The Astonishing Overeating Paradox – Calories Part X

Click here for Calories part I, part II, part III, part IV, part V, part VI, part VII, part VIII, and part IX.


Remember when you were in high school? You could eat and eat (pig out). Chips, pizza, soda pops. Later beer. And you’d never gain weight. You were as thin as a brief, forgotten dream. Slowly, it faded away. Lately, it seems that even looking the wrong way at a bagel puts on 2 pounds. What happened? What happens when we overeat?

If we look at the Caloric Reduction as Primary (CRaP) model again, we can see that this is a hypothesis that is easily tested. If eating too much causes obesity, then we should be able to overfeed subjects in an experimental setting and they should gain weight. This should be easy to do. Get some people. Make them eat too much. Watch them gain and gain weight. Bam. Case closed. Call the Nobel committee.

Luckily for us, these overfeeding experiments have already been done for us. The most famous of these studies was done by the endocrinologist Dr. Ethan Sims in the late 1960’s. He started off by recruiting college students to overeat. Turns out it wasn’t so easy to force these people to overeat. For those of you who have ever tried to feed a screaming baby who is refusing (because you thought he/she might starve to death) – you know what I’m talking about. Or maybe think about the last time you stuffed yourself at the local chinese buffet. Then try to imagine eating another 2 pork chops. Yeah, not so easy.

So Dr. Sims quickly abandoned that route and instead forced convicts at the Vermont State Prison to be in his experiment. Physical activities could also be strictly controlled. Initially convicts were fed 4000 calories/ day. They figured that was enough, but a funny thing happened. People started gaining weight initially but then the weight gain stabilized.

So, with a combination of scientific curiosity and loose ethical control (hello – informed consent?), some people were made to eat upwards of 10,000 calories/day. 10,000 calories per day! One man only gained 10 pounds with all that. However, most people did gain upwards of 20% of body weight. What happened to their energy expenditure? Metabolism, or Total Energy Expenditure (TEE) increased by 50%.

What is happening? Well, in response to increased calories, the body is increasing the energy it expends. Imagine that you have a fireplace in which you use 1 piece of wood every day. Now all of a sudden, you are getting 5 pieces of wood per day every day. Don’t you think you would want to start using a bit more wood? Of course. The body is also not that stupid that it would still use the same energy, so it increases TEE and we feel great. More energy. No coldness etc.

When the experiment ended, what surprised researchers the most was the rapidity with which body weight returned to normal. In fact, most of these people did not keep any of the weight they gained. So, here we see that overeating does NOT, in fact, lead to obesity. The body is more like a thermostat. While body weight may temporarily go above the set weight, it quickly reduces things back to normal.

Let’s look at a more recent experiment. This comes from the study:

Metabolic response to experimental overfeeding in lean and overweight healthy volunteers
Am J Clin Nutr Oct 1992;56(4): 641-55 Diaz EO

In this experiment, they took subjects and overfed them by 50% over a course of 6 weeks and then monitored for 6 weeks. The diet was 46% carbohydrate.



What happened to their weight? You can see the results in the graph to the right. Over the course of the overfeeding period fat mass did indeed increase. But what happened afterwards?

It is clear that the body weight quickly and automatically reverts back to its original body weight. It is almost as if the body has a set weight (BSW).

What happened to TEE? Using doubly labeled water, as well as indirect calorimetry, they tested what happened to TEE as subjects were overfed.


Experimental Overfeeding

Starting at a baseline average TEE of 13.2 MJ/day, they increased the TEE by 1.4 to 15.0. In other words, the body is ramping up energy expenditure to burn off this excess of calories coming in.

As the overfeeding period passed, TEE decreased back to 13.1 MJ/day. The weight came back down to normal and the TEE came back down to normal as well.

From the paper “we conclude that there was evidence that a physiological sensor was sensitive to the fact that body weight had been perturbed and was attempting to reset it”.

In other words, it appears that there is a body weight set point (BSW). An attempt was made to increase body weight by overeating, but the body fought against it and successfully managed to return to its original set weight.

But the important question is this:

What controls the body set weight? We need to know this to effectively work with our bodies to lose weight. We cannot simply restrict calories. We need to adjust this set weight.

So, it appears in fact, that overeating does not cause obesity at all. Therefore, attempts to lose weight by restriction of calories alone will not be effective, because too many calories was not the problem in the first place.


Continue to Calories part XI here

Begin with Calories I here

Click here to watch the entire lecture: The Aetiology of Obesity 1/6 – A New Hope

2017-09-02T11:54:32-04:0010 Comments

About the Author:

Dr. Fung is a Toronto based kidney specialist, having graduated from the University of Toronto and finishing his medical specialty at the University of California, Los Angeles in 2001. He is the author of the bestsellers ‘The Obesity Code’ and ‘The Complete Guide to Fasting’. He has pioneered the use of therapeutic fasting for weight loss and type 2 diabetes reversal in his IDM clinic.

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I don’t understand how you reach the conclusion “eating more does not cause weight gain” from the study above. ” Over the course of the overfeeding period fat mass did indeed increase.” So when people ate more, they got fatter. From the study: “All subjects [except for one] gained weight almost linearly during the overfeeding.”


These studies continuously increased calories until weight gain is achieved. This is only short term weight gain – it could not be sustained. Just like weight loss, it is only a short term, not a long term solution.


Are you arguing that if they continued overfeeding they would have eventually lost the weight that they had gained? If not, I’m not sure how this study supports your overall thesis or even your contention that “it could not be sustained.” My understanding from the earlier parts of this series was that your thesis was eating at reduced calories indefinitely is extremely difficult, if not impossible. However, it appears that you’re now arguing that even if you managed to eat at reduce calories indefinitely, you would eventually gain all your weight back, which I don’t think is supported by this,… Read more »


[…] פוסט זה מוגש כשירות לציבור. הזכויות על התוכן שייכות לכותב של הפוסט המקורי. את הפוסט המקורי ניתן למצוא בכתובת הזאת. […]


I think that the reason those people lost their weight again is because the study happened over the time of 6 weeks, which is reallyreally short. The body always wants to be in a bodyfat percentage in which it stayed for the last couple of years, trying to shift this bodyfat percentage up or down will take at least a year or 2. This is why all the people doing a contest prep and dieting down to 5% bodyfat gain alot of fat back eventhough they try to “leanbulk”, well the body wants to be in the same bodyfat level… Read more »


You are correct. People who get very fat or obese usually have food addiction or psychological overeating disorders, and by the time they get extremely heavy are typically eating 10-15,000 calories a day, like those on “my 600lb life”. And they are doing this for years, not six weeks. Yes, overeating is the one and only cause of obesity.

Dr Deepak S. Hiwale

Correct me if I’m wrong, but ideally a ‘paradox’ should mean people losing weight whilst overeating… Not the body regaining its set weight after cessation of overeating.


I gained my weight over the years consistently eating far more food than I had before. The overeating persisted and got even worse as time went on and so did the weight gain. It was not a short-term solution! If I had kept eating like that, I would have at least maintained, if not gained more. Now it may be that I didn’t gain as much as I “should” have, given my calorie intake, but I did gain. And maybe I haven’t lost as much as I should have, given my reduced calorie intake, but I have lost and maintained.… Read more »


[…] How strange is that? To take a look at the study CLICK HERE and a more detailed analysis HERE […]


[…] Jason Fung, a keen proponent of intermittent fasting for weight loss talks about one such overfeeding experiment in Vermont Prison. An interesting read. It’s amazing that some of those prisoners hardley […]

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