Foods can provide the necessary nutrients for the human body to satisfy the physical demands. However, the nutritional value of the foods can be seriously decreased by four elements in everyday life. These four elements include toxic metal, , pesticide and free radical. These pollutants can not only destroy the nutrients contained in foods, but also affect the absorption of the nutrients inside the human body. In order to protect the nutrients in the foods, people should try their best to reduce the pollutants. 

The toxic metal mainly includes lead, aluminium, cadmium, copper and mercury. These toxic metals can enter the human body through air, food, and food packaging. Some skills should be used to prevent the harms caused by toxic metals. For example, people can use the mixture of water and vinegar to clean vegetables and fruits. The pot made of aluminium should be abandoned. In addition, people should increase the intake of the foods containing vitamin C, calcium and zinc to resist the danger of these toxic metals. People can choose fresh vegetables, fruits and nuts. The intake of wine should be decreased, as alcohol can accelerate the absorption of lead inside the human body.

Nitrate can be integrated with amine to form nitrosamine after it enters the human body. The nitrosamine can probably cause cancer. Nitrate usually exists in smoke-dried meat, unstrained water and so on. Therefore, it is necessary for people to reduce the intake of smoke-dried foods and clean their teeth frequently. Water must be strained before people drink it.

Pesticide can seriously affect the nutritional value of vegetables, fruits and grains. What's more, the health of animals can also be affected. That is to say, the foods needed by people can be polluted by the pesticide. Once people eat the foods containing pesticide, the physical health can also be seriously threatened. People should eat the organic fruits and vegetables as far as possible. In addition, vitamins like vitamin A and mineral substances like selenium should be supplemented.

Free radical can destroy the cells inside the human body to produce more free radicals and cause various problems. The harms of free radicals can be decreased by stopping smoking and decreasing the intake of fried foods. What's more, people should supplement the nutrients which can resist the oxidation, such as vitamin A, vitamin E, zinc and selenium. People can also take deep breath to send oxygen to the cells to resist free radicals.