Your body fat conserves your energy, keeps you warm, cushions your organs and allows the body to maintain the basic functions that keep you alive. Your ideal body fat percentage will be different from that of other people. How much each person has depends on some things that can't be changed including age, bone structure, biological sex and genes, in addition to things we can change, such as whether we lead an active or sedentary lifestyle.
Too much body fat is associated with chronic disease such as type 2 diabetes, cardiovascular disease and some cancers. But the pendulum can swing too far in the other direction. You can have too little body fat, which poses a different set of health issues.
A body needs to have a certain percentage of fat in order for it to be able to function: Women need about 13 percent body fat and men about 3 percent. This is your essential body fat and doesn't include any fat stores. In addition to essential body fat, a body also needs storage fat. On average, 15 percent of a woman's body weight should reflect her storage fat, and that number is about 12 percent for men.
When body fat drops lower than 14 percent for women and 8 percent for men, health risks increase, including everything from reproductive dysfunction (such as amenorrhea in women), dehydration, starvation, loss of muscle tissue and premature osteoporosis, in addition to complications such as organ and nerve damage [source: UPDR].