Dietary principles for longevity in the elderly: Matching dietary fiber with digestive function and dietary classification guidelines for clinical patients.

As people age, the physiological functions of various organs decline to varying degrees, especially digestion and metabolism, directly affecting nutritional status. For example, tooth loss, reduced digestive juice secretion, and slowed gastrointestinal motility decrease the body's absorption and utilization of nutrients. Therefore, older adults must obtain sufficient nutrients, especially micronutrients, from their diet. Given the decline in gastrointestinal function, older adults should choose easily digestible foods to facilitate absorption and utilization. However, food should not be overly refined; a balance of whole grains and refined grains is essential. On the one hand, staple foods should include a mix of whole grains and refined grains. Whole grains such as oats and corn contain more dietary fiber than rice and wheat. On the other hand, food processing should not be overly refined, as excessive processing of grains leads to the loss of a large amount of dietary fiber and vitamins and minerals contained in the endosperm of the grain. Dietary fiber increases intestinal motility, helping to prevent constipation in the elderly. Dietary fiber also improves the gut microbiota, making food easier to digest and absorb. Recent studies have also shown that dietary fiber, especially soluble fiber, plays a role in improving blood sugar and lipid metabolism, functions that are particularly beneficial for older adults. As people age, the incidence of non-communicable chronic diseases such as cardiovascular and cerebrovascular diseases, diabetes, and cancer increases significantly. Dietary fiber is also beneficial for the prevention of these diseases. The basal metabolism of the elderly decreases, and they are prone to overweight or obesity from the early stages of old age. Obesity will increase the risk of non-communicable chronic diseases. Therefore, the elderly should actively participate in appropriate physical activities or exercises, such as walking and Tai Chi, to improve their various physiological functions. However, because the blood vessels of the elderly have reduced elasticity, increased blood flow resistance, and reduced cardiovascular and cerebrovascular function, they should not engage in excessive activities. Otherwise, if they exceed the cardiovascular and cerebrovascular capacity, they will damage the function and increase the risk of such diseases. Therefore, the elderly should pay special attention to the reasonable adjustment of the balance between food intake and physical activity to maintain their weight within an appropriate range. Regular diet: (1) Regular food: This is a balanced diet with sufficient energy supply, complete nutrients, and appropriate proportions. It is suitable for patients in the recovery period of diseases with normal body temperature, no digestive problems, and no need to restrict their diet. When cooking, pay attention to the color, aroma, taste, and easy digestibility of the food. (2) Soft food: This is a diet that is made softer and easier to digest than regular food. Suitable for patients in the recovery period of enteritis and after rectal, colon and anal surgery, patients with poor chewing ability, patients in the recovery process of various diseases and the elderly and children. A little snack can be added. (3) Semi-liquid: a multi-meal diet that is easier to digest than soft rice. Suitable for patients with digestive tract diseases, shortly after surgery, with high fever and weak body. (4) Liquid: a liquid diet with low residue. Due to the incomplete nutritional components and low energy, it is not suitable for long-term consumption. It is only suitable for some patients with acute infectious diseases, high fever, difficulty swallowing, and postoperative patients. Special diet: (1) High-energy diet and low-energy diet: High-energy diet is suitable for underweight patients, such as patients with tuberculosis, hyperthyroidism and others, and those who need to gain weight during the recovery period after illness; low-energy diet is suitable for patients with simple obesity, hypertension and endocrine disorders. (2) Low-cholesterol diet and low-oil diet: suitable for patients with liver, gallbladder and pancreas diseases, hyperlipidemia and cardiovascular diseases. The daily cholesterol intake of a low-cholesterol diet should be less than 300mg. The daily fat intake of a low-oil diet can be limited to less than 50g, 40g or 20g as needed. (3) Low-protein diet: suitable for patients with acute glomerulonephritis, uremia and liver failure, limiting the daily protein intake to 20-40g. For patients with renal dysfunction, wheat starch should be combined with eggs and milk to improve the quality of protein intake; patients with liver failure can choose soy protein rich in branched-chain amino acids. (4) Low-salt, salt-free and low-sodium diets: these three diets are suitable for patients with congestive heart failure, acute nephritis, cirrhosis with ascites, hypertension, preeclampsia, etc. Choose one of them according to the severity of the condition. Low-salt means a daily intake of 2g of salt or 10ml of soy sauce; low-sodium means a daily intake of less than 500mg of sodium, and low-sodium foods are required. (5) High-iron diet and high-calcium diet: The high-iron diet is suitable for patients with iron deficiency anemia, and the daily intake of iron should be more than 25mg; the high-calcium diet is suitable for patients with osteoporosis, vitamin D deficiency, limb replantation, etc., and the daily intake of calcium should be more than 2g.