Fat (grease) and lipid-like substances (phospholipids, cholesterol, etc. ) is an important part of human tissues. Fat is mainly distributed around human skin tissue, omentum, mesentery and kidney. The content of body fat often changes with nutritional status, energy consumption and other factors. Fat is the concentrated energy source, and body fat is the "fuel warehouse" of human body, which can be used when necessary. The essential fatty acids provided are raw materials for synthesizing phospholipids and prostaglandins, which will cause skin dryness and desquamation, growth stagnation, reproductive dysfunction, hematuria and fatty liver when lacking. The highly unsaturated fatty acids contained in fish have the functions of lowering blood lipid, antithrombotic and improving brain function. Fat is also the carrier of fat-soluble vitamins (A, D, E, K), which can promote their absorption in the body. Fat in the diet can improve the flavor of food, stimulate appetite, stay in the stomach for a long time, and easily feel full.

The main physiological functions of fat are:

(1) constitutes human tissues. Phospholipids and cholesterol in fat are the main components of human cells, and they are the most abundant in brain cells and nerve cells. Some cholesterol is necessary for the production of steroid hormones in the body, such as adrenocortical hormone and sex hormone.

(2) supply heat energy. Fat contains more carbon and hydrogen than carbohydrates. Therefore, more heat can be released during the oxidation process. 1 g fat can release 9 kilocalories of heat energy and has the highest nutritional content.

(3) supply essential fatty acids. The essential fatty acids needed by human body are provided by food fat.

It is mainly used for the synthesis of phospholipids and is an important part of all cell structures. Maintaining the normal permeability of skin microvessels and its effects on sperm formation and prostaglandin synthesis are all important functions of essential fatty acids.

(4) Stimulate appetite and promote the absorption of some vitamins. Foods that contain no fat or little fat are not delicious. Fatty foods can increase 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, which is used to regulate body temperature, protect temperature-sensitive tissues and prevent heat loss. Fat distribution is filled in the gaps of internal organs, which can protect internal organs from vibration and mechanical damage and maintain the growth and development of skin.

(6) increase satiety. Fat stays in the stomach for a long time, which can increase satiety and make people less likely to feel hungry.

(7) As a solvent for fat-soluble vitamins, important vitamins such as vitamin A, vitamin D, vitamin E and vitamin K cannot be dissolved in water, and can only be absorbed by the human body if they are dissolved in lipid substances. For example, we often say that carrots are best not eaten raw, but fried with oil and meat, so that the vitamin A in carrots can be absorbed by the human body.