Nutrition therapy is the cornerstone in the management of prediabetes and diabetes mellitus. The diet should aim to improve glycemic control and cardiovascular risk factors and to prevent hypoglycemia. There is no specific diet for diabetes mellitus. Food choices should be based on individual preference, culture, and availability. The pleasure of eating should be kept in mind to ensure long-term adherence. Medical nutrition therapy should ideally be provided by a registered dietician-nutritionist. A proper meal plan encompasses not only quantity but also quality and eating patterns. For diabetes mellitus, the recommendation is to consume food rich in dietary fibers and avoid food containing sugar, salt, and saturated fat. Meals should be spaced evenly throughout the day. Day-to-day meals should be consistent. The key to nutrition therapy in gestational diabetes mellitus is the consumption of small to medium-size meals distributed throughout the day to maintain normoglycemia and avoid ketosis or hypoglycemia. The diet should be modified on the basis of the presence of comorbidities. Patients with cardiovascular disease should avoid processed food rich in salt and saturated fat. In the case of obesity, the emphasis should be on calorie restriction rather than nutritional composition. Patients with chronic kidney disease do not need to restrict their protein intake. Overall, diet should be palatable and based on scientific facts.