A controlled clinical trial found that three very different diets produced similar weight loss and improved overall metabolic health.
Participants following a very low-carbohydrate ketogenic diet saw larger reductions in liver fat and greater improvements in blood sugar control.
The study was small and highly supervised, so researchers have not established whether the results can be maintained under everyday conditions.
Dieting sort of seems old-fashioned now that people trying to lose weight are flocking to GLP-1 drugs like Ozempic and Wegovy, but researchers have found a diet that might have added health benefits.
New research has found that a very low-carbohydrate diet may provide additional benefits for people with obesity, prediabetes and fatty liver disease.
In a randomized clinical trial, researchers at Washington University School of Medicine in St. Louis compared the effects of three diets with sharply different proportions of carbohydrates, fat and protein.
All three helped participants lose about the same amount of weight. However, the ketogenic diet produced greater improvements in liver health and blood sugar control, the researchers reported. The findings were published in the journal Cell Metabolism.
The researchers recruited 55 adults with obesity, prediabetes and excess fat in the liver. Participants were randomly assigned to follow one of three diets for approximately five months:
A very low-carbohydrate, high-fat ketogenic diet;
A high-carbohydrate, low-fat, plant-forward diet; or
A Mediterranean diet with a more balanced mix of carbohydrates and fat.
The study was more tightly controlled than most diet research. Participants received all their food from the researchers and met with a dietitian each week, making it easier for them to stick to their assigned eating plans.
Weight loss helped every group
Participants in all three groups lost approximately 10% of their starting body weight. Muscle insulin sensitivity—the ability of muscle cells to respond to insulin—improved by about 50% across the three groups.
Because those improvements were similar despite the diets’ different compositions, researchers said weight loss itself appeared to be the main factor improving insulin resistance in muscle.
“Weight loss—even just a moderate amount—is universally beneficial in people who are metabolically unhealthy,” said Max Petersen, an assistant professor of medicine at WashU Medicine and the study’s first author.
The results differed when researchers examined the liver, however.
Liver insulin sensitivity improved two to three times more among people on the ketogenic diet than among participants following either of the other diets. The ketogenic group also reduced liver fat by 67%, compared with a 45% reduction in the Mediterranean and plant-forward groups.
That difference could be important for people with metabolic dysfunction-associated steatotic liver disease, commonly called fatty liver disease. The condition can progress to liver inflammation, scarring and cirrhosis.
Blood sugar also improved
The ketogenic diet produced the largest improvement in glucose control. Average 24-hour blood sugar levels fell 20% from the start of the study in that group, compared with 8% in each of the other groups.
Daily insulin levels declined 74% among participants following the ketogenic diet. By comparison, insulin fell 44% in the Mediterranean group and 27% in the plant-forward group.
Half of the ketogenic-diet participants no longer met the criteria for prediabetes at the end of the trial. That compared with 29% of people following the Mediterranean diet and 7% of those on the high-carbohydrate diet.
What consumers should know
The findings do not mean a ketogenic diet is the best choice for everyone. The trial included only 55 people with a specific combination of obesity, prediabetes and fatty liver disease. It also lasted about five months and provided participants with all their meals—conditions that may be difficult to reproduce at home.
Strict ketogenic diets can also be difficult to sustain and may require adjustments for people taking diabetes or blood-pressure medications. Consumers considering a major reduction in carbohydrates should consult a doctor or registered dietitian, particularly if they have diabetes, kidney disease, liver disease or another chronic condition.
The broader conclusion may be more encouraging: All three diets improved metabolic health when they produced meaningful weight loss. But for people with obesity and fatty liver disease, the study suggests that carbohydrate intake could influence some health outcomes independently of the number on the scale.