The energy you need to run, lift weights or swim comes from a mixture of carbohydrates, fats and protein. The percentage contribution from each nutrient changes depending on the duration and the intensity of exercise. While exercising within the so-called fat-burning zone uses more body fat, exercising at a very high intensity burns significantly more calories. The bottom line is you must expend more calories than you eat to burn fat instead of storing fat while optimizing fat metabolism.
Exercise
Within the first 40 to 90 minutes of aerobic exercise, 40 percent of your fuel comes from the fatty acids released out of your fat cells, according to the authors of the book "Exercise Physiology, Energy, Nutrition & Human Performance." On the other hand, an all-out sprint interval workout for 30 minutes can burn almost as many calories as a 60-minute workout at low to moderate intensities. For instance, a 146-lb. adult running at 5 miles per hour will burn 528 calories in one hour. This same adult sprinting slightly faster than 8 ½ mph will burn 462 calories in 30 minutes. Exercising at very high intensities burns a significantly more amount of calories after the session and increases the concentration of fat burning enzymes to a greater degree compared to low to moderate intensity exercise. The end result is you will burn more calories from one bout of high-intensity training compared to one bout of moderate exercise, burning more fat and storing less fat.
Insulin Production
Insulin is a fat-storing hormone. Eating foods which contain carbohydrates stimulate insulin production by your pancreas. The more insulin your pancreas produces, the greater the potential of your body to store fat in your fat cells and in your muscle cells. If you have been eating plenty of refined foods or fast-digesting carbs like white rice, baked potatoes, table sugar, honey and fresh pineapple, your cells have been on insulin overload. Fatness and obesity are in part the end result of insulin at its best. Consider switching to slow-digesting carbohydrates including brown rice, all-bran cereals, cooked spaghetti, apples, oranges and skim milk. Including more lean protein in your diet also promotes the production of glucagon, a fat-burning hormone. The more glucagon your body produces instead of insulin, the more fat you burn and the less fat you store.
Stress and Cortisol
Cortisol is a hormone that helps mobilize the fat in your fat cells into fat which can be transported in your blood. This fat is used by your exercising muscles or can be stored deep within your abdominal cavity. Stress, whether it is from an exercise session or from a demanding job, stimulates the production of cortisol. You need some stress to react and respond to the challenges of everyday life. Prolonged, high stress maintains a dangerous level of circulating cortisol in your blood. This means the fat in your thighs is broken down and transported to be stored in the fat cells of your abdomen. Stressful situations cause your body to store body fat instead of burning body fat.
Considerations
While high-intensity interval training sessions are effective at burning plenty of calories, you are also at a greater risk of injury and overtraining. Include a mixture of high intensity and moderate intensity aerobic exercises to burn stored body fat. This combination increases the enzymes and the cell structures which help you become more efficient at burning fat and calories. Incorporating stress management techniques such as a midday nap or a 10-minute walk helps reduce the fat-storing potential of cortisol.
References
- "Exercise Physiology, Energy, Nutrition & Human Performance"; William McArdle, Frank Katch and Victor Katch; 2007
- "Strength and Conditioning Journal"; High-Intensity Interval Training: Applications for General Fitness Training; Brad Schoenfeld and Jay Dawes; December 2009
- "Strength and Conditioning Journal"; The Glycemic Index and Weight Control; R. Paul Gustafson, Ph.D.; June 2008
- "ACSM's Health & Fitness Journal"; Glycemic Index: An Educational Tool for Health and Fitness Professionals; Stephen Wong, Ph.D., et al.; November/December 2003
- "ACSM's Health & Fitness Journal"; Cortisol Connection: Tips on Managing Stress and Weight; Christine Maglione-Garves, et al.; September/October 2005
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