Food And Nutrient Needs
Although food intake tends to decrease with age as a function of social, psychological, and physiological changes, distinct requirements exist for a range of nutrients to compensate for age-related changes in absorption, utilization, and excretion (ADA). For example, even though energy needs decline with age because of decreased basal metabolism, reduction in lean body mass, and a more sedentary lifestyle (Ausman and Russell), it becomes difficult to ensure adequate diet quality (Blumberg) when daily energy intake is too low (less than 1,500 calories or 6.3 megajoules). Furthermore, protein requirements exceed those of younger adults (1.0 to 1.25 gram/kilogram versus 0.8 gram/kilogram body weight, respectively) (Garry and Vellas), which argues for continued consumption of sufficient intakes of high-quality protein food. Finally, even though vitamin A requirements lessen with age, other nutrient needs may increase.
In addition to appropriate intakes of energy and high-quality protein, and sufficient complex carbohydrates and fats (especially the mono- and polyunsaturated fats), older people require specific levels of micronutrients (vitamins and minerals) to ensure metabolic function and overall health. Also, since degenerative changes of aging are believed to result, in part, from the oxidative destruction of cells and tissues, much recent study has centered on the risk-lowering properties of antioxidant nutrients that may protect against such damage at the cellular level (Masaki et al.). Emerging research thus is now targeting nutrients found in a group of common foods, many of which have antioxidant properties. These so-called functional foods are ordinary foods eaten in usual quantities.
Micronutrient requirements, published as the dietary reference intakes, or DRIs (NAS), were revised in 2001 for all age groups (see Table 1), and new evidence is emerging on the potential protective nature of adequate intake levels of specific vitamins and minerals in aging individuals. Nutrients such as folic acid, riboflavin, and vitamins B6, B12, and C may prevent some age-related decline in memory loss (Rosenberg and Miller), and reduce risk for vascular disease. Adequate calcium is needed to prevent osteoporosis, and vitamin D can have favorable effects on muscle strength, bone mineral, and fracture risk (Heaney). Vitamins A and C and zinc are essential for competent immune system response and wound healing (Chandra). The antioxidants alpha-tocopherol (vitamin E), beta-carotene, and vitamin C may have consequences for aging and longevity (Hallfrisch et al.). These nutrients may also protect against cataract formation and age-related macular degeneration (Jacques), and the carotenoids lutein and zeaxanthin may protect the retina (Blumberg). Vitamin E in foods or supplements helps lessen risk of developing disorders such as Alzheimer's dementia and Parkinson's disease (Perkins et al.) as well as atherosclerosis (Kromhout). Vitamin K helps maintain bone density and lowers risk of reduced bone mass (Ferland). Sufficient dietary fiber is essential for prevention and/or treatment of constipation, hemorrhoids, diverticulosis, hiatal hernia, varicose veins, diabetes, elevated blood lipids, and obesity, and adequate fiber intake has also been related to decreased rates of heart disease and cancer (Ausman and Russell). Finally, adequate fluid intake is essential to prevent dehydration, which results in constipation, fecal impaction, cognitive impairment, functional decline, and, in extreme cases, death.
A varied diet can provide nutrient balance and adequate quantities of healthful foods. Physical activity, wise food selection, and greater intakes of enriched foods help increase total intake, nutrient density, and micronutrient levels. The modified Food Guide Pyramid was developed in the United States for people over the age of seventy to help them select appropriate foods (Russell et al.). This guide emphasizes nutrient-dense foods, dietary fiber, sufficient fluid intake, and the role of dietary supplements in maintaining adequate nutrient intakes. Recommendations include eating whole-grain cereals and breads; dark green, orange, and yellow fruits and vegetables to favor those with high levels of antioxidants; and using low-fat dairy products. The narrower base of the modified pyramid reflects the decreased needs for energy (calories) among older people.