September 1, 2026
Three diets caused equal weight loss, but one had a clear advantage for the liver
Keto cut liver fat by 67% in a clinical trial, compared with 45% on Mediterranean and plant-forward diets despite equal weight loss
ByEric Ralls
Founder
Losing weight is supposed to be the thing that clears fat out of a liver, and all three diets in a new clinical trial produced the same weight loss. Inside the liver, they didn’t
Adults with obesity, prediabetes and fatty liver disease each lost about 10% of their body weight. Liver fat then fell by 67% in the group eating almost no carbohydrate, and by 45% in the two groups that kept eating it
Weight loss did most of the work. But the diet they followed while losing it changed what happened in the liver
The trial ran at WashU Medicine, where the research team supplied every meal for about five months. Fifty-five adults were randomly assigned to a ketogenic, Mediterranean or very-low-fat plant-forward diet. Forty-two finished and were included in the main analysis, 14 in each group
“For patients with obesity, prediabetes and fatty liver disease, weight loss induced by a very low-carbohydrate diet provides additional therapeutic effects on glucose and lipid metabolism that should further help prevent the progression to more severe metabolic diseases than weight loss alone,” said Samuel Klein, the study’s senior author
Study supplied every meal
Most diet trials ask people to change what they buy and cook. This one handed them the food. Participants picked up packed meals and met with a study dietitian every week. Participants logged eating more than 95% of their assigned meals and snacks
The three plans were about as far apart as popular diets get. Per 2,000 calories, the ketogenic meals provided 20 grams of carbohydrate, the Mediterranean meals 254, and the plant-forward meals 352. That’s the gap between a day with no bread, rice or fruit in it and a day built around all three
Fat made up 73% of calories on keto, 35% on the Mediterranean plan and 15% on the plant-forward one. Everyone started at an average of about 250 pounds (113 kg) and lost roughly 25 pounds (12 kg) over four to five months. No group got there faster than the others
Muscle improved on all three diets
Insulin moves sugar out of the blood and into cells. In people with prediabetes, muscle stops responding to insulin properly. Weight loss fixed a good deal of that, whatever was on the plate
Muscle insulin sensitivity rose by roughly 50% in all three groups, with no meaningful gap between them. Fasting glucose and insulin fell everywhere too
Klein said, “But all three diets – despite vastly different macronutrient makeups, from very low carbohydrates to very high carbohydrates – successfully improved metabolic health through weight loss alone.”
Liver fat dropped most on keto
The liver is where the three plans stopped matching. Liver fat fell 67% on the ketogenic diet and 45% on each of the others. The liver’s own response to insulin improved two to three times more on the very-low-carb plan
Max Petersen, an assistant professor of medicine at WashU, is the study’s first author. “Fatty liver disease affects about 75% of adults with obesity worldwide and has become the fastest-growing cause of chronic liver disease and liver cirrhosis,” Petersen said. “Our study shows that for people with obesity and fatty liver disease, a low-carbohydrate ketogenic diet could help reduce that statistic.”
The team also measured how much new fat the liver was building from scratch. The liver made less new fat on the ketogenic and Mediterranean diets but not on the plant-forward one, and the fall was steepest on keto
Keto improved prediabetes measures
Half the people on the ketogenic diet no longer met the criteria for prediabetes at the end, compared with 29% on the Mediterranean diet and 7% on the plant-forward one
Sampling around the clock showed the same pattern. Average insulin also fell, dropping 74% on keto compared with reductions of 44% and 27% on the other diets
One thing the low-carb diet did not do was repair the pancreas. After a sugar drink, the pancreas released as much insulin as it had before the weight loss, in every group. Months of cutting carbs did not improve how those cells work
Cholesterol fell across all diets
A diet drawing 73% of its calories from fat, and 23% from saturated fat alone, is the kind of eating plan that raises questions about the heart. The ketogenic meals provided 749 milligrams of cholesterol a day, against 16 on the plant-forward plan
In this trial, none of that raised cholesterol. Total and LDL cholesterol both fell after weight loss, and so did apolipoprotein B, with no difference among the three groups. Triglycerides measured across a full day showed no group difference either
Fasting triglycerides fell furthest on keto, and HDL cholesterol did not drop there while it did on the other two plans
That’s a narrower claim than it sounds. The finding covers five months of supplied meals in 42 people, not a lifetime of low-carb eating as anyone actually does it. Other trials of keto have reported LDL rising instead
Big questions remain unanswered
The research team provided every participant’s food, which is the trial’s strength and its limit. Adherence above 95% isn’t what a ketogenic diet looks like when a person is traveling and eating out
The authors also said 14 people per group is small enough that real differences between the diets could have been missed
Two questions the trial wasn’t built to answer are the ones a patient would ask first. The authors can’t say whether a gentler carbohydrate cut, one that stops short of ketosis, does the same work for the liver. Nor can they say whether the diet has to be in place during the weight loss itself, or would deliver the same metabolic health benefits started afterward
“Many metabolically unhealthy patients also are candidates for GLP-1 medicines, which have been very useful tools for helping people lose weight. But our results show that choice of diet remains important because it has an impact on specific health outcomes that go beyond weight loss alone,” Petersen said
The full study was published in the journal Cell Metabolism
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