Keto diet cuts liver fat most in clinical trial

Every meal was decided before it reached the table. At Washington University School of Medicine in St. Louis, a research team assigned 42 people with obesity, prediabetes and fatty liver disease to one of three diets, supplied all their food and checked in with them weekly. After four to five months, the ketogenic group had cut liver fat by an average of 67%—more than either comparison group.

The researchers designed the diets to produce the same amount of weight loss: about 10% of body weight for every participant. The ketogenic plan supplied 4% of calories from carbohydrates and 73% from fat. The Mediterranean diet supplied 50% from carbohydrates and 35% from fat, while the low-fat, plant-forward diet supplied 70% from carbohydrates and 15% from fat.

All three diets reduced body fat and improved the participants' sensitivity to insulin, which helps the body regulate blood sugar. But the liver results separated them: fat fell by 45% in both the Mediterranean and plant-forward groups. About 50% of participants on keto no longer met the study's prediabetes criteria, compared with 29% on Mediterranean and 7% on the plant-forward diet.

The measurements offer a possible explanation for the gap. Over 24 hours of blood testing, the keto group had the largest increase in glucagon, a hormone that promotes fat loss in the liver, and the greatest reduction in blood insulin levels. The result also challenged one expectation in this trial: participants eating the most fat did not experience an increase in blood fat or cholesterol levels, according to the researchers.

So what changes in practice? For people with obesity, prediabetes and fatty liver disease, the study suggests that the composition of a calorie-controlled diet may affect metabolic health beyond weight loss alone. But this was a 42-person clinical trial in which researchers provided every meal, and its results cover only the four-to-five-month intervention. The findings are a targeted signal for care, not a universal prescription for everyone considering a keto diet.