It turns out that losing weight and keeping it off is not only a question of willpower. New research published today in the New England Journal of Medicine investigated the issue by limiting 50 obese or overweight adult men and women to a very low-calorie liquid diet for 10 weeks. After reintroduction of regular foods, the participants were followed for an additional year to determine whether they could keep the excess weight off, and how their physiology changed. Importantly, levels of several hormones involved in the regulation of body weight and appetite were assayed both before and after weight loss, and again after one year of follow up. These hormones, it turns out, may explain why it's so difficult to maintain a loss of weight.
After ten weeks, levels of hormones that inhibit eating had significantly decreased, while levels of hormones that stimulate hunger and eating had significantly increased. Most importantly, the changes in hormone levels and hunger after the 10-week dieting period were essentially unchanged one year later. At the end of the one-year follow up, the participants had indeed regained some of the weight they had initially lost.
The authors concluded that the circulating mediators [the hormones] of appetite that encourage weight regain after diet-induced weight loss do not revert to baseline values within 12 months after the initial weight reduction.
The take-home message of this study, says ACSH's Dr. Ruth Kava, is that maintaining weight loss long-term means fighting against the physiological mechanisms that prompt weight regain. Therefore, she continues, these results should encourage us to avoid weight gain in the first place.