Question: I have heard that one of the biggest advantages of exercise for losing weight is that there is a residual effect after exercise where the metabolic rate remains fairly high for a period of time. How many calories do you burn after exercise as compared to during exercise? I enjoy your column.
Answer: Several studies have shown that vigorous exercise causes a rise in metabolic rate following exercise. The amount of this increase varies from 9 to 25 percent, and the effects may last for six to 15 hours.However, this type of increase came from two hours of strenuous football, walking 10 miles at a 15-minute per mile pace or riding 11/2 hours on a stationary cycle at 70 percent of your aerobic capacity. Most people can't or don't exercise at these levels of intensity or for such long durations.
The effects of low to moderate levels of exertion are not nearly as substantial. In fact, you have to exercise at least 20 minutes at 70 percent of aerobic capacity (about 80 percent of maximum heart rate) or work for a long period of time to increase your metabolic rate to any great extent. For instance, subjects who worked at 50 percent of aerobic capacity for three hours experienced significant increases in metabolic rate after exercise.
One of the really important benefits of using exercise in a weight loss program relates to maintaining lean tissue (muscle) as you lose weight. Since muscle is more metabolically active than fat, the more you have, the higher will be the metabolic rate at rest - and resting metabolic rate accounts for about 70 percent of the total calories you use. People who use diet only as a means of losing weight often lose a substantial amount of muscle tissue. This tends to lower metabolic rate and makes it even more difficult to lose weight.
The long-term effects of regular exercise are really impressive, even without any residual. For instance, a 250-pound person who walked only a half-hour a day could easily burn more than 100,000 calories in a year. At 3,500 calories per pound of fat, this could account for a potential loss of almost 32 pounds. Ten years of regular activity can make an impressive difference, especially if a healthy diet is eaten.
A study several years ago by the Stanford Center for Research in Disease Prevention evaluated the dietary habits of 155 moderately overweight men. Their diets were typical of all American diets, containing about 40 percent calories from fats, about 40 percent calories from carbohydrates, 6 percent of calories from alcohol and the rest from protein. These researchers found a direct correlation between percent body fat and the amount of total fat, saturated fatty acids and monosaturated fatty acids they consumed. No relationship was established between total calories consumed and total weight or percent body fat.
The message seems clear. To control body weight, exercise regularly, lower the amount of fat in your diet and eat lots of complex carbohydrates.
Garth Fisher is director of the Human Performance Research Center at Brigham Young University.