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When you consume foods or drinks containing carbohydrates, such as sugars, fibers, and starches, your body breaks them down into glucose, a type of sugar, and raises the levels of glucose in your blood. In response to increasing glucose levels in the blood, the pancreas releases insulin to facilitate the update of glucose into the cells. This tightly regulated mechanism keeps glucose levels in the blood at a constant, low ratee, while your body can use the sugar as energy.

In patients with diabetes, the mechanism of glucose uptake doesn’t work properly, and blood glucose levels rise abnormally whenever the body is exposed to sugary foods. In type I diabetes the pancreas cannot produce enough insulin to accomplish the task of glucose uptake into the cell. In type II diabetes, the cells that are the target of the insulin, no longer respond to the hormone and glucose cannot be moved from the blood into the cell. This leads to a situation when both insulin and blood glucose levels are elevated (Get smart on Carbs, American Diabetes Association).

Low carb diets are generally recommended for those who have Type II diabetes or those who are at risk of developing the disease due to their inability to manage their blood glucose. This kind of dysregulation is largely impacted by diet. The American Diabetes Association recommends a low-carb diet to manage or prevent diabetes. The goal of this low-carb diet is to minimize the intake of added sugars and refined grains, and to include non-starchy vegetables and other nutrient-dense carbs. Although low carb diets are a widely agreed upon treatment method for patients with diabetes because of their benefit in controlling blood glucose levels and aiding in weight loss, there isn’t much research on the specifics of how much and which types of carbs to restrict.

Two of the most popular low carb diets include the Ketogenic and Mediterranean diets. While both diets are low in carbs, the Keto diet is more restrictive of carbs and very high in fat (mainly coming from animal sources) while the Mediterranean diet is only moderately high in fat (mainly coming from plant-based sources) and includes much more vegetables, legumes, fruits, whole grains, olive oil, and fish.

In a recent clinical trial from Stanford University, the investigators compared the effects of the Keto and Mediterranean diets on blood glucose, cardiovascular risk factors, weight loss and nutrition, as well as how easily participants were able to adhere to their prescribed diet in their daily lives. The study was conducted from June 2019 to December 2020, Gardner and his team of researchers recruited 40 adults with Type II diabetes or prediabetes and split them two groups, one group starting with one diet and switching to the other after a 12-week period. This crossover design allowed participants to act as their own controls (Gardner et al., 2022).

During the Ketogenic diet, participants were advised to limit carbs by about 80% less than usual, and proteins to up to 1.5 grams per kilogram of their ideal body weight per day and to consume as much fats as they wanted. In the Mediterranean diet phase, participants were told to adhere to a mostly plant-based diet that included legumes, fruits, vegetables, whole grains, nuts, seeds, as well as fish as a protein source and olive oil for fat. Both diets encouraged consuming high quantities of vegetables and avoiding added sugars and refined grains as much as possible.

As the popularity of the Keto diet has grown significantly in the past few years, even for those not at risk for diabetes, it has raised concerns from several nutritionists about the extreme restrictions required to follow the Keto diet which does not allow legumes, fruits, and whole grains. Christopher Gardner, the director of nutrition at the Stanford Prevention Research Center and lead researcher on the study, is one of those concerned experts and said, “The lower in carbs you go, the more you’re wiping out entire food groups that are considered very nutrient dense and healthy. What is it about this diet that would be so compelling that you would give up some of those central tenets of health and nutrition?” (Gardner et al., 2022) Gardner’s main question throughout the study was to find out whether the elimination of legumes, fruits and whole grains in the keto diet offered supplemental health benefits for struggling with diabetes.

After collecting blood samples at various points throughout the study, researchers found that both diets improved blood glucose control (shown through drops in HbA1c levels), showed similar effects on weight loss, and showed improvements in fasting insulin and glucose, HDL cholesterol, and the liver enzyme ALT. The two statistically significant differences between diets were seen in a decreased LDL cholesterol level with the Mediterranean diet versus keto and a more significant decrease in triglycerides on the keto diet (although both diets caused a decrease). Regarding nutrients, the Mediterranean diet provided more fiber, thiamin; vitamins B6, C, D, and E; and phosphorus while the keto diet provided more vitamin B12 (Gardner et al., 2022).

In terms of sticking to the diets in the real world, the research team found that three months after the trial most participants were eating closer to a Mediterranean diet than Keto when left to their own accord. Even participants who had followed the Keto diet nearly perfectly during the trial had largely strayed from it after the trial had ended due to its highly restrictive barriers.

The reseearchers’ main takeaway from the trial is that there were no additional health benefits from eliminating legumes, whole grains, and fruits to successfully follow a low-carb diet. For those at risk for or who have diabetes, the less restrictive Mediterranean diet was just as effective at controlling blood glucose levels and lowering HDL cholesterol while being the more sustainable diet to adhere to for extended periods of time. The most important part of both low-carb diets was to limit added sugars and refined grains and include an abundance of vegetables. Beyond that, Gardner said, “there’s no reason to restrict heart-healthy, quality carbohydrate foods above and beyond. (Gardner et al., 2022).

This study emphasized the importance of including a wide variety of whole foods into your daily diet in order to receive enough vitamins and nutrients for overall health. Especially for those not struggling to maintain control over their blood glucose levels, there is no need to cut out complete food groups when eating a diverse assortment of nuts, seeds, legumes, fruits, vegetables, and whole grains is the best way to ensure you’re getting all the nutritional benefits a healthy diet can offer.