Mayo Clinic Health Library

Question

Slow metabolism: Is it to blame for weight gain?

Is it possible to be overweight because of a slow metabolism?

Updated: 08-23-2011

Answer

Probably not. There is such a thing as a slow metabolism. But slow metabolism is rare, and it's usually not what's behind being overweight or obese — that's usually a matter of diet and exercise.

Metabolism is the process by which your body converts what you eat and drink into energy. Even when you're at rest, your body needs energy for functions such as breathing, circulating blood and repairing cells. The number of calories your body uses for these basic functions is known as your basal metabolic rate (BMR).

Several factors determine your basal metabolic rate:

  • Your body size and composition. If you weigh more or have more muscle mass, you will burn more calories, even at rest. So overweight people are more likely to have a faster metabolic rate — not a slower one.
  • Your sex. If you're a man, you probably have less body fat and more muscle mass than does a woman of the same age, so you burn more calories.
  • Your age. As you get older, your muscle mass decreases, which slows down the rate at which you burn calories.

Rather than slow metabolism, factors more likely to contribute to weight gain include:

  • Eating too many calories
  • Getting too little exercise
  • Genetics and family history
  • Certain medications
  • Unhealthy habits, such as skipping breakfast or not getting enough sleep

If you're concerned about slow metabolism and your weight, talk to your doctor about healthy changes you can make. And if you still think you have slow metabolism, your doctor can check your metabolism or check for rare conditions that can cause problems with metabolism, such as hypothyroidism and Cushing's syndrome.