Hard to Lose Weight, Harder to Keep It Off
A remarkable new study explains why.
By Mark Yarchoan
For years, studies have confirmed what is obvious to anybody who has tried to lose weight: weight loss is challenging, and keeping lost weight off is even harder. In 2005, a landmark study published in the Journal of the American Medical Association comparing a number of popular diets – Atkins (carbohydrate restriction), Zone (macronutrient balance), Weight Watchers (calorie restriction), and Ornish (fat restriction) – found that all of the most popular diets are similarly ineffective. At the end of one year, people who had attempted to diet using any of these strategies lost an average of only about five pounds. Other studies have found that more than 90% of people who lose a lot of weight eventually gain the weight back.
These studies should not be considered a reason or excuse to avoid dieting. Even small amounts of weight loss and changes in lifestyle can have truly dramatic effects on health, including improved blood pressure and glucose control for people with diabetes. However, it is important to have realistic expectations about weight loss, because weight loss involves fighting a set of embedded forces in the body that are designed to prevent weight change. Although the conscious brain may be saying, "it's time to lose weight", a complex interplay of weight-related hormones may be saying something different.
The average American eats over 70 million calories in a lifetime, plus or minus a couple of million calories. Yet incredibly, for most people, body weight is kept within a relatively narrow range. Over the course of a decade, food intake and energy output is typically matched within 0.17%. This means that for almost everyone of any kind of build or weight, calories in and calories burnt are kept virtually equal. Working behind the scenes is a complex interplay of hormones and neuronal circuits that control hunger and metabolism so that both sides of this energy equation remain equal. This Learning Curve attempts to explain what these hormones are, how they work, and why their existence makes weight loss so challenging.
Leptin: A Long-Term Regulator of Fat
Originally discovered in 1994 by Dr. Jeffrey M. Friedman at the Rockefeller University, leptin is thought to be one of the most important regulators of weight. Children born with a rare genetic deficiency in leptin become morbidly obese at a young age, and their weight can be mostly normalized when leptin is administered to them. Leptin is secreted from fat cells and acts somewhat like a thermostat for weight. When a person gains weight, more leptin is produced, causing a decrease in appetite and an increase in energy metabolism. When weight is lost, the opposite happens.
It's easy to understand why leptin makes successful dieting so difficult. When a person starts dieting, leptin levels fall dramatically even with modest weight loss. The fall in leptin is sensed by the brain, and the dieter begins to experience increased appetite. In addition, a fall in leptin levels makes high-calorie food taste better, and eating begins to feel more rewarding. As a result of low leptin levels, dieters may actually crave high calorie foods like potato chips. In addition to promoting increased calorie intake, the fall in leptin also decreases metabolism by making the body more efficient. Fewer calories are burned in muscle and other tissues at rest and while exercising. These converging effects of a fall in leptin – increased appetite and decreased energy metabolism – may explain why so many dieters regain weight that they worked so hard to lose.
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