Low urea indicates that the body produces less nitrogenous metabolic waste, which can occur in the following situations: First, young children, especially those who are picky eaters and those who are yellow and lean, generally have lower than normal urea, and it is recommended to actively enhance nutrition by eating meat, eggs and milk daily to supplement the essential amino acids needed by the human body. Second, women who lose weight and their young men, because of the need to actively control energy intake during weight loss, if the essential amino acids required by the human body are not replenished in a timely manner, low urea will occur. Third, the intake is normal, but the body consumes more state, such as advanced tumor patients, cachexia patients, urea will be lower than normal.