Keto Diet Slashed Liver Fat by 67% in Clinical Trial

A very low-carbohydrate, high-fat diet may offer stronger metabolic benefits for people with obesity than a Mediterranean diet or a low-fat diet, according to a randomized clinical trial published August 27 in the Cell Press journal Cell Metabolism. After four to five months on a ketogenic, or "keto," diet, about half of participants with obesity and prediabetes — blood sugar higher than normal but not yet at diabetic levels — no longer met the criteria for prediabetes. An estimated 40% of adults in the United States have obesity.

"We know weight loss can improve metabolic health in people who are obese," said Samuel Klein, the study's corresponding author at Washington University School of Medicine in St. Louis, Missouri. "Our data suggest that if you have high liver fat content and prediabetes, reducing carbohydrate intake can have important therapeutic effects on metabolism beyond just weight loss alone."

Klein and colleagues enrolled 42 people with obesity, prediabetes, and fatty liver disease, randomly assigning them to a ketogenic, Mediterranean, or low-fat, plant-forward diet, with all food supplied and weekly dietitian visits. The keto diet drew 4% of calories from carbohydrates and 73% from fat; the Mediterranean diet, 50% carbohydrates and 35% fat; the plant-forward diet, 70% carbohydrates and 15% fat. Calories were adjusted so each group lost about 10% of body weight, over roughly four to five months.

By the end of the study, participants in every group had significantly reduced body fat, and insulin sensitivity improved across all three diets. Liver fat, however, fell by an average of 67% among people on keto, compared with 45% in both the Mediterranean and plant-forward groups. Over a 24-hour tracking period, the keto group showed the largest rise in glucagon, a hormone that helps reduce fat stored in the liver, and the greatest decline in blood insulin. "The most surprising finding was that participants in the ketogenic diet group didn't experience an increase in blood fat or cholesterol levels despite consuming the most fat," said Max Petersen, the study's first author at Washington University School of Medicine.

After the intervention, about 50% of participants on the ketogenic diet no longer met the criteria for prediabetes, compared with 29% on the Mediterranean diet and 7% on the plant-forward diet. The research was supported by the National Institutes of Health and the Foundation for Barnes-Jewish Hospital.