Food safety focus

Food safety focus

Food Safety Focus (December 29, 2008) – Food Safety Platform
Nutrients and Health: Energy and Protein
Food Safety Center
Risk communication group
Report by Ms. Feng Huizhong, Scientific Director

Starting from this issue, the nutrition series will focus on individual nutrients. First, we will introduce energy and protein. Energy is the driving force behind our daily activities, and protein is the substance that promotes our growth and development.


If the body is a machine, then food is fuel. To be more precise, carbohydrates, fats, and proteins in food provide energy for bodily functions and physical activity (see Table 1), but they can produce different energy values ​​(see Table 2). Each gram of fat produces more than twice as much energy as carbohydrates or protein. The body’s metabolism converts these three nutrients into energy and stores the excess energy in the form of fat. In other words, whether it is carbohydrates, protein or fat, if not consumed, it will be converted into fat stored in the body. When the body stores fatter, our weight will increase.

The amount of energy required varies from person to person and is influenced by a number of factors, including the food heat effect (the energy required to process the food), the basal metabolic rate, and the amount of physical activity. According to the recommended intake of nutrients in China, the energy needs of adult men and women with low physical activity are about 2400 kcal and 2100 kcal, respectively. In order to maintain weight, the energy we consume must be balanced with the energy we consume. Therefore, to control weight, we can reduce energy intake and/or increase the amount of activity.


The body uses protein to construct and repair all tissues. Amino acids are the basic building blocks of proteins. Nine of them are essential amino acids (see Table 3). The human body cannot synthesize itself or cannot synthesize enough quantities to meet the needs. Therefore, these nine essential amino acids are indispensable elements in our diet. In general, animal proteins are considered complete proteins because they contain all essential amino acids, while vegetable proteins (except soy protein) lack one or more essential amino acids, such as cereals lacking lysine, beans lacking methionine, and two They are all one of the nine essential amino acids. For those who strictly follow vegetarian diets, experts suggest that their diet should include foods of various vegetable origins so that different foods are not complementary enough (ie, one essential amino acid missing from a food source can also be provided by another food source). ), so that vegetarians can get all the essential amino acids from the diet even if they don’t eat meat.

Protein deficiency is not common in Hong Kong, but protein-energy malnutrition is one of the most prevalent malnutrition problems in the world and is widespread in Africa. At the other extreme, excessive protein intake does not bring additional health benefits because the extra protein that the body does not consume is converted to fat stored in the body. During the transformation process, the protein is broken down and excess nitrogen is excreted, increasing the burden on the liver and kidneys. Because patients with kidney disease need to pay special attention to this problem, they are generally advised to choose a high-quality protein but should limit protein intake.

According to the recommended intake of nutrients in China, adult males and females with low physical activity should eat 75 grams and 65 grams of protein per day. As for children, adolescents, pregnant women, and lactating women, more protein is needed to promote growth and development.

Meat, poultry, fish, eggs and dried beans provide a rich protein. According to the Healthy Eating Pyramid, these foods are located on the third floor of the pyramid, which should be “appropriately eaten.” In terms of actual weight, an adult should eat 5 to 6 (equivalent to 200 to 240 grams) of meat per day.

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