Why Metabolism Slows Down
Muscle determines how fast the body’s engine runs and how many calories the body burns over the course of a day. Muscle falls into the “use it or lose it” category—if your muscles are not active, they will shrink. Since we tend to get less active as we get older, our muscles become smaller, and, as a result, our metabolism and calorie burning slow down. Research has shown that the impact of age-related changes in hormones is much smaller than the impact of muscle loss from lack of use.
Even if your weight stays the same as you get older, the amount of fat and muscle on your body will change. This is not the result of aging per se. Because adults become less active as they get older, they’re likely to have more body fat and less lean tissue than in their younger years. A study published in Nutrition found a clear link between activity and body composition. People who were more physically active in their daily lives and through regular exercise had more muscle. The study also found that weight and body fat increased with age.
Any weight gain during adulthood is likely to be body fat because most adults are not active enough to build muscle. Some studies suggest that by age 55, the average person in the United States has added over 37 pounds of fat during his or her adult years!
Here’s the good news. According to the American College of Sports Medicine, as part of a regular physical activity routine, muscle-building strength training can slow down muscle loss and help keep metabolism revved up.