Real food, not a diet fad photo: closer to what the trial's kitchen actually served its ketogenic group.
DanaTentis
Illustrative: not a photograph of the actual WashU trial kitchen or a study participant's meal. It represents the kind of whole food the ketogenic arm was fed under total food provision.
At the Same Weight Loss, Keto Cut Liver Fat 67 Percent Versus 45 for Two Other Diets
I read a lot of diet comparison studies, and most of them are secretly weight loss comparisons in disguise, since almost any diet that gets someone to eat less produces roughly the same results everywhere in the body. A new trial out of Washington University in St Louis is different, because the researchers controlled for weight loss itself. Fifty five adults with obesity, prediabetes and fatty liver were fed one of three diets for about 5 months, and everyone lost close to the same 10 percent of their starting body weight. That is what makes what happened next worth paying attention to.
- A Washington University trial gave 55 adults with obesity, prediabetes and fatty liver 100 percent of their food for about 5 months, on a ketogenic, Mediterranean, or low fat plant forward diet.
- Everyone lost about the same 10 percent of body weight, and muscle insulin sensitivity improved by about 50 percent in every group.
- The liver disagreed. Keto cut liver fat 67 percent versus 45 percent on the other two diets, and 50 percent of the keto group reversed their prediabetes versus 29 percent and 7 percent on the other two diets.
- This is one 55 person trial at one site, and the Mediterranean group actually lost more fat and kept more muscle, so keto did not win on every measure.
The trial that removed the guesswork
This was a controlled feeding trial, which is the rare and expensive kind of study that actually earns the word controlled. Participants did not just get a meal plan. The research kitchen handed them 100 percent of their food for the entire study, and they met with a dietitian every week. That matters because adherence, not diet composition, is usually what breaks a diet comparison. Here it was solved by design. The three arms were a very low carbohydrate ketogenic diet, a Mediterranean diet, and a high carbohydrate, very low fat, plant forward diet. The results were published August 27, 2026 in Cell Metabolism.
Where the three diets tied
On several measures, it genuinely did not matter which diet people ate. All three groups lost about 10 percent of their starting body weight. Muscle insulin sensitivity improved by roughly 50 percent from baseline in every group, and blood cholesterol profiles came out similar across all three diets. The researchers' read on this is that the muscle result tracked the weight loss itself, not the specific mix of carbohydrate, fat and protein each group was eating.
Where the liver disagreed
The liver told a completely different story, and it favored keto specifically. Liver fat fell 67 percent in the ketogenic group versus 45 percent in the other two diets. Liver insulin sensitivity improved 2 to 3 times more on keto. Twenty four hour blood glucose dropped 20 percent on keto versus 8 percent on the other diets, and twenty four hour insulin dropped 74 percent on keto versus 44 percent on Mediterranean and 27 percent on the low fat diet. Half of the people on keto reversed their prediabetes entirely, compared with 29 percent on Mediterranean and just 7 percent on the low fat plant forward diet. The mechanism the researchers point to is straightforward. With very little carbohydrate coming in, the liver has less raw material to turn into fat, and the pancreas does not have to pump out as much insulin to keep blood sugar in range.
Keto
Adults who reversed their prediabetes over the trial's roughly 5 months.
Mediterranean
The same measure, the same time frame, on a Mediterranean diet.
Low fat, plant forward
The same measure on a high carbohydrate, very low fat diet.
55 adults with obesity, prediabetes and fatty liver, Washington University in St Louis, a controlled feeding trial with 100 percent of food provided, published August 27, 2026 in Cell Metabolism.
Honest caveat
This trial had 55 people, ran about 5 months, and was done at one site, with no replication yet, so it cannot say anything about long term safety or adherence outside a research kitchen. The body composition trade runs the other way from the liver result. On the Mediterranean diet, participants saw greater reductions in fat mass and smaller reductions in fat free mass, meaning they kept more muscle and bone. Any summary that says keto simply won is misleading. It won on the liver and lost on body composition. Cholesterol came out similar across all three diets, which is reassuring on the usual worry about keto and LDL, but at 55 people over 5 months a null result on cholesterol is weak evidence, not a clean bill of health. The most enthusiastic outside quote in the coverage came from a career ketogenic diet researcher who was not involved in the trial and is not a neutral referee. The senior author discloses advisory board fees and grant support from several metabolic drug companies, none of which sell diets, but disclosed here because it should be. And everyone in this trial had their food handed to them and met a dietitian weekly, so it measures what these diets do when adherence is solved, not what happens when you are shopping and cooking for yourself.
What this means for you
If you are dealing with fatty liver and prediabetes together, which describes a large share of adults with obesity, this trial is a genuine reason to talk to your doctor about a short, targeted period of carbohydrate restriction rather than treating keto as a permanent identity. One of the outside researchers quoted alongside this study framed it as a tool for people who need to bring liver fat down on a real deadline, before surgery for example, and that is a more specific and defensible use of keto than open ended lifestyle advice. It is also worth knowing that the Mediterranean group came out ahead on body composition, losing more fat and keeping more muscle and bone, so this is not a case where one diet wins across the board. And because this trial handed people all of their food, it tells you what keto can do for your liver when adherence is not the problem. It does not tell you how easy that is to sustain on your own.
Primary sources
- Petersen MC, Smith GI, Farabi SS, Palacios HH, Mahalakshmi S, Hellerstein MK, Patterson BW, Klein S. "Effect of diet macronutrient content on the cardiometabolic response to weight loss: A randomized clinical trial." Cell Metabolism, published August 27, 2026.
- WashU Medicine news release, "Low carb diet delivers added liver benefits beyond weight loss," August 27, 2026.
- Scientific American, "Is the Keto Diet Better Than the Mediterranean? New Clinical Trial Reveals Health Benefits," August 27, 2026.
Common questions
Does this study prove keto is the best diet?
No. It shows keto produced a bigger improvement in liver fat and blood sugar control than Mediterranean or low fat diets, at the same amount of weight loss. But the Mediterranean group lost more fat and kept more muscle and bone, so keto did not win on every outcome, and this was 55 people at one site for about 5 months, which is far from the last word.
Do I need to eat this way forever to get the liver benefit?
This trial cannot answer that. It ran for about 5 months with all food provided, so it shows what a supervised period of eating this way can do, not what happens over years or what happens once you are shopping and cooking for yourself. One outside researcher framed a result like this as support for a short, targeted period of carbohydrate restriction rather than a permanent identity.
Who does this actually apply to?
The participants all had obesity, prediabetes and a fatty liver confirmed by imaging, so this is a study of people managing a specific metabolic problem, not a general population weight loss comparison. If that combination does not describe you, the results may not transfer.
Stay Curious.
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