Despite the numerous groups of hypoglycaemic drugs available, disability and mortality from complications of diabetes mellitus (DM) are increasing every year. This requires new effective approaches to the management of patients with DM. One of these approaches is diet therapy. Diet is considered the most important component of DM treatment by all authoritative organisations. Before the discovery of insulin, carbohydrate-restricted diets were widely used for DМ, but recently, leading publications have reported that dietary correction with carbohydrate restriction is required without clear guidelines on the extent of such restriction, and the focus is mainly on drug treatment. Analysis of the literature confirms the positive effect of low-carbohydrate diets (LCD) on weight loss, improvement of the glycaemic profile in DМ, and reducing the number and doses of hypoglycaemic drugs, but it remains unclear which diet to choose in a certain situation, which one will give the best results and be safe in the short and long term. Studies on this issue have been conducted, but their results are contradictory. To date, there is no consensus on which LCD diet is the optimal solution for DМ. The article describes a clinical case of four months treatment of LCD with moderate carbohydrate intake and its effect on weight, metabolic parameters, and hypoglycaemic therapy in a patient with long-term DM, corrected with insulin therapy for the last 10 years. This diet, combined with the patient’s high compliance, led to an 11-kilogram weight loss, improved carbohydrate metabolism and withdrawal from insulin therapy, as well as helped normalise blood pressure without the treatment of antihypertensive drugs and improved kidney function.