A very low-carbohydrate, high-fat diet may provide stronger metabolic benefits for people with obesity than a Mediterranean diet or a low-fat diet, according to a clinical trial published August 27 in the journal Cell Press. cellular metabolism. After four to five months of the ketogenic (or “Keto”) diet, about half of the participants with obesity and prediabetes no longer met the criteria for prediabetes.
“We know that weight loss can improve metabolic health in obese people,” says Samuel Klein, corresponding author of the study at Washington University School of Medicine in St. Louis, Missouri. “Our data suggest that if you have high liver fat and prediabetes, reducing carbohydrate intake may have important therapeutic effects on metabolism beyond simple weight loss.”
Comparison of three popular weight loss diets
It is estimated that 40% of adults in the United States are obese. Doctors often recommend low-fat, low-carbohydrate, or Mediterranean diets for weight loss, but researchers haven’t known whether one approach provides additional metabolic benefits beyond the effects of losing weight.
The three diets differ markedly in the amount of carbohydrates and fats they provide. A low-carb diet, also known as the Atkins or ketogenic diet, greatly restricts carbohydrates. In contrast, a low-fat diet can get up to 70% of its energy from carbohydrates. A Mediterranean diet emphasizes plant-based foods such as vegetables, olive oil, and nuts, along with moderate amounts of fish and dairy. A ketogenic diet can include foods high in saturated fats, including animal products.
To compare their effects, Klein and his colleagues enrolled 42 people with obesity, prediabetes, and fatty liver disease in a clinical trial. Participants were randomly assigned to follow a ketogenic diet, a Mediterranean diet, or a low-fat plant-based diet. All food was provided by the research team, and participants met with a dietician each week to help them follow their assigned meal plan.
Equivalent weight loss in all groups
The ketogenic diet provides only 4% of calories from carbohydrates and 73% from fat. In the Mediterranean group, 50% of calories came from carbohydrates and 35% from fat. The plant-based diet provided 70% of calories from carbohydrates and 15% from fat.
The researchers adjusted each person’s calorie intake so that participants in all three groups lost about 10% of their body weight. Reaching that goal took approximately four to five months.
At the end of the study, participants in each diet group had significantly reduced their body fat. Insulin sensitivity also improved in all three groups, helping the body control blood sugar more effectively.
Keto produced the largest drop in liver fat
Despite similar weight loss, the ketogenic diet produced the strongest changes in several measures of liver and metabolic health. Liver fat was reduced by an average of 67% among people following the ketogenic diet, compared to an average reduction of 45% in the Mediterranean and plant-based groups.
The researchers also tracked the participants’ metabolism over a 24-hour period by repeatedly analyzing their blood. People in the ketogenic group showed the greatest increase in glucagon, a hormone that helps reduce fat stored in the liver. They also had the largest decrease in blood insulin levels, another change that may help reduce liver fat, compared to participants who followed the other two diets.
“The most surprising finding was that participants in the ketogenic diet group did not experience an increase in blood fat or cholesterol levels despite consuming the most fat,” says Max Petersen, first author of the study from the University of Washington School of Medicine.
Prediabetes improved more in the Keto group
After the weight loss intervention, about 50% of participants who followed the ketogenic diet no longer met the criteria for prediabetes. That compares to 29% of those who follow the Mediterranean diet and 7% of those who follow the plant-based diet.
“GLP-1-based drugs have revolutionized obesity therapy. We now have a very effective pharmacotherapy to achieve significant weight loss,” says Petersen. “But in addition, our study shows that the specific composition of the diet can provide added benefits.”
The research was supported by the National Institutes of Health and the Barnes-Jewish Hospital Foundation.