1. Physiological and metabolic characteristics of the elderly (1) Metabolic function decreased. (2) Changes in body composition. The main manifestations are: decreased cell mass, decreased water in the body and decreased bone minerals. (3) The changes of organ function mainly include: the decrease of digestive juice, digestive enzymes and gastric acid secretion in the digestive system; The decline of heart function, brain function, renal function and liver metabolic ability all decrease with age. Secondly, there are many theories about the relationship between dietary nutritional factors and aging, among which the free radical theory is more concerned. According to the theory, the oxidation reaction of human tissues will produce free radicals, which are unstable and can interact with biological macromolecules in the body to produce peroxides, which will destroy cell membranes and then affect cell functions. Free radical damage is mainly manifested by lipid peroxidation. Under normal circumstances, there are two kinds of antioxidant systems in human body, namely, non-enzymatic defense systems such as antioxidant nutrients such as VC and VE, and enzymatic defense systems such as SOD and GSH-PX. Third, the nutritional needs of the elderly (1) Heat energy Due to the decline of basal metabolism, physical activity is reduced, the proportion of adipose tissue in the body is increased, and the heat energy needs of the elderly are relatively reduced. After the age of 60, it will be reduced by 20% compared with the youth, and it will be reduced by 30% after the age of 70. RNI: Group 60 ~ light manual labor, male 7.94MJ/d, female 7.53 MJ/d.. (2) Middle-aged and elderly people in protein are prone to negative nitrogen balance because catabolism is greater than anabolism. Therefore, the intake of protein should be sufficient and of high quality. Protein should account for 12~ 14% of the total thermal energy, RNI: 70 years old ~ group, male 75g/d, female 65g/d. (3) Obese elderly people have poor digestion ability of fat, so they should not consume too much fat. Generally, fat heating accounts for 20% of the total heat energy, mainly vegetable oil rich in polyunsaturated fatty acids. (4) Carbohydrate, due to impaired glucose tolerance in the elderly, insulin secretion is reduced, and the ability to regulate blood sugar is low, which is easy to increase blood sugar. Therefore, the elderly should not eat foods with high sucrose content to prevent blood sugar and blood lipid from rising. Fruits, honey and other foods containing high fructose should not be eaten. We should eat more vegetables and increase the intake of dietary fiber to enhance intestinal peristalsis and prevent constipation. (5) Minerals 1. Adequate calcium is very important for the elderly. Because the elderly's ability to absorb calcium decreases, physical activity decreases and bone calcium deposition decreases, the elderly are prone to negative calcium balance, and osteoporosis is more common. Ai of calcium:1000 mg/d; /d over 50 years old; 2. Iron is prone to iron deficiency anemia because the ability of the elderly to absorb and utilize iron decreases, the hematopoietic function decreases, and the HB content decreases. AI in China; The group over 50 years old 1.5 mg/d should pay attention to choosing foods with high heme iron content. 3. Selenium is an antioxidant, and the elderly should pay attention to dietary supplement. In addition, trace elements such as zinc, copper and chromium are equally important. (VI) Vitamins In order to regulate metabolism in the body and enhance disease resistance, the intake of various vitamins should reach the recommended intake in China. VE is an important antioxidant vitamin. When VE is deficient, cells in the body can appear a kind of brown pigment particles, which become brown pigments, which are deposited after some components of cells are oxidized and decomposed, and accumulate in the body with the aging process, becoming senile plaques. Vitamin E supplementation can reduce the formation of lipofuscin in cells. The AI of the elderly is14 mg/d. Adequate VC can prevent arteriosclerosis in the elderly, make cholesterol metabolism easy to be excreted and enhance resistance, so the supply should be fully guaranteed. The daily RNI of the elderly is 100 mg.