Complementary foods are not recommended for babies over four months old. Breastmilk is the most ideal food for infants, and exclusive breastfeeding can satisfy all the fluids, energy and nutrients needed by infants up to 6 months of age. In addition, breast milk is conducive to the establishment of a healthy micro-ecological environment in the intestinal tract and the maturation of intestinal function, reducing the risk of infectious diseases and allergies. Therefore, it is not recommended to add complementary foods for babies over 4 months old. In addition, the digestive system of 4-month-old babies is not yet well developed, and adding complementary foods too early may cause diarrhea in babies due to indigestion. It may also increase the risk of allergic diseases because of the inability to digest and absorb non-human proteins well. Therefore, it is recommended to supplement with infant formula when breastmilk cannot meet the growth and development needs of the baby. To summarize, it is not recommended to add complementary foods to babies over four months old.