People with type 2 diabetes or even prediabetes are most often treated first with diets that reduce carbohydrate intake. But the question, “How low should you go?” persists. There is plenty of controversy surrounding that question of carb intake, and at the moment there isn’t a lot of research to help patients and physicians find an answer.

When you have diabetes, the body has lost the ability to control blood sugar levels, and what affects your blood glucose is what you eat.

Most people get about half of their daily calories from carbohydrates. This is not necessarily a bad thing — until one considers that for so many diabetics, roughly 80 percent of those calories come in the form of refined carbs and added sugars found in foods like soft drinks, candy, bread, baked goods and pizza crust. And that is definitely not good.

Does a ketogenic diet offer any health benefits over the Mediterranean diet?

To see what kind of diet works best for diabetes management and which is easiest for most people to stick with, Stanford University researchers compared two low-carb diets, the keto diet and the Mediterranean diet.

Does a ketogenic diet offer any health benefits over the Mediterranean diet? To find an answer they put the two diets in a head-to-head study to compare how each affected blood glucose, cardiometabolic risk factors, weight loss, nutrition, and how easy each was to stick with.

Thirty-three adults with type 2 diabetes or prediabetes participated in the one-year study. Half of the people in the study followed the ketogenic diet for 12 weeks, and the other half followed the Mediterranean diet. At the end of 12 weeks, the groups switched to the other low-carb diet and followed it for 12 weeks.

Participants on both diets were asked to eat lots of non-starchy vegetables and avoid refined grains, as well as food or drinks with added sugars.

While on the keto diet, participants limited their carb intake to 20 to 50 grams/day, about 80 percent lower than usual, and they limited their protein intake to 1.5 grams of their ideal body weight per day. They were allowed to eat as much fat as they wanted, and asked to eat at least three servings of non-starchy vegetables every day.

The Mediterranean diet consisted of mostly plant foods like fruit, vegetables, legumes, whole grains, nuts and seeds in addition to fish for protein and olive oil for fat. There was no set parameters for nutrient intake.

During the first four weeks of the study, the participants were sent packaged meals to increase adherence to the diets. Over the last eight weeks, people were allowed to choose and prepare their own food. This gave researchers an insight into how realistic it was for people to follow the diets.

Both diets improved blood glucose control in the participants with similar decreases in HbA1c levels, an indicator of long-term blood sugar values. Other clinical benefits noted were improvements in fasting insulin, glucose levels, HDL (good) cholesterol and ALT, a liver enzyme. Weight loss was similar on both diets.

Participants on both diets were asked to eat lots of non-starchy vegetables and avoid refined grains and food or drinks with added sugars.

Though the participants did a pretty good job of limiting added sugar and refined grains, the keto diet was felt to be too restrictive by many people. When the researchers checked with the participants three months after the study ended, the Mediterranean diet seemed to be the one most people were following, and those eating it had maintained their lower blood glucose numbers and weight loss.

The American Diabetes Association (ADA) recommends a low-carb diet to prevent or manage diabetes as long as the diet includes plenty of non-starchy vegetables like leafy green vegetables, green beans, carrots and cabbage, and discourages the use of refined grains and added sugars.

The keto diet is considered an ultra-low-carb diet that is high in fat and severely restricts carbohydrates, while the Mediterranean diet is low in carbs, moderately high in fat and puts an emphasis on eating plant foods — fruits, vegetables, legumes, whole grains — as well as olive oil and fish.

While the keto diet falls within the ADA’s criteria, the consequences concern nutrition experts because the fewer carbs a person eats, the more food groups are left off the table and the less fiber a person consumes. With a ketogenic diet, foods like legumes, fruits and whole grains are sacrificed for foods high in protein and fat.

There were are no additional benefits from eating the ultra-low-carb keto diet for people with diabetes and prediabetes, according to this study. The Mediterranean diet was considered less restrictive and worked as well as the keto diet in controlling blood glucose. It also appeared easier to sustain for those with diabetes — another plus for the Mediterranean diet.

The study was published in the American Journal of Clinical Nutrition.