Causes of constipation in one-year-old babies Constipation refers to the phenomenon that babies have difficulty defecating or have difficulty defecating. It is a common gastrointestinal problem. There are many reasons for constipation in one-year-old babies. Here are some possible reasons: Dietary problems. Unreasonable diet structure of babies is the main cause of constipation. If the baby only eats a single food for a long time, such as milk powder or pureed meals, it lacks dietary fiber and water, and the intestines cannot excrete smoothly, which will lead to constipation. Babies under one year old have relatively little activity, and lack of physical exercise is also one of the causes of constipation.