Core Tip: Why is it necessary to ensure adequate fat content in the diet? To provide the body with energy and essential fatty acids, promote the absorption of fat-soluble vitamins, improve food flavor, and increase satiety.
In recent years, due to the increasing trend in the incidence and mortality of chronic diseases (such as cardiovascular diseases, tumors, and cancer), people often have a prejudice against fat, and some even develop a fear of it; they consume only plant oils and avoid animal oils, and lack a correct understanding of the functions and metabolism of lipids. Lipids are an indispensable class of nutrients for the human body and have important physiological functions.
As the saying goes, "Food is the first necessity of the people." This illustrates that food is an essential material basis for human life activities. The nutritional value of food depends on the quantity, type, quality, and availability (digestion and absorption rate) of the nutrients it contains. A complete diet should include all the essential nutrients for the human body in appropriate proportions, which is what we often refer to as a "balanced diet."
The oils and fats we refer to in our daily lives contain two substances: neutral fat (triglycerides) and lipids (phospholipids, sterols, etc.). In the human body, lipids consist of 95% triglycerides and 5% other lipids, which we collectively call fat. In our diet, there is a wide variety of lipids, the vast majority of which are neutral fats. Like carbohydrates, fat's primary function in the body is to provide energy. Under normal conditions, 20% to 30% of the energy in the diet comes from fat. An adult of moderate intensity needs 1 to 2 grams of fat per kilogram of body weight daily.
Fats are the nutrient with the highest caloric content in the diet. They contain more potential energy per unit weight than protein and carbohydrates. In terms of weight and volume, they are the most economical food source. Furthermore, when they burn (or are oxidized), they release a large amount of water, which is of great significance in the metabolic reactions of an organism.
Why is it necessary to ensure adequate fat content in the diet? It is because fats have important physiological functions for the human body. In terms of nutrition, the main functions are as follows:
1. Fats provide energy for the body and are the body's main energy source. 1 gram of fat burned in the body can produce 37.7 kJ (9 kcal) of energy, while 1 gram of protein or 1 gram of carbohydrate can only produce 16.7 kJ (4 kcal) of energy. If the human body lacks fat for a long time, it can lead to insufficient energy, weight loss, and even the loss of work or labor capacity. Because infants have a smaller stomach capacity but need more energy than adults, the supply of fat in their diet is particularly important. For example, the fat in breast milk provides 50% of the required energy.
2. Fats provide essential fatty acids. Essential fatty acids are those that the human body cannot synthesize and must be obtained from food fats, such as linoleic acid (C18:2, octadecadienoic acid) and linolenic acid (C18:3, octadecatrienoic acid), which have special physiological functions for the human body. They are components of cells and tissues, help maintain the integrity of the skin, mucous membranes, and capillaries, participate in the synthesis of prostaglandins, and promote cholesterol metabolism. A long-term deficiency in the diet can cause significant harm to human health.
3. Fats promote the absorption of fat-soluble vitamins. Vitamins A, D, E, K, and carotene (provitamin A) are insoluble in water and can only be dissolved in fat, hence they are called fat-soluble vitamins. Dietary fat acts as a solvent for fat-soluble vitamins, promoting their absorption and utilization. Some fats themselves contain fat-soluble vitamins, such as vitamin E in vegetable oils, and vitamins A and D in butter and cod liver oil.
4. Fats can improve food flavor, enhance the sensory properties of food, and increase people's appetite. Any natural oil has its own unique taste. A well-prepared dish often varies in color and flavor depending on the oil used.
5. The satiating effect is another function of fats. It prolongs the digestive process of food in the body and prevents premature hunger after eating.
In addition, fats also have functions such as maintaining body temperature and protecting internal organs. Fat in the human body is distributed under the skin and around the internal organs, acting as a heat pad and a protective pad. Fat is a poor conductor of heat and prevents excessive loss of body heat, thereby maintaining a constant body temperature. Adipose tissue, which is mainly composed of liquid fat, is elastic and taut, acting like a soft pad to separate the various organs in the body, preventing them from pressing against each other, and at the same time providing a buffer against mechanical impacts, thus protecting the internal organs and muscles from injury.
In addition to neutral fats, the lipids and fat-associated substances contained in them are also very important for human health. Lipids include phospholipids and sterols, and their main function is as a basic component of cell membranes (accounting for about 50% of the membrane weight), including cell membranes and various organelle membranes, and they also constitute some important active substances in the body.
Thus, it is clear that dietary fat is an indispensable substance for the human body.
However, if excessive fat is consumed over a long period, it can cause indigestion, loss of appetite, diarrhea, and other issues. Excessive animal fats, in particular, can lead to obesity, hyperlipidemia, and coronary heart disease, causing great harm to human health.
So, how much fat should we actually consume in a day?
The "Dietary Guidelines for Chinese Residents" recommends: Based on the fact that the dietary fat of Chinese residents mainly comes from animal foods, beans, nuts, and cooking oil, only by controlling cooking oil to no more than 25 or 30 grams per day can the basic requirement of a reasonable diet be met, where fat provides 25% to 30% of the dietary energy. If the intake of animal fat in the diet is low, the amount of cooking oil can be appropriately increased.