In 1984, I was a Freshman in high school and much more interested in making the soccer team, getting kicked out of my honors classes and that girl sitting over there, than I was into the medical literature of the day. Which would explain why I missed an article by Rudolph Leibel and Jules Hirsch examining why we can't keep lost weight from coming back.

This was pre-Oprah, if such a thing can be imagined, so it seems that the public mostly missed this article as well. It appeared in the February issue of Metabolism and was titled "Diminished Energy Requirements in Reduced-Obese Patients." 

What they wanted to know was this: Are heavy people who say they don't eat much totally full of crap? Well, they didn't quite phrase it that way, but they investigated the apparent phenomena of weight plateaux and regain patterns by asking: Do people actually need less food than expected after they've lost weight? Do their bodies somehow compensate and simply survive on less food? This is what many patients claim. But is it true?

It turns out, it is, quite clearly, true.

As the authors mention themselves, their methods were decidedly low-tech. This was a retrospective analysis of data gathered on the most successful participants of previous liquid diet trials at their institution. In the weight loss program, they checked volunteers into a  hospital ward and prepared all of their meals with analyzed calorie counts, carefully measured ingredients and weighed all amounts eaten and left-over. 

Letting the study subjects self-select food quantity and weighing them daily, Drs. Leibel and Hirsch calculated how many calories lean and obese subjects needed to maintain their baseline weight.

The first surprise: "The obese and control subjects required comparable caloric intakes."

Then, they analyzed what happened after the use of an aggressive meal replacement liquid diet of 600 calories/day which produced a very large weight loss in the treatment group. They then stabilized the participants at the new weight (50 kg less!) and calculated how much food was needed to keep them steady at the lower weight.

The second surprise: "Following weight loss, the reduced-obese subjects required only 1021 +/- 32 kcal/m*m/day, a 28% decrease compared to their obese state and a 24% decrease relative to the control patients."

The third surprise: "The mean individual energy requirement of the reduced-obese subjects (2171 kcal/day) was less than that for the control subjects (2280 kcal/day) despite the fact that they still weighed 60% more than the controls." In the understated tone typical of good science, the authors concluded, "This finding has implications with regard to the pathophysiology and treatment of obesity in humans."

I'll say it has implications. Obese and lean people eat the same amount? Obese people need 28% fewer calories after weight loss? Obese people have to eat less than people who are much lighter than them, just to keep weight off? Those facts have enormous implications for how we think about weight loss and they don't seem to be common knowledge. In fact, I hear most physician colleagues give the exact opposite opinion to their patients: that metabolisms don't vary. When did a doctor or a trainer or a dietitian ever tell a client that they are going to lose a ton of weight, still be quite heavy and have to eat less than a skinny person, forever, to maintain that weight loss?

These conclusions regarding the needed caloric intake for those who have successfully lost weight are reinforced by data from the National Weight Control Registry, which is run by Rena Wing, from Brown with James Hill, Holly Wyatt and colleagues at the University of Colorado School of Medicine. They created the registry after realizing that so few people are successful with long term weight loss, it might be fruitful to just ask the exceptions, those that actually make it long term, what they do that seems to be working.

In order to be included in the ongoing surveys and studies, participants must have lost at least 30 pounds and kept it off for a year. The average participant in the group has actually lost 60 pounds and kept it off for five years. With regard to calories, the women report eating 1300 calories per day, the men just 1600. This corroborates the findings from Leibel and Hirsch: people who have lost weight need to eat much less than the naturally lean, if they are to keep the weight off.

Leibel and Hirsch built upon their previous findings in 1995 with a different group of lean and obese subjects. In this study, Changes in Energy Expenditure Resulting from Altered Body Weight, they looked at how the body reacts to weight gain, in addition to weight loss. By systematically overfeeding or underfeeding the volunteers, they were able to show that all of the study subjects altered energy expenditure in such a manner as to bring the body back to the starting weight. That is to say, when they caused the subjects to gain 10% of their body weight, the metabolism sped up in an attempt to burn off the excess.

When they reduced the subjects by 10%, the metabolism slowed down to compensate. The increase that occurred after weight gain was more than expected for the increase in body mass. The decrease in metabolism was more than expected from the loss of body mass. The body was over-compensating to fight back to normal. These same researchers went on to show, in 2008, "this disproportionate decline in [energy expenditure] persists after dynamic weight loss has ended...regardless of whether that reduced weight has been maintained for weeks or years."

Not every study that has looked for the phenomenon of slow metabolism after weight loss has agreed with the Leibel/Hirsch findings. Drs. Wyatt and Hill, who's registry suggests such very low maintenance calorie requirements when subjects self-report, went on to try to validate this more scientifically. They reported in an American Journal of Clinical Nutrition article in 1999, that the subjects they had actually brought in for metabolic testing were indistinguishable from a control group. So this suggests That there is likely significant under-reporting of calories in the registry. 

However, when it comes to this sort of proposition (might some individual's have slow metabolism? And does it change as we lose weight?), we do not have to prove the phenomenon to be universal, we need only prove that it is possible. If it occurs in some, we need to change our thinking, which previously had denied the possibility that individuals vary with regard to core metabolic parameters. Since metabolic studies demonstrate that our bodies fight our weight loss efforts, it's critical that the professionals counseling clients recognize the difficulties facing a person trying for long term changes in body shape and health.

Patients have generally been misguided by their physicians. Because there is no specific lab tests for metabolism (short of the very expensive, complicated procedures in the academic studies) physicians are generally unaware of the variability of these factors. The patients are usually told that there is no biological reason that they can't lose weight. The patients have been taught that obesity is the result of gluttony and sloth and that their inability to get lighter is due to a lack of willpower.

The science simply doesn’t back this up (in fact, the willpower nucleus in the brain has yet to be found). But patients have been so trained to blame themselves and told so often that their metabolism is normal (by physicians) that they can spend a lifetime trying to achieve something that may be, for all practical purposes, impossible: maintain meaningful weight loss.


Leibel and Hirsch. "Diminished Energy Requirements in Reduced-Obese Patients." Metabolism, Vol. 33 No. 2 (Feb), 1984.

Rosenbaum, Hirsch, Gallagher, Leibel. "Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight." Am J Clin Nutr 2008; 88:906-12.

Leibel et. al. "Changes in Energy Expenditure Resulting from Altered Body Weight." NEJM, Vol. 332 No. 10 (March 9) 1995.

Wyatt, HR, et. al. "Resting energy expenditure in reduced-obese subjects in the National Weight Control Registry." Am J Clin Nutr 1999; 69:1189-1193.