Losing the same amount of weight did not produce the same health benefits in a new randomized clinical trial. Researchers at Washington University School of Medicine in St. Louis put 55 adults with obesity, prediabetes and excess liver fat on three very different diets. All three groups lost about 10% of their starting weight, but the ketogenic diet showed larger gains in liver fat, liver insulin sensitivity and blood sugar control, according to SciTechDaily.
The finding matters for anyone assuming the number on the scale tells the whole story. Weight loss itself helped every group. The diet composition decided how much extra improvement some measures received. The study was published in Cell Metabolism on 27 August 2026, with support from the National Institutes of Health and the Foundation for Barnes-Jewish Hospital.
Readers following new research on diet and metabolism should know what the trial actually compared, and what it did not. Here is the background a newcomer needs.
What did the study actually test?
Researchers compared three diets with very different macronutrient makeups: a low-carbohydrate, high-fat ketogenic diet, a Mediterranean diet, and a high-carbohydrate, low-fat, plant-forward diet. The 55 participants were adults with obesity who also had prediabetes and excess fat in the liver. This connects to our earlier piece, FDA Approved Lipfendra, the First Oral PCSK9 Inhibitor, for High LDL.
The trial was tightly controlled. Researchers provided all of the participants' food. Participants followed their assigned diets for about five months and met weekly with a study dietitian to stay on plan.
Despite the very different proportions of carbohydrates, fat and protein, all three groups lost about the same amount of weight. That equal loss is what makes the metabolic differences stand out.
Did every diet help?
Yes. All three diets improved metabolic health, and the researchers credit weight loss itself for that shared benefit. "All three diets — despite vastly different macronutrient makeups, from very low carbohydrates to very high carbohydrates — successfully improved metabolic health through weight loss alone," said Samuel Klein, MD, the study's senior author and the Danforth Professor of Medicine and Nutritional Science at WashU Medicine, in the SciTechDaily report.
The clearest shared gain was in muscle. Muscle insulin sensitivity improved by roughly 50% from starting levels across all three groups. Because the improvement was similar everywhere, the results suggest weight loss itself, not the balance of carbohydrates and fat, drove the improvement in muscle insulin resistance.
Where did the ketogenic diet pull ahead?
The liver. Insulin normally signals the liver to reduce the glucose it releases into the bloodstream. In the trial, the liver became more responsive to insulin on all three diets, but the improvement was two to three times greater with the ketogenic diet.
Liver fat fell further on keto as well. After five months, liver fat had dropped 67% in the ketogenic group, compared with 45% in each of the other two groups. That gap could matter for a large group of people: fatty liver disease affects about 75% of adults with obesity worldwide, according to Max C. Petersen, MD, PhD, the study's first author and an assistant professor of medicine at WashU Medicine. He called it the fastest-growing cause of chronic liver disease and liver cirrhosis.
What about blood sugar and prediabetes?
Blood sugar control showed a similar advantage for keto. Blood glucose measured over 24 hours fell 20% from baseline in the ketogenic group, compared with 8% in each of the other groups.
Insulin levels through the day also fell more sharply on keto: down 74%, versus 44% on the Mediterranean diet and 27% on the high-carbohydrate diet. With very little carbohydrate consumed, less insulin is needed to regulate blood glucose, so the pancreas produces less.
The prediabetes results were the most striking. Half of the ketogenic group reversed their prediabetes during the study, compared with 29% of the Mediterranean group and 7% of the high-carbohydrate group.
What do the terms mean?
A few definitions help here:
- Insulin resistance — a state in which the body responds weakly to insulin, the hormone that regulates blood sugar. It is a major feature of prediabetes.
- Prediabetes — blood sugar higher than normal but not yet diabetes. In this trial, some participants reversed it through diet alone.
- Fatty liver disease — excess fat stored in the liver, widespread among adults with obesity.
- Ketogenic diet — a very low-carbohydrate, high-fat diet that sharply cuts the carbohydrate the body takes in.
What does this mean for weight-loss choices?
The results do not suggest the other diets failed. All three groups improved after losing weight, and Petersen called moderate weight loss "universally beneficial in people who are metabolically unhealthy."
But diet choice still matters, he argued, because it affects specific outcomes beyond the scale. "Many metabolically unhealthy patients also are candidates for GLP-1 medicines, which have been very useful tools for helping people lose weight," Petersen said. Readers weighing diet against new weight-loss drugs can see how the economics are shifting in our coverage of the first oral GLP-1, FDA Approved Foundayo: the Oral GLP-1 That Rewrites Obesity Drug Economics. Readers following this should also see FDA Approved Foundayo: the Oral GLP-1 That Rewrites Obesity Drug Economics.
For patients with obesity, prediabetes and fatty liver disease, Klein said weight loss from a very low-carbohydrate diet provides additional therapeutic effects on glucose and lipid metabolism that could help prevent progression to more severe metabolic disease.
What remains unknown?
The trial ran about five months in 55 adults with obesity, prediabetes and liver fat. It does not establish whether the ketogenic advantage holds over years, in other populations, or against every health measure. The study also does not address long-term adherence, which often decides whether any diet works in practice.
Anyone considering a major diet change should ask their doctor a specific question: given my liver and blood sugar results, which diet composition fits my situation? This article is information, not medical or insurance advice.
