Changes in Metabolism and Body Composition

Maintaining a healthy body weight and body fat percentage throughout your adult life is key to maintaining health and fitness as you age. This often seems easier said than done, considering basal metabolic rate (BMR, see Chapter 1) declines as you age.

With aging, expect to see a gradual decline in BMR, possibly resulting in needing 100 fewer kcal a day with each passing decade.

Taken from Tufts University Health and Nutrition Letter. November 1998; 16(9): 6.

The loss of muscle mass as you age is directly responsible for the decline in BMR. Muscle is metabolically active, which means that it requires a set number of kcals each day to maintain its mass. On average, people begin to lose some muscle mass after the age of 35 years. This results in fewer metabolic demands and less total daily kcal requirements. However, the amount of muscle mass that you lose is dependent upon how much physical activity you perform as you age, particularly activities that require muscle strength such as strength training. By engaging in strength training exercises you will preserve and possibly gain muscle mass, leading to a 10% to 15% boost in your BMR!

Along with a decrease in muscle mass, inactivity can also lead to an increase in body fat. This occurs if the number of kcals consumed is greater than the number of kcals expended through physical activity, as explained in the energy balance equations in Chapter 1. This simultaneous increase in body fat and decrease in muscle mass leads to a greater body mass index (BMI) and is associated with an increased risk for heart and blood vessel diseases, obesity, diabetes, and other diseases (see Chapter 1).

Any alterations in energy expenditure, either through changes in BMR or changes in physical activity level, need to be countered by changes in kcal intake to keep your net energy balance at zero and to maintain your current body weight. Therefore, a combination of sound nutritional practices and regular physical activity will enable you to maintain a healthy body weight and body composition and remain physically fit as you age.

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