Nutrition, Malnutrition, and Feeding Issues

Reduced Metabolic Rate

The most dramatic physiological change that affects nutrition occurs in body composition. Lean body (muscle) mass decreases and fat content increases naturally over the decades of life. This situation is preventable with nutritional balance and exercise. Muscle mass is slowly lost because there is a reduction in protein synthesis and an inability for the body to retain by-products for efficient muscle production as the body ages. Loss of muscle mass (or sarcopenia) begins after 25 years of age and accelerates after 45 years of age. The development of sarcopenia is multifactorial in origin and is due to a reduction of motor neurons, a decrease in anabolic hormonal influences, and disuse atrophy. Sarcopenia influences muscle strength, gait, and balance and also contributes to the increased risk of falls and frailty. The biggest impact of sarcopenia on nutrition is reduced energy requirements and metabolism. This reduction in metabolic rate can be countered by increasing exercise and protein intake to maintain healthy muscle mass. Particular attention must be given to the increase in protein requirements of the older adult because proteins are not produced or used as efficiently by the aging body. In general, 1 milligram per kilogram (mg/kg) of body weight per day of protein consumption is considered to be adequate.

The composition of body fat also changes in quantity and location. Body fat increases over time and is associated with metabolic consequences such as insulin resistance, elevation of triglycerides, and an increased risk of diabetes or hypertension. There is a linear increase of total body fat mass between 40 and 80 years of age. The distribution seems to favor a truncal, abdominal, and visceral distribution. This centripetal distribution is associated with an increased risk of those conditions noted previously and cardiovascular disease. Despite the natural propensity for these changes, lifestyle interventions of diet and exercise can delay the process by preserving muscle mass, in turn reducing fat production. Resistance exercises focus on strengthening and rebuilding larger muscle groups not only to increase metabolic rate but also to improve functional status.

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