Dietary Health Guide for Men: A Map of Food Nutritional Sources and In-Depth Analysis of Metabolism

Food Sources of Nutrients

(1) Carbohydrates: The main food sources of carbohydrates are plants, such as grains, beans, fruits, sugar, and the tubers and roots of vegetables.

(2) Fats: The main food sources of fat are the fat, bone marrow, and fatty meat of animals such as pigs, cattle, and sheep, dairy products, and egg yolks. The fats in dairy products and egg yolks are considered the best because they are easily digested and absorbed. The main sources of plant-based fats are sesame seeds, beans, peanuts, and nuts. Plant fats (vegetable oils) contain essential fatty acids and are considered ideal food fats.

(3) Proteins: The main sources of protein include lean meat, poultry, fish, shrimp, dairy products, and eggs. In addition, beans, bean products, nuts, and grains also contain protein. (4) Inorganic salts: Calcium and phosphorus mainly come from animal egg yolks, dairy products, dried shrimp, and plant-based foods such as soybeans, tofu, kelp, sesame paste, and leafy green vegetables. Sodium mainly comes from table salt and animal and plant-based foods. Zinc mainly comes from meat, poultry, seafood, eggs, dairy products, peanuts, and grains. Iron mainly comes from animal liver, egg yolks, and lean red meat. Plant-based foods such as red dates, brown sugar, and leafy green vegetables are also rich in iron. Copper mainly comes from mollusks and crustaceans, animal liver, and dairy products. Iodine mainly comes from kelp, seaweed, grains, walnuts, cocoa, and meat.

(5) Vitamins: Vitamin A comes from animal liver, milk, egg yolks, carrots, persimmons, spinach, and apricots. Vitamin D comes from egg yolks and cod liver oil. Vitamin B₁ comes from various whole grains, beans, animal organs, and lean meat. Vitamin C comes from fresh vegetables and citrus fruits, with fruits having the highest content. Folic acid comes from animal liver, leafy green vegetables, etc. Vitamin E comes from wheat germ, vegetable oil, leafy green vegetables, egg yolks, peanuts, etc.

(6) Water: The main food source of water is drinking water, with the remainder being the water contained in food and the water produced during the oxidation of food in the body.

Metabolism

The exchange of matter and energy between the human body and the external environment is called metabolism. Metabolism can be roughly divided into material metabolism and energy metabolism.

1. Material Metabolism

(1) Protein Metabolism: There are more than 100,000 kinds of proteins in the human body, and all these kinds of proteins are synthesized from 20 kinds of amino acids. These 20 kinds of amino acids are divided into two categories: one is essential amino acids, and the other is non-essential amino acids. Essential amino acids are amino acids that the human body cannot synthesize or synthesizes too slowly to meet the body's needs and must be provided by food. There are eight essential amino acids: leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Non-essential amino acids are those that the body can synthesize itself or convert from essential amino acids; they do not necessarily have to be obtained from the diet. Human proteins are synthesized from various amino acids in specific proportions; therefore, even a deficiency of just one essential amino acid can hinder the synthesis of that protein.

(2) Fat metabolism: After being digested and absorbed, dietary fat is mainly stored in the subcutaneous tissue and mesentery. When the body needs it, fat is broken down to release energy for use by tissue cells; its final products are carbon dioxide and water.

(3) Carbohydrate metabolism: Carbohydrates are classified according to their molecular structure into monosaccharides (such as glucose), disaccharides (such as sucrose), and polysaccharides (such as starch). The main carbohydrate in food is starch. Starch is a large polysaccharide composed of many glucose molecules. After digestion, the polysaccharide is hydrolyzed into glucose, which is absorbed into the body for energy supply. Under normal circumstances, about 70% of the energy consumed by the human body in various physiological activities comes from the breakdown of carbohydrates, and the final products of this breakdown are carbon dioxide and water.

(4) Water and Inorganic Salt Metabolism: Under normal circumstances, the intake and excretion of water and inorganic salts in the human body are balanced. Water in the human body is mainly excreted through the kidneys in urine, followed by excretion through sweat and respiration; inorganic salts in the body are also mainly excreted through the kidneys in urine or sweat.

2. Energy Metabolism

Food provides the human body with the energy necessary for various activities. Among various food components, protein, carbohydrates, and fats are particularly rich in energy. For example, the average energy content of each gram of protein is 4.1 kcal (the heat required to raise the temperature of 1 liter of water by 1°C is 1 kcal, 1 kcal = 4.184 kJ), the average energy content of each gram of carbohydrate is 4.1 kcal, and the average energy content of each gram of fat is 9.3 kcal. Thus, the caloric value of protein is 4.1 kcal, carbohydrates are 4.1 kcal, and fat is 9.3 kcal.

Basal Metabolism

Basal metabolism refers to the metabolic processes that maintain body temperature and the physiological activities of the nervous, circulatory, and respiratory systems under conditions such as wakefulness, rest, fasting, and a room temperature of around 20°C. A person's basal metabolic rate varies with age, sex, height, and weight.

People engage in various activities throughout the day, such as learning, working, and exercising. Therefore, the energy consumed by the human body in a 24-hour period is necessarily higher than the energy consumed by basal metabolism. Generally speaking, the greater the intensity of physical labor, the more energy is consumed, and the more calories are supplied by food. Adolescents, both boys and girls, are in a period of growth and development, with high activity levels and vigorous metabolism. Therefore, it is important to pay attention to nutritional supplementation, especially protein intake. This is because, on the one hand, the protein components in adolescents' bodies need to be renewed; on the other hand, they need to use protein and other materials as the main building blocks to generate more new cells than adults to meet the needs of their growth and development. Therefore, adolescents should consume more protein daily than adults.