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Beware of DietWhat if counting calories makes you fatter in the long run?

By Sydney Spiesel
Posted Wednesday, July 4, 2007, at 8:25 AM ET
Woman standing on scales. Click image to expand.

Do diets work? The great majority of doctors think so. Experience tells us to expect an enormous failure rate, yet most of us continue to hold out hope that the diets we prescribe will result in lost weight or other health benefits. Why do we keep believing? First of all, because dieting really ought to work—here's the standard explanation. Calories are energy. The body stores excess energy (beyond what we need for motion and the chemical processes of life) in fat. If we cut down our caloric intake (or increase our energy output) below the amount of energy the body uses, our weight will fall.

This should happen in a predictable and mechanistic way, just as we were taught in pre-med science courses. Thus, dieting failure is supposed to reflect failure of adherence, which we've assumed to be the result of moral failure—lack of self-discipline and control. That probably explains why for years "obesity" wasn't recognized as a diagnosis by Medicare, Medicaid, and private insurers. But this approach hasn't worked well: Over the last 25 years, the obesity rate in the United States has jumped from 15 percent to about a third of the population, with another third deemed simply overweight. Insurers have come to understand that patients with untreated obesity develop more expensive medical problems in the future. Now they'll pay for dieting as a treatment—and we are forced to confront the question of what that's likely to accomplish.

There is considerable evidence that in the short term, calorie restriction generally leads to an average loss of about 5 percent to 10 percent of body weight. But the more important questions are these: Is the weight loss sustained over time? And does it have any long-term health benefits? These questions have recently been rigorously addressed in an exceptionally fine paper (PDF) by a group of researchers working with Traci Mann in UCLA's psychology department. These scientists systematically reviewed many studies of the long-term outcomes of dieting. And their results were hardly encouraging. Though the chemistry and physics of dieting seem straightforward, the biology and psychology may not be.

Mann and her colleagues examined three different kinds of research on the long-term outcome of dieting. First, they concentrated on the kind of studies that science likes best: random control trials. In these studies, patients interested in weight loss were randomly assigned to one of two groups. One group was given a calorie-restricted diet to follow; the other group was not. Many, many studies of this kind have been done over a relatively short period of time (often several months). But Mann and her group found only seven studies that followed their subjects over an extended period of more than two and a half years. And only a single "pure" long-term study randomly assigned participants to follow a diet or not, and simply measured weight change.

In this study, the experimental subjects were kept on their low-calorie diets for 18 months without other weight-loss interventions (like medications, exercise, or even pep talks) and their weight was measured again a year after the diet ended. A comparison of the dieting subjects with the control group (who were, instead, placed on a waiting list for a diet) showed some weight loss a year post-diet, but it was disappointingly small: an average decrease of 3.75 pounds. The other six long-term studies (which were muddier because they included other interventions besides diet) showed similarly unimpressive results: The average dieting weight loss maintained over extended time (between 2.5 and 10.5 years) was less than 2.5 pounds.

Mann and her colleagues also examined other kinds of studies on the long-term effects of dieting. In 14 studies that lacked control groups, but followed dieters for at least four years after a prescribed reduced-calorie diet, the average early weight loss after dieting was almost 31 pounds. But by the end of the follow-up period, on average the dieters gained back more than 24 of the pounds they had lost. In 10 studies in which nutritional scientists tracked the weight of people who put themselves on any diet of their choosing, the results were even worse. Of the 10 reports, only one described lasting weight loss, two showed no long-term effect, and the remaining seven studies found that dieting led to weight gain in the long run.

That result, of course, is particularly disturbing because it suggests that dieting is somehow monkeying with the body—perhaps by resetting the thermostat that controls how efficiently we utilize food—so as to make the struggle to lose weight all the more difficult. For instance, an excellent 2003 study of almost 15,000 preteens and teens followed for three years clearly showed that the kids who dieted gained more weight than the nondieters. This excess gain could not be explained by initial chunkiness, differences in caloric intake, or in the amount of energy contained in dietary fat.

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Sydney Spiesel is a pediatrician in Woodbridge, Conn., and clinical professor of pediatrics at Yale University's School of Medicine.
Photograph of a woman on a scale by Digital Vision.
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Remarks from the Fray:

Its a flawed belief to think that everyone can be physically fit, we don't all have the same motivations, lifestyles, nor do our bodies work the same way. Some people are more adept at burning calories naturally, some just can't seem to shed weight no matter what they do. I think its important that people recognize that fat people aren't necessarily gluttons. But I believe fat people need therapy - the same kind of therapy given to bulemics, anorexics, and other people suffering from eating disorders. More importantly, I think they need simple understanding from the people around them - not bigotry, condescension, or quick fixes - like diets.

--Eigenvector

(To reply, click here.)

Though I've read about the high failure rates of dieters, my anecdotal observations refute this. I know more people who have lost weight and kept it off, then who have yo-yoed or failed to lose weight. Though those who lost weight tended to be closer to a normal weight to begin with, and had at some time put on extra weight; while those who were heavier from the onset, seemed never to be able lose weight.

I simply don't believe that our increasingly heavier population is incapable of slimming down. There are more variables than just diet. If the person is heavy and rarely exercises, then exercise should be added to the equation. I'd also wonder if there are other factors, such as stress, that make it difficult to lose weight.

--pfire

(To reply, click here.)

If dieting doesn't work then the solution must be more dieting starting earlier in life and including every member of the family. If only someone authorized every meal eaten in a lifetime, people would weigh less. Or not.

But the important part is, someone has the authority to control what other people do. That has to produce improvement, right?! Even if some people die sooner because of yo-yoing weight. Okay, if dieting doesn't work because there are factors beyond diet, then exercise or diet and exercise have to work, right?

True, most people are not interested in exercising, as the article notes. And non-athletes who exercise are likely to suffer injuries, which sometimes allows them to stop before the increased risk of a heart attack can have an impact.

But some people can stick to a diet and undergo exercise without apparent harm. And that does produce a small but noticeable decrease in blood pressure. Approximately 1/10th of the amount needed to make them healthier.

The real antagonist for the controllers is that people have a natural weight and a natural amount of activity. Trying to change them is rarely advantageous.

I appreciate the honesty which has led to the current level of general understanding about "preventive medicine", also known as making statements that control what other people do. When the facts are recognized, I am optimistic that behavior will be more sensible. Not ordinary human behavior, but the actions of those who want to control them.

--Philidor

(To reply, click here.)

How many people who eat 3-4 satiating meals a day featuring whole grains, legumes, veggies, and olive oil with fruit snacks in between, and drink lots of water and tea; how many of these people are fat?

The diet study that I would like to see is to survey a large, random population on their current diet. How much do they eat in various food categories? What is their weight and health? Would it surprise anyone if eating more in the bad categories correlated to more weight and poor health?

There is absolutely nothing mysterious about dieting and health. Don't diet. Change your diet, permanently, and enjoy the benefits for the rest of your life. While we continue to feature refined flour, corn syrup, sugar and saturated fats in our restaurants and supermarkets, we will be a fat nation.

--ClavisRa

(To reply, click here.)

A diet isn't supposed to be a long-term fix. Examined objectively, the claim that something you did at age 20 will keep you thin at age 40 is pretty ridiculous. We don't expect our brains to retain material for twenty years - why would we expect it of our bodies?

The other reason that diets don't work is that many people don't know how to diet. The big benefit that participants in scientific studies (and famous pop stars) have over the average dieter is the advice and careful monitoring of industry professionals. Many people have a poor understanding of nutrition, or even what their body needs to function. I know that for many years I tried to diet without knowing exactly what a "diet" was. The result: even when I was slim, I was incredibly unhealthy.

Psychologically, I think diets are difficult because you start thinking you're holding back from something you truly deserve. For example, you're laying off brownies, but you wouldn't have to, if it weren't for your diet. The truth is, brownies are unnatural to begin with. In order to lose weight, people have to permanently change the way they think about food. And that's a tall order.

--AnikaG

(To reply, click here.)

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