“The lower in carbs you go, the more you’re wiping out entire food groups that are considered very nutrient dense and healthy,” he said, noting that to achieve an extreme restriction of carbohydrates, the ketogenic diet prohibits legumes, fruits and whole grains. “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?”
Eating for science
In the new study, conducted from June 2019 to December 2020, Gardner and his team recruited 40 adults with Type 2 diabetes or prediabetes to try both the ketogenic diet and the Mediterranean diet. Half the participants started with the ketogenic diet, and the other half with the Mediterranean diet. After 12 weeks, the groups switched and tried the other diet for 12 weeks. This crossover design allowed participants to act as their own controls.
In the ketogenic diet phase, participants followed a version known as the well-formulated ketogenic diet. They were advised to limit carbs to 20-50 grams/day (about 80% less than usual) and proteins to 1.5 grams per kilogram of their ideal body weight per day, and to consume as much as they wanted in fats. They were asked to consume at least three servings of non-starchy vegetables a day.
In the Mediterranean diet phase, participants were advised to follow a mostly plant-based diet that included vegetables, legumes, fruits, whole grains, nuts and seeds, as well as fish for animal protein and olive oil for fat.
Both diets encouraged eating lots of vegetables and eliminating added sugars and refined grains as much as possible. The main question, Gardner said, was whether the keto diet offered additional health benefits from eliminating legumes, fruits and whole grains.
To set the participants up for success, the study sent ready-to-eat food to both groups during the first four weeks of each diet through the food delivery service Methodology. Short of feeding people all their meals in a lab, this approach was the best way to maximize adherence to the diets, Gardner said.
For the remaining eight weeks, participants were responsible for choosing and preparing their own food, giving researchers…