① Physical changes. It is characterized by increased wrinkles, white hair, fatty brown spots, senile warts, unstable gait, slow movement, pudgy and so on. ② Changes of body composition. The total amount of metabolic tissues decreases with age, and the proportion of tissues with metabolic function in old age (30%) is only half of that in adolescence (60%). The total cell mass decreased, muscle atrophy, water decreased, bone density decreased and fat increased. ③ Metabolic decline. Anabolism decreases, catabolism increases, and basal metabolism decreases; Impaired glucose tolerance and elevated blood lipids. (4) organ function decline, digestive, circulatory, urinary, endocrine, reproductive, joint, exercise, nervous system function decline.

(2) Dietary principles of the elderly

In addition to strictly implementing the principles in the Dietary Guidelines for China Residents, the elderly should also follow the following principles in the Dietary Guidelines for Specific Groups: ① Food should be thick and thin, which is easy to digest. ② Take an active part in moderate physical activity and keep energy balance.

(3) Specific dietary measures

① Eat more coarse grains, soybeans, vegetables and fruits, and pay special attention to plant foods, because coarse grains contain more dietary fiber, vitamin B 1, vitamin E and minerals. The latter three foods contain a variety of antioxidant nutrients, such as vitamin E, vitamin C, carotenoids, zinc, selenium, copper, manganese, polyphenols, polysaccharides and isoflavones. These foods are good for delaying aging. ② Stick to a glass of milk and an egg every day, and eat fish, poultry, lean meat and seafood in moderation, because these foods can provide high-quality protein and unsaturated fatty acids. Milk is a high-quality calcium source, and seafood is rich in iodine, which plays an important role in regulating body metabolism. Eat less or not eat meat oil, fat, fried food, dessert, viscera, fish eggs and other foods, because these foods contain high energy, cholesterol and saturated fatty acids, which can promote aging and cause damage to the body. (4) Pay attention to color, fragrance, taste and shape, promote appetite, and be suitable for the chewing and digestive functions of the elderly. The number of meals per meal and the proportion of energy can vary from person to person, and the energy intake should not be too much. It is appropriate to have 70% full and appropriate weight for each meal. Middle-aged and elderly people should pay special attention to a balanced diet, especially when they are under stress, such as staying up late, being mentally stimulated and getting sick.

(4) Common nutritional problems of middle-aged and elderly people.

① Micronutrient deficiency. Calcium deficiency, middle-aged and elderly people are easy to cause calcium deficiency, osteoporosis and fracture, osteoporosis and tooth loss; The middle-aged and elderly people are deficient in iron, insufficient in intake, underutilized in vitamin C and iron, and the incidence of anemia is significantly higher than that of adults. High sodium and low potassium, poor taste of the elderly, more sodium intake, easy to store water and sodium, easy to cause hypertension. ② Energy imbalance. It is characterized by excessive weight gain or loss, that is, obesity or emaciation. ③ Nutritional diseases. With the increase of age, the resistance decreases, and the nutritional diseases of middle-aged and elderly people also increase, such as diabetes, hypertension, cardiovascular diseases, constipation, gastrointestinal dysfunction and so on.