One of the primary motivators for folks beginning an exercise program is a desire to reduce unwanted body fat. But exercise alone may not be enough to significantly tap into adipose tissue, the fat pads beneath your skin where your body stores extra calories. Understanding more about how your body stores and uses energy will help you choose exercises and lifestyle strategies that are effective for fat metabolism.
Essential vs. Storage Fat
While we tend to view fat as the enemy, some fat is desirable and even essential to healthy body function. Sports coach Brian Mac explains that essential fat is stored in the bone marrow, vital organs, muscles and nervous system to be used for normal physiological processes. Women have an extra 9 percent for functions related to reproductive health. In healthy adults, storage fat that accumulates in adipose tissue accounts for about 12 percent of men's body weight, and 15 percent of women's. Storage fat is reduced when energy expenditure exceeds intake. Increasing physical activity and reducing caloric intake is a two-pronged strategy that will accelerate fat loss.
Fat vs. Carbohydrate Recruitment
According to University of California at Davis researchers Ann Albright and Judith Stem, excess calories, whether ingested as carbohydrates, fat or protein can all be converted to triglycerides and stored in adipose tissue. Your cells draw on both fats and carbohydrates throughout the day for everyday activities. When activity intensifies, as during exercise, your recruitment of fat from adipose tissue is dependent on the presence of oxygen and the availability of glucose for energy production.
Exercise and Adipose Tissue
Because fat is an oxidative fuel that is broken down slowly when oxygen supplies are adequate, very high intensity exercises like heavy weight lifting and sprinting rely primarily on glucose for fuel. During lower-intensity long-duration activities like jogging or cycling where oxygen is in ample supply, adipose tissue is increasingly drawn upon for energy as glucose stores become depleted. Exercise regimens like high intensity interval training, or HIIT, use a combination of fat and glucose for fuel, and may burn more total calories from fat during a single session than low intensity endurance exercise.
Intensity and Fat Metabolism
While you do not draw directly on fat stores to fuel heavy resistance training exercise, it is still an important ingredient in the recipe for weight loss. That is because resistance training builds muscle, and muscle in turn revs up your metabolism, meaning you burn more calories throughout the day. Your body also recruits fat in the post-exercise recovery phase. In the final analysis, the amount of energy you expend at the gym can be just as important as the type of exercise you do. Increasing your muscle mass, burning more calories and decreasing your daily caloric consumption is the most effective strategy for decreasing unwanted body fat.