The fever is a state of negative nitrogen balance, when the body catabolism increases and anabolism decreases, the three major metabolic substances (protein, fat, sugar) are in a state of massive decomposition and consumption, because the body temperature is in a continuous rise will consume excessive energy and calories, when the intake is not enough will produce wasting. 2, still in the fever will make bacteria, viruses, fungi, pathogens, microorganisms, sources of infection, etc. in the body release and decomposition, The release and decomposition of bacteria, viruses, fungi, pathogens, microorganisms, and infection sources in the body, especially when the release of inflammatory factors in the body will increase the body temperature, the body will increase heat production, which will consume a lot of calories and heat energy, so the body will be thin when fever is present. 3. The appetite of people when fever is usually bad, digestion and absorption function will be weakened, so the intake of heat energy can not be absorbed by the body in time, so the fever will Therefore, the heat intake cannot be absorbed by the body in time, so the body will lose weight when fever is present.