Resistance training exercise has many benefits for health, fitness and performance. Exercise that builds muscle can speed up your basal metabolism, resulting in an increased caloric burn throughout the day. But restricting calories to lose weight can cause your metabolism to slow down, even if you keep exercising. Learning more about how diet and exercise influence your metabolism will help you train and eat smarter for optimal results.
Metabolism, the sum total of daily energy expended by an individual each day, can be broken down into three components: resting metabolic rate, or RMR, thermic effect of physical activity, or TEPA, and thermic effect of food, or TPF. TPF includes the energy required to digest the food you eat each day, and accounts for about 10 percent of your daily caloric expenditure. RMR is the amount of energy required for your body to perform basic functions of metabolism at rest, and accounts for 60 to 75 percent of your daily energy expenditure. TEPA is the amount of energy burned for physical activity, including exercise, and accounts for 15 to 30 percent of your daily caloric expenditure. Both RMR and TEPA are influenced by the amount and type of exercise you do.
Fat Free Mass and Metabolism
Your fat-free mass, also referred to as lean mass, is your total mass minus your fat mass, and includes bones, muscles and other body tissues that are not fat. Fat-free mass, or FFM, is measured by body composition assessments. Fat free mass has a profound effect on your resting metabolic rate. A 2005 study by Johnstone, et al, published in the "American Journal of Clinical Nutrition" found fat-free mass to be the dominant factor influencing differences in basal metabolism between individual subjects.
Exercise and Metabolism
Physical activity affects your daily metabolism in the short run by increasing your TEPA, and in the long run by increasing your FFM, which in turn affects your RMR. According to exercise scientist Len Kravitz, PhD, resistance training that leads to an increase in lean muscle tissue increases your RMR because lean muscle requires a high energy demand to maintain itself at rest. Resistance training can help prevent the loss of FFM during a restricted-calorie weight loss program.
Calorie Restriction and Metabolism
When you reduce your caloric intake, your metabolism slows down to maintain equilibrium. A 2007 study of non-obese adults published by Martin C.K., et al in "Obesity" found that modest caloric restriction resulted in a corresponding decrease in RMR. A 2012 study of obese subjects by Johannsen, et al, published in the "Journal of Clinical Endocrinology and Metabolism," found that exercise that preserved FFM was not enough to prevent the metabolic slowing associated with calorie restriction. The researchers cautioned that continued high levels of physical activity and caloric restriction may be necessary to prevent weight re-gain after a restricted-calorie weight loss program.
- American Journal of Clinical Nutrition: Factors Influencing Variation in Basal Metabolic Rate Include Fat-Free Mass, Fat Mass, Age, and Circulating Thyroxine
- IDEA Health and Fitness Association: Controversies in Metabolism
- Obesity: Effect of Calorie Restriction on Resting Metabolic Rate and Spontaneous Physical Activity
- University of New Mexico: Getting a Grip on Body Composition
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