Encyclopedia of Family Medicine

Chapter 4 Human Body and Nutrition (4)
Our ancestors have long noticed that there is a very close relationship between people's diet and medical treatment and health.As early as 2000 years ago, it was recorded in relevant historical books. For example, in the "Huangdi Neijing Suwen", food is divided into four categories, and it is represented by "nourishing", "helping", "benefiting" and "charging". The nutritional value of each type of food and the reasonable proportion in the diet.It also puts forward the understanding of "eating moderately..., eating at the right time, and satisfying hunger and fullness" and so on.However, in the long course of historical development, various prejudices have also appeared.When some people talk about nutrition, they emphasize eating more animal foods such as fish, meat, eggs, milk, etc., thinking that the more such foods are eaten, the better the nutrition, which is not in line with the concept of a balanced diet.The human body needs nutrients in many ways, and there are certain requirements. Frequent consumption of too much animal food is not good for human health, and it often becomes an inducement for certain tumors and cardiovascular diseases.Others believe that the more expensive the food, the better the nutrition, which is also due to the incomplete understanding of nutrition knowledge.Because, from a nutritional point of view, the nutritional value and price of food are not always parallel.On the contrary, some cheap foods have higher nutritional value.Such as carrots and bamboo shoots.

So, what is considered nutritionally reasonable?From a nutritional point of view: it means that the various nutrients provided by three meals a day can meet the needs of human growth, development and various physiological and physical activities, that is, the dietary allocation is reasonable to achieve the purpose of dietary balance.The staple food can be thick or thin, and the non-staple food can be meat or vegetable. There must be animal food and soy products, as well as more vegetables and fruits.In this way, reasonable nutrition can be formed.

Effects of poor eating habits

In real life, the intake of nutrients is not only affected by improper dietary preparation and unreasonable cooking, but also related to various bad eating habits.Usually there are several types:
(1) Snacks: Many children eat melon seeds, candies and other foods all day long. There is no normal eating pattern. The digestive system has not established the conditioned reflex to eat regularly, so that the gastrointestinal tract cannot rest, which can cause loss of appetite and affect eating. .Over time, resulting in a variety of nutrient deficiencies.

(2) Partial eclipse: For those who do not like meat dishes, the source of high-quality protein will be greatly limited; for those who eat meat dishes, it will lead to excess calories and lack of various vitamins and inorganic salts.

(3) Overeating: Overeating can not only cause gastrointestinal disorders, but also induce various diseases.Such as acute gastric dilatation, gastroptosis and so on.Greasy food forces a large amount of bile and pancreatic juice to be secreted, which may cause biliary tract disease and pancreatitis.These diseases can seriously affect the body's intake of nutrients.

(4) Fast food: "Gobble up" not only increases the burden on the stomach, but also prone to gastritis and gastric ulcer.Moreover, due to poor chewing of food, it will inevitably lead to incomplete digestion and absorption of food, resulting in the loss of various nutrients.

(5) Hot food: too hot food can easily burn the tongue, oral mucosa, esophagus, etc.It can also cause damage to teeth.Scarring and inflammation from burns to the esophagus can interfere with the absorption of nutrients.

(6) Salty food: People who like to eat salty food consume much more salt than normal people need.Due to the retention of sodium in the body, the increase in body fluids and blood circulation increases the burden on the heart and kidneys, which can cause hypertension and other diseases.

Types and functions of nutrients

Nutrients refer to the essential substances contained in food that can maintain the survival and health of the body, and ensure growth and labor capacity.These substances can be roughly divided into seven categories: protein, fat, carbohydrates (also known as sugars), vitamins, minerals (trace elements), water and dietary fiber, and there are dozens of them.

There are three main functions of nutrients:
(1) Supply heat energy: protein, fat, and carbohydrates are all nutrients that supply heat to the human body.

(2) Forming body tissues: Proteins, fats, carbohydrates and certain inorganic salts can form body tissues through metabolism and assimilation to meet the needs of human growth, development and metabolism.

(3) Regulate physiological functions: some nutrients play a regulatory role in the physiological activities and biochemical changes of the body, so that they can be carried out in a balanced and coordinated manner.Such as inorganic salts and trace elements, vitamins, proteins, some carbohydrates have this function.

Various nutrients have special functions in the metabolic process of the body.Generally, they cannot replace each other, but they are closely related to each other and can complement each other.Therefore, it is necessary to maintain the balance of nutrient supply and meet their respective needs.

Meal Plan for Different Ages

学龄前儿童：每日主食200~250克，大米、面粉、玉米粉、小米、红豆、绿豆等调换混合食用；牛奶或豆浆250克；肉类50克，包括牛、羊、猪、禽、鱼类或大豆制品；蛋1个；青菜及水果200~300克；糖20克左右；烹调油15克。

学龄儿童：每日粮食300~400克；牛奶或豆浆250克；肉类50~100克（无肉、鱼时可用大豆制品）；鸡蛋1~2个；青菜500克；有条件的最好每日吃水果1~2个；烹调油25~40克。主食应粗细粮、豆类等搭配吃，以提高蛋白质的利用率。如蒸红豆饭、绿豆粥、玉米面加黄豆粉的发糕等都是增加蛋白质互补作用的食品。副食也要荤、素搭配。

青年和壮年：每日主食400~600克，同样应粗细粮搭配。如豆饭、豆包，加黄豆粉的发糕，可吃一些红薯；肉类、鱼类、蛋类每日平均100克；黄豆及其制品50~100克；蔬菜500~750克；烹调油25~50克。青春期男女，最好每日能保证1个鸡蛋。

中年和老年：每日主食250~350克，多吃五谷杂粮；牛奶250~500克（或牛奶250克、豆浆250克）；瘦肉或鱼、禽类100~150克（或肉、鱼类100克，鸡蛋1个）；豆腐100克；新鲜蔬菜400~500克；水果1~2个；烹调油（植物油）25~30克。由于中、老年人易发胖，糖和脂肪的摄入量应比青、壮年少，还应少吃精制糖（白糖、糖果等），少用盐。

Protein is an important material basis of the human body
Protein is an essential component of all cell and tissue structures.It is the most important material basis of human life activities.In human cells, protein accounts for about 1/3, and the average adult body contains about 16% protein, about 3% in skin and skeletal muscle, about 80% in collagen, and about 25% in blood. Second only to moisture.Protein is composed of different amino acids, some of which can be synthesized by the human body, called non-essential amino acids; and about eight other amino acids must be supplied by food, called essential amino acids.If the food contains a complete range of essential amino acids, and the quantity is large, the nutritional value of this food protein is high.Such as beef, eggs, fish, soybeans, etc., which are rich in complete protein, so the nutritional value is high.The protein contained in foods such as rice noodles is incomplete protein, so the nutritional value is lower.Therefore, a monotonous diet will cause malnutrition.Pay attention to the combination of various foods at ordinary times, and you can play the complementary role of protein.Experiments have shown that the food with the highest nutritional value is a mixture of 5% egg white and 35% potato protein.

The main functions of protein in the human body are:
(1) Constitute enzymes, hormones, antibodies and body tissues.

(2) Promote human growth and development.

(3) Maintain capillary osmotic pressure.

(4) Supply some energy to the human body.

protein is life

The human body needs to take in a certain amount of protein through food every day to meet the needs of body growth, renewal, tissue repair and various physiological functions.That is to say, the production, existence and demise of life are all related to protein.

The nerves, muscles, blood, bones, and even hair of the human body do not contain protein.A baby weighing several kilograms grows into an adult weighing tens of kilograms, and the self-renewal of various tissue components in the body is inseparable from protein.The metabolism of the human body is realized through thousands of chemical reactions, and these reactions need to be catalyzed by enzymes. Enzymes can widely participate in various life activities of the human body at normal body temperature.Such as muscle contraction, blood circulation, breathing, digestion, growth, development and reproduction, and various thinking activities.Without the participation of enzymes, life activities cannot proceed.And these enzymes with various specific functions, like some hormones that regulate physiological functions, are also proteins themselves.

It can be seen that proteins are ubiquitous in life activities and have a variety of important functions.Once the organism loses protein, all life activities will stop and life will end.Therefore, protein is a living substance.

protein intake

How much protein a person needs every day depends on age, sex, working conditions and health, and varies by food source.For example, a healthy adult man weighing 65 kg needs about 75-100 grams of protein per day according to the intensity of his physical labor.Generally, adult women are slightly less.Children and adolescents need more protein during their growth and development, as well as women's pregnancy and lactation periods.As for people who are sick, such as burns, fractures, infections, nephritis, etc., the patient's protein requirement can be increased or decreased according to the condition.

An adult man with a weight of 65 kg and engaged in light labor can obtain 500 grams of his daily staple and non-staple food (100 grams of grain, 50 grams of meat, one egg, 500 grams of bean products, and 75 grams of vegetables) protein.According to needs and possibilities, he can also adjust non-staple food appropriately, such as adding some milk, eggs, meat, soy products, peanuts, etc. to improve the quality and quantity of protein.If properly prepared, the "complementary effect" of various plant proteins can be fully utilized, and the need for protein can be guaranteed by adding less or even no animal food.

Other children, adolescents, adults, elderly men and women, pregnant women, parturients and patients can use this as a reference to adjust their daily staple and non-staple foods, and increase or decrease protein intake as appropriate.

Food Protein Choices
When we choose protein food, we should first consider the protein content.If the protein content in the food is very small, even if the nutritional value is high, it cannot meet the needs of the human body.In every 100 grams of food commonly used, meat contains 10-20 grams of protein, fish contains 15-20 grams, whole eggs contain 13-15 grams, beans contain 20-30 grams, cereals contain 8-12 grams, vegetables , fruit containing 1 to 2 grams.Animal foods are more abundant than plant foods.Beans have a lot of content, and their quality is not worse than that of animal foods.There are three points to judge the quality of protein: (1) The more thoroughly the protein is digested and absorbed by the human body, the higher its nutritional value will be.The digestibility of whole soybeans is 60%, which can be increased to 90% after being made into tofu and soy milk. The absorption rate of other proteins can also be improved after being cooked, such as 98% for milk, 93% for meat, and 98% for eggs. 82%, rice is 2%. (94) The degree of utilization of protein absorbed by the human body varies from high to low. The higher the degree of utilization, the higher the nutritional value.The degree of utilization is called the physiological value of protein.The physiological value of commonly used food protein is: eggs 85%; milk 83%; fish 77%; shrimp 76%; beef 77%; rice 76%; cabbage 67%; wheat 3%.The physiological value of animal protein is generally higher than that of vegetable protein. ([-]) Check whether the essential amino acids contained are rich, complete in variety, and appropriate in proportion.Complete types, sufficient quantities, and appropriate proportions are called complete proteins, such as animal protein and soy protein.The variety is complete, but the proportion is not appropriate. It is called semi-complete protein, which is more abundant in grains.Incomplete types are called incomplete proteins, such as glial protein in meat skin and zein in corn.Mix two or more foods to make the amino acids contained in them complement each other and better meet the needs of the human body.Eating more protein is also not good, it will increase the burden on the kidneys and increase the consumption of extra energy, which is not economical.So, eat protein reasonably.

The importance of fat

Fat is an important part of the human body, and it is also the nutrient with the highest calorie content.Fat is a very important compound composed of carbon, hydrogen and oxygen elements.Some fats also contain phosphorus and nitrogen, which are essential substances for the construction, transformation and growth of body cells.The average body fat content of adult men in our country is about 13.3%, and that of women is slightly higher.Body fat content varies greatly due to nutrition and activity, and body fat can be reduced due to energy consumption when hungry.

Fat is commonly known as grease.According to the source, it can be divided into two categories: animal and vegetable oils.According to the chemical structure, it can be divided into fat (also known as neutral fat) and lipid.Lipids include phospholipids, glycolipids, sterols and sterol lipids.

Fat plays an important role in human nutrition, and 10-40% of the total energy required by the human body is provided by fat.The main function of fat is to supply calories, which is twice as much as protein and carbohydrates (sugars) of the same weight.In addition, it also provides "essential fatty acids" needed by the human body.There are many types of fatty acids, which can be divided into three categories: saturated, monounsaturated and polyunsaturated fatty acids.Linoleic acid, linolenic acid and arachidonic acid in polyunsaturated fatty acids cannot be synthesized in animals and humans and must be obtained from food, so they are called "essential fatty acids". The lack of them will produce a series of deficiency symptoms, such as growth retardation. , dermatitis, etc.Nutritionists have proposed that essential fatty acid calories should account for 1% to 3% of total dietary calories.These fatty acids are most abundant in soybean oil, corn oil, cottonseed oil, sesame oil, sunflower oil, and peanut oil.

The role of fat in the human body

Fat is mainly distributed in human subcutaneous tissue, omentum, mesentery and around the kidneys.Body fat content often changes with nutritional status, energy consumption and other factors.Its main physiological functions are:
(1) Supply heat energy.Fats contain more carbon and hydrogen than carbohydrates.Therefore, more heat can be released during oxidation. 1 gram of fat can release 9 kcal of heat energy, which is the one with the highest heat production among nutrients.

(2) Constitute human tissue.Phospholipids and cholesterol in fat are the main components of human cells, and are most abundant in brain cells and nerve cells.Some sterols are necessary for the manufacture of steroid hormones in the body.Such as adrenal cortex hormones, sex hormones and so on.

(3) Supply essential fatty acids.The essential fatty acids needed by the human body are provided by dietary fat.It is mainly used in the synthesis of phospholipids, which is an important part of all cell structures; maintaining the normal permeability of skin microvessels, as well as the role of sperm formation and prostaglandin synthesis, etc., are important functions of essential fatty acids.

(4) Increase appetite and promote the absorption of some vitamins.Foods with no fat or little fat are not tasty. Fatty foods can increase the flavor and promote the absorption and utilization of some vitamins A, D, E, and K dissolved in fat.

(5) Regulate body temperature and protect internal organs.Most of the fat is stored under the skin to regulate body temperature, protect temperature-sensitive tissues, and prevent heat energy from being lost.Fat distributes and fills the gaps of various internal organs, which can protect them from vibration and mechanical damage, and maintain the growth and development of the skin.

(6) Increase satiety.Fat is digested slowly in the stomach and stays for a long time, which can increase the feeling of fullness and make people less hungry.

animal oil vs vegetable oil

There are two indicators to measure the nutritional value of oil: one is the amount of unsaturated fatty acids; the other is the amount of essential fatty acids.Of course, the content of vitamins, the level of digestibility, storage performance, etc. should be fully considered.Here is a brief overview of the nutritional value of several commonly used oils:
Cod liver oil: Contains the highest amount of unsaturated fatty acids and is rich in vitamins A and D, but it cannot be used for cooking.

Butter and cream: high in saturated fatty acids and cholesterol, and vitamins A and D, but it is not good for patients such as hyperlipidemia.

Lard: Contains more saturated fatty acids and cholesterol, but does not contain vitamins A and D.Digestibility is also slightly lower than vegetable oils.

Butter and Suet: High in cholesterol, poor in digestion and absorption.

Sesame oil (sesame oil), soybean oil, peanut oil, rapeseed oil, corn oil, sunflower oil, tea oil and other vegetable oils.Contains more essential unsaturated fatty acids, which can lower blood cholesterol and reduce the risk of arteriosclerosis.Some vegetable oils contain anti-oxidant vitamin E or sesamol, which improves storage.

It can be seen that the amount of unsaturated fatty acids and essential fatty acids contained in vegetable oil is higher than that of animal oil (with very few exceptions).Since the source of dietary fat is mostly from fat-rich animal foods in addition to cooking, it is advisable to use vegetable oil as the main source of cooking oil to make the proportion of fatty acids appropriate.

Due to the high calorific value of animal fat, it is easy to eat and has a unique flavor.If the diet is balanced and prepared properly, and occasionally eat a small amount, it should be fine.Foreign nutrition scholars have proposed that the appropriate ratio of saturated, monounsaturated and polyunsaturated fatty acids in dietary oils is 1:1:1.Dietary cholesterol intake should be less than 300 mg per day.

Oil and Health

Cooking oil plays an important role in increasing the color, aroma and taste of food, and it is also one of the indispensable sources of nutrition for the human body.However, if eaten improperly, it can also have adverse effects or even harm to the body.

Unsaturated fatty acids contained in cooking oil are indispensable substances for the human body.And this kind of unsaturated fatty acid cannot be synthesized by itself in the human body and must be supplied by food.If the supply of unsaturated fatty acids is sufficient, the skin will be smooth and moist, and the hair will be black and shiny; if the body lacks unsaturated fatty acids, the skin will be rough, desquamated, and the hair will be brittle and easy to fall off.

(End of this chapter)