What nutrient is converted into fat when it is consumed in excess of the body's needs?

Any excess calories a person takes in from carbohydrates, fats or proteins are converted and stored as body fat, according to the Cleveland Clinic. Some body fat is necessary, according to Nutrition.gov, but excess body fat increases the risk of diabetes and heart disease.

According to Iowa State University, most men should have between 10 and 20 percent body fat and women should have between 20 and 30 percent body fat to maintain good health. A healthy amount of fat protects vital organs, allows absorption of fat-soluble vitamins and insulates the body. To lose weight and body fat, Nutrition.gov recommends that a person eats fewer calories than he burns each day.