The Potential Impact of Low-Carb Diets on Prediabetes: Insights from a Clinical Trial

Prediabetes, a condition marked by higher-than-normal blood sugar levels, puts individuals at a heightened risk for developing diabetes. This condition affects an estimated 96 million American adults, necessitating effective prevention strategies. According to a clinical trial published in JAMA Network Open, a low-carb diet might be a practical approach for individuals with prediabetes to restore their blood sugar levels to healthier levels.

The study, adhering to a randomised clinical trial design, enrolled 150 overweight older adults with untreated prediabetes or less severe diabetes, with an average body mass index (BMI) of 35. The group consisted of 74% women and was 59% Black. Half of the participants were assigned a low-carb diet with regular dietary counseling, while the other half continued their usual diet.

For the initial three months, participants in the low-carb group were instructed to limit carbohydrate intake to below 40 grams per day, equivalent to an English muffin and an apple’s worth of carbs. In the subsequent three months, the carb limit was increased to 60 grams per day. The diet emphasized proteins and healthy fats, recommending foods like non-starchy vegetables, fish, poultry, lean meat, eggs, olive oil, avocados, nuts, seeds, Greek yogurt, low-carb milk, and modest amounts of cheese.

Results obtained from blood testing after three and six months revealed noteworthy improvements in the low-carb group, including a greater reduction in A1C and fasting blood glucose levels and an average weight loss of 13 pounds. These modest improvements in A1C levels corresponded to a nearly 60% decreased risk of developing diabetes within the next three years.

However, it’s crucial to point out the variations in A1C reduction across races. White participants had a more significant decrease than Black participants, implying that the response to a low-carb diet might not be uniformly effective across different racial groups.

The study also raised questions about the extent of the contribution of the weight loss to improved blood sugar control. A low-carb diet can directly improve blood glucose levels by reducing appetite and lessening the pancreas’s burden to produce insulin. But it’s uncertain if these effects are the leading contributors or if the weight loss plays a substantial role.

Despite promising results, the study had several limitations, such as the intensive dietary counseling provided to the low-carb group and self-reporting of daily diets. Furthermore, the study’s six-month duration doesn’t provide insights into the long-term sustainability of a low-carb diet.

Additionally, the feasibility of the rigorous low-carb diet approach adopted in the study in everyday life has been questioned. While the carb limit of 40–60 grams per day is lower than the recommended daily intake of 225–325 grams, it remains to be seen if similar results can be obtained with a less restrictive low-carb diet.

Concerns also linger about the potential long-term impacts of low-carb diets on overall health, with some studies suggesting they may elevate the risk of heart disease, kidney problems, and osteoporosis. Conversely, others have found beneficial effects on blood pressure, cholesterol levels, and heart disease risk factors. More research is necessary to fully understand these potential risks and benefits.

To summarize, while the study suggests that a low-carb diet may effectively improve blood glucose levels and induce weight loss in individuals with prediabetes, its long-term sustainability and suitability for all individuals remain uncertain. Consequently, it’s essential for prediabetes patients to collaborate with healthcare providers to determine a healthy eating pattern tailored to their needs, considering the potential risks and benefits of any dietary changes.