Diabetic patients after a low carbon diet, the body may not have enough sources of sugar, the body will be through the gluconeogenesis to raise blood sugar, then there may be a fasting blood glucose increase. In addition, high fasting blood glucose in diabetic patients after a low carb diet may also be caused by the improper use of hypoglycemic drugs and the dawn phenomenon. A low-carbon diet (low-carbohydrate diet) is a diet that meets the five major nutrients of protein, vitamins, minerals, dietary fiber, and water, while moderately reducing the intake of fats and carbohydrates by 30% to 50% of the normal free-feeding energy. The half-life of hypoglycemic drugs used by some diabetic patients is short and not enough to maintain normal blood glucose level for a long period of time, so the phenomenon of high fasting blood glucose may occur. The dawn phenomenon, i.e., good glycemic control at night and no hypoglycemia occurs, only transient hyperglycemia occurs at dawn, which may be due to excessive secretion of free cortisol, growth hormone, etc. in the early morning. It is recommended that patients with elevated fasting blood glucose after a low-carbon diet should consult their doctors in a timely manner, and take targeted treatment under the doctors’ guidance, and do not blindly take other measures, so as to avoid delaying the condition and triggering adverse consequences.