Your body fat percentage is a measurement comparing your fat stores to your overall body weight. People whose percentages are too high — over 24 percent for men and over 31 percent for women — are classified as obese, according to the American Council on Exercise. They are at higher risk for cardiovascular disease, diabetes and some cancers. But dangers also exist for people whose body fat percentage drops too low.
It’s a common myth that all body fat is bad; your body needs some fat to function properly. Fat helps insulate your body and serves as an energy source. After roughly 20 minutes of exercise, your body no longer can draw energy from carbohydrates you’ve eaten, so it turns to fat stores to continue contracting your muscles.
Low body fat levels can lead to incomplete recoveries after workouts; depleted glycogen stores; nutritional deficiencies that lead to further problems, such as bone loss; decreased performance; chronic fatigue; increased risk of infection; and injury, according to “The Complete Book of Sports Nutrition: A Practical Guide to Eating for Sport.” If you cycle between a low and high body fat percentage, over time this may result in a decrease in lean body mass and increase of fat. If your low body fat percentage results from eating disorders, you might experience the risks that accompany those conditions as well.
If you’re female, a low body fat percentage can cause a hormonal imbalance. The hypothalamus in your brain recognizes that your body fat percentage has dropped too low. It decreases production of a hormone that affects the pituitary gland, which in turn reduces the production of hormones that affect ovaries. Then your ovaries decrease production of estrogen and progesterone, so your menstrual cycle might stop. This can lead to infertility. Low body fat percentages also have an effect on men’s hormones. Testosterone levels decrease, which might make it more difficult to create lean muscle. It also results in decreased production of sperm and loss of sexual desire.
Individual factors affect how low your body fat percentage must fall before you begin to experience problems. For females, body fat percentages below 15 to 20 percent are considered dangerous, according to “The Complete Guide to Sports Nutrition.” For men, body fat percentages below 5 percent are risky.