Prepackaged foods refers to foods prepackaged or made with packaging materials and containers, including foods prepackaged with packaging materials and capacities and with uniform quality or volume labels within certain limits, including biscuits, bread, soy sauce and dairy products. The General Rules for Nutrition Labeling in prepackaged foods stipulates that prepackaged foods should indicate the contents of four nutrients and energy ("4+ 1") and their percentages in nutrient reference values, where "4" refers to core nutrients, namely protein, fat, carbohydrate and sodium, and "1" refers to energy.

The main purpose of formulating the Measures for the Administration of Nutrition Labels is to guide and standardize the labeling of food nutrition labels in enterprises, guide consumers to choose foods reasonably, promote dietary nutrition balance and protect people's health. At present, people have attached great importance to health care, but few people know how to quantify the nutrients they need to eat every day. In fact, it is very beneficial for health to know the nutrition label and use it to choose food. Many chronic diseases are eaten. First, the unreasonable diet structure leads to unbalanced nutrition, which leads to chronic diseases such as diabetes and cardiovascular diseases over time.

The food nutrition label is the source for consumers to know the nutritional components and characteristics of prepackaged foods, and it is also the basis for their health needs to choose food. It is also a means for consumers to protect their informed rights and interests, and it can also guide enterprises to produce more foods that meet nutritional requirements. Then, since it is an important guide for consumers to buy food, how should consumers make a reasonable choice of food by using nutrition labels?

We must first calculate the energy we need in a day. Dietary energy mainly comes from carbohydrate, fat and protein in food, so these three nutrients are also called thermogenic nutrients (heat sources). In vivo, the capacity of 1g carbohydrate is 4 kcal, that of 1g fat is 9 kcal, and that of 1g protein is 4 kcal. These three high-capacity nutrients have their own special functions in the body and can influence each other, so the energy supply ratio should be appropriate. According to the dietary habits of China people, carbohydrates account for 55%-65% of the total energy, fat accounts for 20%-25% of the total energy, and protein accounts for 10%- 15% of the total energy. Energy demand is classified according to labor intensity: resting state is 25-30 kcal/kg, light physical strength is 30-35 kcal/kg, medium physical strength is 35-40 kcal/kg, and heavy physical strength is 40-45 kcal/kg.