The three major nutrients of the human body

The three major nutrients for the human body refer to carbohydrates, fats and proteins. These three nutrients are essential nutrients for the body and can be obtained from food. The carbohydrate, protein and fat content in the human body can also directly judge the health of the body, because such substances will also affect health.

The three major nutrients refer to carbohydrates, fats and proteins, which are nutrients for humans and animals. All three types of substances can be obtained from food, but are not stored in the same body organs.

Interrelationship

The relationship between carbohydrate metabolism and lipid metabolism

It should be clear that the conversion between carbohydrates and fats is bidirectional, but the degree of conversion between them is different. Carbohydrates can form fats in large quantities. For example, when yeast is cultured in a sugar-containing culture medium, lipids can be produced in the cells. The fat synthesized by some types of yeast can be as high as 40% of the dry weight of the yeast. However, fats cannot be converted into carbohydrates in large quantities. For example, when some animals hibernate, fats can be converted into carbohydrates.

The relationship between carbohydrate metabolism and protein metabolism

First of all, we need to clarify the concepts of essential amino acids and non-essential amino acids: the so-called non-essential amino acids refer to amino acids that can be synthesized in human cells; the so-called essential amino acids refer to amino acids that cannot be synthesized in human cells, or the synthesis rate cannot meet the needs of the human body and must be obtained from food. There are 8 essential amino acids for the human body, namely lysine, tryptophan, phenylalanine, leucine, isoleucine, threonine, methionine and valine.

The conversion between carbohydrates and proteins can also be bidirectional: the intermediate products of carbohydrate metabolism can be converted into non-essential amino acids, but carbohydrates cannot be converted into essential amino acids, so the process of carbohydrate conversion to protein is not comprehensive; however, almost all natural amino acids that make up protein can be converted into carbohydrates after deamination, and the nitrogen-free part produced can be converted into carbohydrates. For example, dogs with artificial diabetes fed with protein can have more than 50% of their food protein converted into glucose.

The relationship between protein metabolism and lipid metabolism

The conversion between protein and lipids varies depending on different organisms. For example, it is not easy for humans and animals to use fat to synthesize amino acids, but plants and microorganisms can produce amino acids from fatty acids and nitrogen sources. Some amino acids can also be converted into glycerol and fatty acids through different pathways. For example, if animals are fed with food containing only protein, they can also store fat in their bodies.

The metabolism of carbohydrates, proteins and lipids is mutually restricted

Carbohydrates can be converted into fats in large quantities, but fats cannot be converted into carbohydrates in large quantities. Only when carbohydrate metabolism is impaired will fat and protein be used to supply energy. When carbohydrate and fat intake are insufficient, protein decomposition will increase. For example, when the sugar metabolism of diabetic patients is impaired, fat and protein are used to break down the sugar, so the patients appear emaciated.