Can People Actually Have Slow Metabolism?

Your body uses energy constantly, even while you sleep, and the energy required to keep your body alive is called your basal metabolic rate, or BMR. Many factors contribute to your BMR, including your age, sex, activity level, muscle mass, hormones, nutritional status and, to a lesser extent, genetics. Even if you are genetically predisposed to a slow metabolism, you can increase your metabolic rate through an active lifestyle and healthful diet.

Metabolic Rate Basics

The activity of your heart, brain, liver and kidneys account for roughly 60 percent to 70 percent of your resting energy use, report Dr. Fahad Javed and colleagues in an April 2010 article in the "American Journal of Clinical Nutrition." These vital organs utilize most of the energy when your body is at rest because they remain continuously active. Although 40 percent to 50 percent of your normal body weight is muscle, these tissues account for only 20 percent to 30 percent of your resting energy use. Fat, or adipose tissue, uses a low amount of energy. Being overweight or obese, however, can significantly increase your BMR.

Age and Sex

Your age and sex are important contributing factors to your BMR. Periods of rapid growth, such as infancy, puberty and pregnancy, are associated with a high BMR. In contrast, loss of lean body mass associated with aging reduces your BMR. Your metabolic rate is likely to be lower if you are woman because testosterone, the male sex hormone, boosts BMR. If you are an older man, your BMR might slow as your testosterone level decreases.

Thyroid Hormones

Thyroid problems are commonly blamed for a slow metabolism. Thyroid hormones influence the activity of virtually every tissue in your body, thereby affecting your metabolic rate. An underactive thyroid, or hypothyroidism, reduces your BMR and might cause weight gain. Other symptoms can include feeling cold when others are comfortable, persistent tiredness and lack of energy, poor concentration and forgetfulness, constipation, facial puffiness, dry skin and brittle hair. If you have several of these symptoms, talk with your doctor about having your thyroid hormones checked. Although hypothyroidism slows BMR, it is important to recognize that thyroid problems are not the cause of most weight gain and slow metabolism.

Physical Activity

Your activity level affects your BMR, which declines with a sedentary lifestyle and increases with regular physical activity. When you exercise regularly, you not only burn calories associated with the physical activity but also increase the number of calories burned at rest --- an added bonus that's hard to beat, metabolically speaking.

Dieting

A very low-calorie diet is likely to slow your metabolism. Your body detects markedly low caloric intake and responds by going into "starvation" mode, slowing your metabolic rate to conserve energy. Although you are likely to lose weight on very low-calorie diet, you will probably gain it back quickly once you return to a regular eating pattern because of your reduced metabolic rate. If you want to lose weight, talk with your doctor about setting your target caloric intake, which should be low enough to prompt weight loss but high enough to make metabolic slowing unlikely.