One year old babies do not gain weight, the common causes are insufficient intake, poor digestion and absorption, increased consumption caused by disease, genetic factors, genetic metabolic diseases and so on. 1. Insufficient intake: Mostly seen in improper feeding, insufficient feeding, such as insufficient breast milk, but parents did not add complementary food in time, resulting in insufficient energy intake, or the child’s gastrointestinal function is weak, constipation and so on, leading to anorexia, causing insufficient energy intake. 2. Poor digestion and absorption: children due to gastrointestinal dysfunction, indigestion, food protein allergies and other triggers of diarrhea, resulting in poor intestinal digestion and absorption, nutrition can not be fully absorbed and utilized, resulting in weight gain. 3. Disease-induced increased consumption: such as repeated respiratory infections, congenital heart disease, tuberculosis infection, etc., resulting in increased body consumption. 4. Genetic factors: the parents themselves are thin, the baby is also thin. 5. Genetic metabolic diseases: such as hypothyroidism, phenylketonuria, etc., can also lead to weight loss. One-year-old baby weight does not increase, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.