces TEE by about 300 or 400 calories per day.

So, as we begin to lose weight, the body responds to the weight loss by reducing TEE. This slows weight loss, and encourages weight regain despite full compliance with the diet. In other words, an increase in Calories In causes an increase in Calories Out. A decrease of Calories In causes a decrease in Calories Out. This is the body’s normal response. Weight loss will plateau, but not because you weren’t following the diet. Because that is the expected physiological response. It happens to everybody!

If you were trying to lose weight by eating less (Caloric Reduction as Primary), this is where you go, “WTF?!! OMG, That sucks! Where’s my frowny face emoji?”

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Our body acts much more like a thermostat. That is, the body seems to have a certain Body Set Weight (BSW). Any attempts to increase above this BSW will result in our body trying to return to its original weight by increasing TEE (increasing metabolism to burn off the excess calories).

Any attempts to decrease below this BSW will result in our body trying to return to its original weight by decreasing TEE (decreasing metabolism to regain lost calories). No wonder it is so hard to keep the weight off! As we slow our metabolism, we must further and further reduce our caloric intake to maintain weight loss.

Here’s the misguided dietary technique of portion control or Caloric Restriction as Primary. We reduce our portion size but keep meal timing and composition the same. We reduce our calorie consumption from 2000 cal/day to 1,600 cal/day. Our weight may reduce, but then the body would respond by reducing TEE to about 1,600 cal/day. We might feel cold, tired, miserable, and hungry. If you have ever been on a diet — you probably know how that feels.

The worst part of it is that we don’t lose any further weight because we are eating less and burning less. Any slip in the diet, even to the previous normal 2,000 cal/day will result in weight regain. Discouragement sets in. We get tired of feeling so lousy so we go back to our regular diet. All the weight comes racing back with a little extra for good measure.

We feel that we have failed ourselves. We think that it is our fault. Our doctors, dietitians, and other medical professionals silently criticize us for ‘failing’. Others silently believe we have no ‘willpower’, and offer meaningless platitudes. Sound familiar? Yeah, I thought so.

But in truth, the failing was not ours. The portion control diet is virtually guaranteed to fail. It has been proven over and over in the last 100 years. The only reason we think that it works is because everybody — the doctors, the dietitians, the ‘scientists’, the media — have convinced us that it is all about calories. No, the failing is with our nutritional authorities.

Clearly, something is causing us to gain weight, but calories sure don’t look like the problem or the solution here. What is that problem? What is the etiology of obesity? What causes fat gain?

Better Humans

Better Humans is a collection of the world's most…

Dr. Jason Fung

Written by

Nephrologist. Special interest in type 2 diabetes reversal and intermittent fasting. Founder of Intensive Dietary Management Program.

Better Humans

Better Humans is a collection of the world's most trustworthy writing on human potential and self improvement by coaches, academics, and aggressive self-experimenters. Articles are based on deep personal experience, science, and research. No fluff, book reports, or listicles.

Dr. Jason Fung

Written by

Nephrologist. Special interest in type 2 diabetes reversal and intermittent fasting. Founder of Intensive Dietary Management Program.

Better Humans

Better Humans is a collection of the world's most trustworthy writing on human potential and self improvement by coaches, academics, and aggressive self-experimenters. Articles are based on deep personal experience, science, and research. No fluff, book reports, or listicles.

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