Why Do We Gain Weight as We Age?

As we age, a decrease in our physical abilities leads to a decrease in our metabolic rate (amount of energy used in a given period), which in turn contributes to weight gain. The physiological changes that accompany increasing age affect the body's composition and cardiopulmonary (heart and lung) function, thus reducing our ability to work and exercise and lose weight. Genetics, muscle mass, gender, calorie consumption versus expenditure, and lifestyle are all factors in weight gain.

Changes Occurring with Age
A decline in our physical abilities starts around age 30, continues throughout our life, and reaches a plateau between ages 60 and 70. After the plateau, a slower decline follows. The rate of decline varies with our individual level of fitness as well as our lifestyle. The speed at which our nerves conduct impulses declines approximately 15%, resulting in decreased reaction time and slowness in performing tasks. Maximum breathing capacity decreases approximately 40% during this period. Individuals with chronic lung disease, such as emphysema, suffer a more significant decline. Cardiovascular function declines approximately one half of one percent each year starting around age 30. It is no coincidence that many world-class and endurance athletes begin gradually leaving their sport after this age. There is a 40% to 50% reduction in muscle mass during this period with a similar decline in bone mass. There is a simultaneous increase in body fat in both men and women. The metabolic rate also declines with age. This decline is mostly affected by muscle mass. Regular exercise helps to preserve muscle mass, particularly muscle loading exercises such as weight training, walking, and physically challenging occupations.

Behaviors such as frequent dieting have been shown to affect the resting metabolic rate and your weight. Individuals who diet frequently have a significant decline in their basal metabolic rate. This decline is prolonged and sustained for several months and cannot be attributed to that expected from a loss in muscle mass or fat free mass. Periods of extreme starvation can produce as much as a 45% decline of the metabolic system. Studies have shown that calorie restriction in short-lived animal species not only causes a decrease in the basal metabolic rate but also an increase in lifespan. Studies are now underway to evaluate calorie restriction in humans and its effect on longevity.

Physical activity refers to body movements that result in the production of energy. The type, frequency, and duration of activity, as well as rate of progress, should be considered when choosing an exercise program. Physical activity has been shown to decrease the occurrence of some chronic diseases. There is a large body of evidence that the risk of death from disease is decreased in individuals who are physically active. The strongest evidence of this has been shown for coronary artery disease. There is moderate evidence that physical activity decreases the risk of hypertension, obesity, colon cancer, noninsulin-dependent diabetes, and osteoporosis. Physically active individuals have been shown to perform daily activities with less effort.

General Comments
Our organ systems, such as the visual, auditory, and endocrine systems, appear to decline with age. A decline in the water content of our ligaments and tendons contributes to inflexibility and may further limit our physical abilities. However, the basal metabolic rate is clearly affected most by the decline in muscle mass, the individual's lifestyle, and underlying health. Despite these limitations, a decline in all physical abilities is not inevitable. Studies show that healthy individuals of all ages can increase their muscular strength and endurance to a proportionate degree. In fact, strength in a study group of healthy men and women ages 62 to 84 improved by as much as 57% over a brief training period.

Unfortunately, there is not an age-related decline in appetite. Most individuals consume calories in excess of requirements, resulting in weight gain over the years. To prevent this age-related gain in weight, considerable motivation is required. One has to avoid the imbalance between calorie consumption and expenditure and consider the effects of aging while maintaining a healthy lifestyle.

William E. Roundtree, MD
Columbus, Georgia