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Why don’t Diets Work

Low-calorie diets are the accepted means of weight loss by most medical professionals, despite the fact that they have repeatedly been shown not to work for long-term weight reduction and maintenance. But is this traditional approach at least useful for short-term or “emergency” situations (like that 25th high school reunion)? Well, many would argue that a couple of months on Nutrisystem or Weight Watchers or the fad diet du jour can be an effective means of reducing, if followed by a maintenance program of eating a “normal intake”. Well, as it turns out, even a brief period of significantly reduced intake will cause the body to dramatically adjust its level of “energetic efficiency”-the rate at which calories are partitioned toward energy versus fat storage, making this not only a useless way to alter one’s physique, but a detrimental one, as well.

Let’s look at some scientific research on the subject. Here’s what happened when a group of rats decided to “lose a few” for bikini season. In a cleverly designed experiment (“Adaptive Changes in Energy Expenditure during Refeeding following Low-Calorie Intake”, Am J Clin Nutr 1990; 52:415-20) by long-time obesity researchers Dulloo and Girardier, half of a group of young rats were put on a diet, while the others were allowed to eat whatever they wanted (the “ad libitum” group). The dieters were fed exactly 50% of what the ad lib rats ate spontaneously, for a period of 30 days. At the end of that time, the dieting group was then matched to a third group of rats by both weight and body composition. For the next 25 days, the previously food-restricted rats were fed exactly what these similar-sized, non-dieted rats chose to eat naturally. If there was no adaptive mechanism, the two groups of animals would be expected to dispose of the calories in a similar fashion, but in fact, that was not at all what happened.

Since they were young rats, they all gained weight during the 25 days of pair-feeding, but the raw gain and relative proportions of fat and lean tissue were vastly different. The dieted rats gained the same amount of lean tissue, about 25 grams, but more than twice the fat of their free-eating counterparts-35 grams versus 15! Thus, they not only gained a whole lot more weight, but a much greater percentage of it as fat (58% vs. 36%), while eating the same number of calories as rats who were initially similar in size and body composition. The only explanation for this is that the 30-day low-calorie period devastated the fat-burning machinery of the diet group, so that they not only recouped lost weight but turned into fat-storing machines.

Thus, when dieters return to “normal” eating, where normal is the amount eaten by a person of similar size and body composition to their new, thinner physique, they will lay down fat like nobody’s business. But if you’ve ever been on a low-calorie diet, you don’t need me to tell you that-you’ve experienced it yourself. You’ve felt the anguish of watching everything you worked, sweated, and starved so hard to take off, jump right back on your bones as though they were magnetic. There’s probably no worse feeling than stepping on that scale every day, when you’re trying so hard to keep the weight off, and seeing those numbers creep-creep-creeping back up.

But does it have to be this way? No, not if you have the courage to ignore what “everyone” says is the cure for obesity and instead avoid low-calorie dieting as a means of reducing. As this study shows, diet and exercise programs designed to create a caloric deficit are not a useful long-term solution to excess weight, and in fact, make the problem that much worse. Instead, we must develop an understanding of the physiological causes of obesity and work on treating them, rather than simply applying a painful and often expensive bandage over the problem.