The global prevalence of diabetes mellitus reached 382 million in 2013 and is expected to rise to 592 million by 2035. The consequences of diabetes mellitus, especially if it is poorly controlled, might be dramatic and lead to life-threatening conditions. Therefore, it is crucial to prevent diabetes mellitus, diagnose it as early as possible, and treat it effectively. In addition to medications, lifestyle modification − especially diet and eating habits − seems to be the instrumental factor in the management of diabetes mellitus. This review is focused on the benefits and risks of a low-carbohydrate diet in patients with type 1 and 2 diabetes mellitus. Clinical trials containing data on changes in metabolic parameters, such as fasting glucose, fasting insulin, and HbA_1c, resulting from the use of a low-carbohydrate diet by patients with diabetes mellitus were analyzed. Most of the included studies showed improvements in these parameters. Only one study reported an increase in HbA_1c, likely due to patients’ non-compliance with dietary instructions. Consequently, devoting time to clear explanations of dietary rules, providing help in implementing them, and further monitoring of patients’ food intake seem to be crucial. Although the outcomes of this study showed a beneficial effect of a low-carbohydrate diet on metabolic parameters, conducting further studies is still required to clearly and explicitly define all positive and promising outcomes of this review, as well as risks associated with the use of a low-carbohydrate diet by patients with diabetes mellitus.