It’s true that losing weight can reduce the number of calories you burn, but I wouldn’t dwell on it. It’s tough to predict just how much your metabolism will drag and how long the slowdown will persist; the scientific research on the metabolic effects of weight loss is a little all over the place. Some studies have found that overweight or obese people who lose weight do suffer lasting metabolic damage that makes it hard to keep the pounds off later. But other research has found that those same groups can drop pounds with no long-term penalty at all. Don’t forget: Metabolism is partly genetic. That means that even if you and your best friend shed the same amount of weight, your bodies could respond differently.
Interestingly, some experts now believe that the speed at which you lose weight may be an important factor in what happens to your basal metabolic rate (that is, the calorie burn at rest). There’s evidence that people who lose weight quickly through intense calorie restriction see a significant metabolic slowdown. That’s because when you create a dramatic calorie deficit—by slashing calorie intake big time or going crazy with exercise—your body fights back and tries to hold on to energy by reducing the number of calories you burn; this is often referred to as “starvation mode."
Until the research is more definitive, the best piece of advice I can give (and you’ve probably heard it before) is to slim down slowly, whether you have five pounds to lose or 50. Metabolism aside, a slow and steady weight-loss plan is a more sustainable lifestyle change than a crash diet. Most experts recommend losing at a rate of one pound per week, by creating a calorie deficit of roughly 500 calories a day (a registered dietitian can help you craft a more tailored nutrition plan). One more bit of advice: Make time for strength training. Increasing your muscle mass will help you burn more calories at rest.
Health’s medical editor, Roshini Rajapaksa, MD, is assistant professor of medicine at the NYU School of Medicine.