Metabolic rate makes keeping weight off harder for some

DEAR DOCTOR K: I heard about a recent study that explained why the "Biggest Losers" had trouble keeping the weight off. Can you explain?

DEAR READER: You're likely referring to a study done at the National Institutes of Health (NIH). As many readers will recall, NBC television put on a competition reality show for several years, beginning in late 2004. Extremely overweight people competed to see who could lose the most weight, through diet and exercise, over 30 weeks.

In summary, the competitors did a remarkable job of losing weight. But then they slowly gained most of it back. Sound familiar? The study suggests that one reason they had trouble keeping the weight off involves their resting metabolic rate.

What is resting metabolic rate, and how does it relate to body weight? Our weight is greatly affected by the balance between the calories we consume in food and the calories our body burns. Most people know that. What is not as well known is that the efficiency with which our body burns calories can be quite different, varying from one person to the next.

You probably know people who seem to eat like a horse but are not overweight, and others who don't eat much and do exercise, yet are overweight. The difference is that the first group burns calories more readily. Their resting metabolic rate is higher.

What is even less well known is that a person's resting metabolic rate changes over time. For example, our brain sends signals that lower our metabolic rate when we lose weight. Why would that be? It's because our ancestors tens of thousands of years ago were often hungry, often going days without food. The brain could slow the potentially dangerous loss of weight by telling the body to burn fewer calories.

Our genes today are not very different from those of our ancestors long ago. But in the developed nations, we're almost all well-fed. More of us are overweight than underweight. The genes that protected our ancestors actually cause problems for us.

The recent study followed contestants in the "Biggest Loser" competition six years after the competition ended. Their average weight before the competition was 328 pounds. After the 30-week competition, it was 200 pounds. As expected, their metabolic rate had dropped as they lost weight.

The surprise: Six years later, their average weight was 290 pounds -- but their metabolic rate had not gone back up as they regained those 90 pounds. As a result, they still were not burning many calories, making it harder not to regain weight.

The study offers one explanation for why weight loss during dieting usually cannot be maintained. As research improves our understanding of what controls the metabolic rate, we may develop tools for helping achieve and maintain a healthy weight.