Can Diet and ExerciseReally Change Metabolism?

Resting metabolic rate (RMR; kcal/min) accounts for approximately 60% to 75% of total daily energy expenditure. The energy required to digest and absorb food, also called the thermic effect of feeding, provides an additional 5% to 10%, and the energy expended in physical activity (thermic effect of activity) comprises approximately 20% to 30% of daily energy output. The major determinants of RMR include such factors as body surface area, age, gender, thyroid hormones and catecholamines, genetics, body temperature, and in women, the phase of the menstrual cycle. Most factors are beyond the control of the individual, yet it is believed that voluntary behaviors, specifically dietary intake and exercise, can influence resting metabolism--but for how long and by how much is not well-defined. In general, it is widely believed that dieting decreases metabolic rate and exercise increases it. However, present research suggests that any change may be short-term. Also, the relationship of diet, exercise, and metabolism is not a simple one. Very restrictive diets can result in a transient decrease in metabolic rate. Whether this decrease is sustained has not been clearly shown. Many believe that a permanently reduced metabolism is the reason that diets do not work and that weight regain after weight loss seems inevitable. Current research efforts are focused on ways to maintain or increase metabolic rate through diet and exercise.