I've been dieting constantly on and off for years since I was a teenager, and have lost and gained the same 50 pounds more times than I can count. This last time I gained back even more. Have I ruined my metabolism?

The idea that people can "ruin" their metabolisms is a very disempowering notion. To put it simply, you can't. You may have some metabolic issues due to yo-yo dieting, and understanding how your personal metabolism works can only help you in your weight loss journey. Let me explain.

For the sake of example, let's say you lose 50 pounds just by dieting. Let's further assume that about half of the weight you lost is fat and half of it is muscle. (These percentages aren't exactly right, but they're good for the purpose of illustration.) You've now lost about 25 pounds of muscle and 25 pounds of fat. Now let's say that you go off the diet and regain that 50 pounds. This time, almost all of the regained weight is going to be fat, and virtually none of it is going to be muscle. So at the end of the day, you weigh the same as before, but your body composition is significantly different. You now have a significantly higher percentage of body fat.

Why does this matter? Simple. Most of your calories are "burned" by muscle tissue. Fat is basically metabolic "dead weight." When you lose a lot of muscle, you lose one of your biggest allies in the war against fat. This shift in body composition is one of the things people refer to when they talk about their metabolism being "ruined" by dieting. To bring your metabolic rate up, one of the best things you can do is regain some of that lost muscle by adding weight training to your routine.

The other thing that frequently happens with yo-yo dieting is that you train your fat storage enzymes to be more efficient. When you repeatedly starve yourself, those enzymes simply become better at their job, an evolutionary strategy meant to keep you alive during times of famine. But by exercising consistently, eating fewer calories than you burn, and by eating the right kind of calories, you can re-train the fat-releasing enzymes to come out of hiding.

And speaking of the right kind of calories ...

Most people in your situation have been trying to lose weight using a low-fat diet. Unfortunately, that's probably exactly what you should not be eating. Low-fat diets are typically high-carb diets, and high-carb diets virtually guarantee that your body will constantly produce high levels of insulin, also known as "the storage hormone." The body does not burn fat in the presence of high levels of insulin. The solution? A moderate-calorie diet that is higher in protein and good fats (such as olive oil) and lower in carbohydrates than your average low-fat diet.

The point is that there are specific positive actions you can take right now to work with almost any metabolic issue you may have as a result of your dieting history. Put these strategies into action right now, and maybe the next time you lose that 50 pounds will be the last time you have to do it.

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