Being thinner and thinner day by day may be caused by improper diet, or it may be caused by diabetes, malignant tumors and other diseases. 1. Improper diet: too low calorie intake, especially protein intake is insufficient, easy to cause protein malnutrition, usually occurs in picky eaters, partiality and other people. It can be improved by adopting a high-calorie, high-protein diet and actively exercising at the same time. 2. Diabetes mellitus: manifested as polydipsia, polyphagia, polyuria, and weight loss, and in the later stage, there may be multiple organ function damage, such as diabetic nephropathy, diabetic ophthalmopathy and so on. 3. malignant tumors: early part of the malignant tumors manifested as weight loss, no obvious other symptoms. 40 years of age after the crowd, especially with a family history of cancer, if a sudden weight loss, need to be vigilant about this kind of disease. In summary, day by day thin, excluding dietary factors, need to consider diabetes, malignant tumors and other disease factors. If necessary, it is recommended to consult a doctor in time to avoid delaying the condition.