When people lose the same amount of weight, do they receive the same metabolic benefits regardless of which diet they follow?
A newly published randomized clinical trial suggests the answer may be no.
Researchers compared three distinctly different eating patterns in adults living with obesity, prediabetes and excess fat within the liver:
• A very-low-carbohydrate ketogenic diet
• A Mediterranean diet
• A very-low-fat, plant-forward diet
All three diets produced approximately the same 10% reduction in body weight. Every group also improved its overall metabolic health.
However, what happened inside the liver was remarkably different.
Keto Produced the Greatest Reduction in Liver Fat
The trial was conducted by researchers at Washington University School of Medicine and published in Cell Metabolism in August 2026.
Fifty-five adults with obesity, prediabetes and fatty liver disease were randomly assigned to one of the three diets for approximately five months. Participants received all their food throughout the study and met regularly with a dietitian, giving researchers unusually strong control over dietary adherence.
Although weight loss was deliberately matched across the groups, liver fat decreased by an average of:
• 67% on the ketogenic diet
• 45% on the Mediterranean diet
• 45% on the plant-forward, very-low-fat diet
This is an important distinction. The finding does not mean that fatty liver was completely eliminated in 67% of participants. It means the keto group experienced an average 67% relative reduction in the amount of fat stored within the liver.
Nevertheless, the difference was substantial.
Blood Sugar and Insulin Also Improved
The ketogenic group experienced the greatest improvement in several other metabolic measurements.
Over approximately five months:
• Twenty-four-hour blood glucose decreased by 20% in the keto group, compared with around 8% in the other groups
• Daily insulin levels decreased by 74% with keto, compared with 44% on Mediterranean and 27% on the low-fat diet
• Half of the keto participants no longer met the criteria for prediabetes
• Prediabetes was no longer detected in 29% of the Mediterranean group and 7% of the low-fat group
Insulin sensitivity within the liver improved two to three times more with the ketogenic diet than with the other two approaches.
Muscle insulin sensitivity, however, improved by approximately 50% in all three groups. This suggests that weight loss itself was largely responsible for the improvement within muscle tissue, while restricting carbohydrates may have produced an additional effect within the liver.
How Could Keto Reduce Liver Fat More?
The liver helps regulate blood glucose and stores excess energy.
When carbohydrate intake is high—particularly from added sugars and refined carbohydrates—the liver may convert some of that excess energy into fat through a process known as de novo lipogenesis.
A ketogenic diet dramatically restricts carbohydrates. In this study, only around 4% of total calories came from carbohydrate, while approximately 73% came from fat.
This substantially reduced the body’s requirement for insulin and appears to have reduced the production and storage of new fat within the liver.
The study found that hepatic de novo lipogenesis, glycated haemoglobin, glucose and insulin decreased most in the very-low-carbohydrate group.
Despite the high fat intake, researchers reported no significant differences between the three groups in LDL cholesterol, apolipoprotein B or 24-hour triglyceride concentrations during this trial.
Does This Mean Keto Is Better Than the Mediterranean Diet?
For short-term reduction of liver fat and improvement in glucose regulation among people with obesity, prediabetes and fatty liver disease, this trial strongly favoured the ketogenic diet.
However, it does not establish that keto is the best lifelong diet for everyone.
The study was relatively small, lasted only around five months and took place under tightly controlled conditions. Every meal was supplied, and participants received weekly dietary support. That is very different from following a restrictive diet independently for many years.
We also need to consider research measuring different outcomes.
An earlier randomized Keto-Med trial involving people with prediabetes or Type 2 diabetes found that both diets improved HbA1c and produced similar weight loss.
Keto reduced triglycerides more, but it also produced higher LDL cholesterol, provided less fibre and resulted in lower intake of several nutrients. Participants considered the Mediterranean diet easier to maintain after the controlled phase ended.
Most importantly, the Mediterranean diet has been tested in much larger and longer clinical trials. The landmark PREDIMED trial involved more than 7,000 adults at elevated cardiovascular risk and found that Mediterranean diets supplemented with extra-virgin olive oil or nuts reduced major cardiovascular events.
Keto currently does not possess equivalent long-term clinical evidence demonstrating a reduction in heart attacks, strokes or cardiovascular deaths.
The Most Important Finding May Be What the Diets Shared
It would be easy to turn this research into another argument between supporters of different diets. However, the three groups had one powerful factor in common: they all achieved meaningful weight loss.
Every diet improved metabolic health.
The ketogenic and Mediterranean approaches can also share several healthy principles:
• Removing added sugars
• Reducing refined grains and highly processed foods
• Eating non-starchy vegetables
• Choosing minimally processed whole foods
• Including high-quality sources of protein and healthy fats
The real question may not be whether one diet is universally superior. It may be which approach offers the greatest benefit for a particular person, condition and stage of treatment.
Someone requiring rapid improvement in liver fat and blood glucose may benefit from a medically supervised, carefully formulated low-carbohydrate intervention.
Someone seeking a varied, nutrient-rich eating pattern that can be sustained over many years may find the Mediterranean diet more practical.
In some cases, a personalised approach incorporating Mediterranean-quality foods with a lower carbohydrate intake may offer a workable middle ground.
Who Should Be Cautious With Keto?
A ketogenic diet can alter blood sugar, blood pressure, fluid balance and medication requirements relatively quickly.
Professional supervision is particularly important for people who:
• Take insulin or glucose-lowering medication
• Use SGLT2 inhibitor medication
• Have kidney, liver, pancreatic or gallbladder disease
• Are pregnant or breastfeeding
• Have a history of disordered eating
• Have significant cardiovascular risk or elevated LDL cholesterol
A diet that produces excellent results in a controlled trial may not be appropriate or safe for every individual.
The Bottom Line
This new research demonstrates that weight loss is not the entire story.
When weight loss was matched, a very-low-carbohydrate ketogenic diet produced a substantially greater reduction in liver fat, insulin levels and 24-hour glucose than either a Mediterranean or very-low-fat diet in adults with obesity, prediabetes and fatty liver disease.
That makes keto a potentially valuable short-term therapeutic strategy for selected individuals.
However, the Mediterranean diet remains supported by stronger long-term evidence for cardiovascular health, greater dietary variety and better sustainability.
The best diet is not simply the one that produces the most dramatic result after five months. It is the one that improves the health outcome that matters, meets the individual’s nutritional and medical needs, and can be followed safely for the required length of time.
Research Sources
Petersen MC, Smith GI, Farabi SS, et al. “Effect of diet macronutrient content on the cardiometabolic response to weight loss: A randomized clinical trial.” Cell Metabolism, 2026.
Gardner CD, Landry MJ, Perelman D, et al. “Effect of a ketogenic diet versus Mediterranean diet on HbA1c in individuals with prediabetes and Type 2 diabetes: The interventional Keto-Med randomized crossover trial.” American Journal of Clinical Nutrition, 2022.
Estruch R, Ros E, Salas-Salvadó J, et al. “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts.” New England Journal of Medicine, 2018.
This article is for educational purposes and is not a substitute for personalised medical advice, diagnosis or treatment.