How Caloric Reduction Wrecks your Metabolism – Calories Part VI

By Jason Fung, MD

Click here for Calories part I, part IIIpart IV, and part V. In previous posts, we have reviewed how eating less does not result in permanent weight loss. In the classic studies of caloric reduction the result was a significantly lowered metabolic rate or Total Energy Expenditure (TEE).

Let’s now fast forward to the modern era, and look at this study published in the prestigious New England Journal of Medicine.
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. Great! This is exactly what we want to know as well, because we don’t really like the answers the classic studies gave.


Well, what happened? The results graph to the left shows the changes in TEE with the different experimental groups. Let’s start by looking at the 10% weight gain group. In response to the weight gain 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 it 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, thereby slowing down further weight loss, and encouraging weight regain. This is all done without changing the dietary composition of the food, since all participants were taking in the same liquid 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, of course, tends to minimize the effect of the increase or decrease of caloric intake.

If you were trying to lose weight by eating less (Caloric Reduction as Primary), this is where you go OMG, That sucks!”

Rather than the simple balancing scale of calories in calories out, it appears that 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 the body 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 the body 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.

Hmm. This actually makes a lot of sense. In fact, this is assumption #4 of the CRaP theory. We assume that fat gain or loss is unregulated by the body. We assume that as we eat more we keep gaining weight and as we eat less and we keep losing weight. But there is no system in the body that is unregulated like that! Everything is under hormonal control. It makes far more sense that the body has a system to control body weight. (Actually it has multiple systems).

Let’s put this into a dietary context. Suppose we are at a stable weight. We eat 2000 calories and burn 2000 calories every day. We keep our diet constant but just increase or decrease the amount. Suppose we super-size our portions but otherwise keep our diets constant.

Weight may increase but the body’s response would be to increase daily Total Energy Expenditure – body temperature may increase, energy and sense of well being may increase. We may eat 2,500 cal/day but the body has now increased TEE to 2,500 cal/day. No further weight will be gained and the body will attempt to reduce our weight back to the original. In the meantime, we feel great.

Let’s do the opposite – the misguided dietary technique of portion control. 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. In fact, this is exactly what happened in the semi starvation experiments done by Dr. Ancel Keys as well as those at the Carnegie Institution in 1917.

We feel we have failed ourselves. We think that it is our fault. Our doctors, dieticians, and other medical professionals silently criticize us for ‘failing’. Others silently think 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 dieticians, the ‘scientists’, the media – has convinced us that it is all about calories.
Clearly something is causing us to gain weight, but calories sure don’t look like the problem here. What is that problem?

Continue to Calories Part VII here
Begin with Calories I
Click here to watch the entire lecture: The Aetiology of Obesity 1/6 – A New Hope

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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