First, improper feeding, insufficient long-term food intake, such as insufficient breast milk, failure to add complementary food as early as possible, and the quality and quantity of artificially fed food failed to meet the needs, such as excessive dilution of milk or simple feeding with starchy food, sudden weaning, and infants unable to adapt to new foods.

Second, poor eating habits. Irregular diet, partial eclipse, nervous vomiting, etc.

Third, the disease factor. Diseases affect food, hinder the digestion, absorption and utilization of food and increase the consumption of the body. Common diseases that easily lead to malnutrition include congenital infantile diarrhea, chronic enteritis and intestinal parasitic diseases, tuberculosis, measles, recurrent respiratory tract infections, chronic urinary tract infections and so on. Some congenital malformations of digestive tract and severe congenital heart disease will cause feeding difficulties. Some hereditary metabolic disorders and immunodeficiency diseases will also affect the digestion, absorption and utilization of food.