Obesity affects about 40% of adults in the United States and is linked to risks such as type 2 diabetes and fatty liver disease. Dietary interventions remain a primary strategy to support weight loss and improve metabolic health. A study involving 42 participants with obesity, prediabetes, and fatty liver disease compared the effects of a ketogenic diet, Mediterranean diet, and a low-fat, plant-forward diet.
Participants were randomly assigned to one of the three diets, which differed markedly in macronutrient composition: the ketogenic diet provided 4% of calories from carbohydrates and 73% from fat, the Mediterranean diet provided 50% carbohydrates and 35% fat, and the low-fat, plant-forward diet provided 70% carbohydrates and 15% fat. All meals were provided to ensure compliance, and participants met weekly with a dietitian. Caloric intake was adjusted so each group lost roughly 10% of body weight over 4 to 5 months.
The results showed that moderate weight loss around 10% led to improvements in metabolic function, including better muscle insulin sensitivity, across all diet groups. However, differences emerged in specific metabolic parameters depending on the dietary composition.
While all diets improved body fat and insulin sensitivity, the ketogenic diet produced the most pronounced reduction in liver fat content, averaging a 67% decrease. This contrasted with 45% reductions in the Mediterranean and low-fat diet groups.
The ketogenic group displayed the highest increase in blood glucagon, a hormone that regulates blood sugar and promotes fat breakdown in the liver. They also experienced the greatest decrease in circulating insulin levels. Since insulin secretion primarily responds to carbohydrate intake and ketogenic meals had minimal carbohydrates, lower insulin levels throughout the day were expected.
Higher glucagon levels likely resulted from the ketogenic diet's higher protein content stimulating glucagon release and the concurrently lowered insulin levels, which normally suppress glucagon.
These hormonal changes likely underlie the superior reductions in liver fat seen with the ketogenic diet, as increased glucagon promotes liver fat breakdown and decreased insulin reduces liver fat production from glucose.
Further metabolic advantages of the ketogenic diet were evident when examining changes in prediabetes status. Approximately 50% of participants on the ketogenic diet no longer met criteria for prediabetes following the intervention. This compared with 29% in the Mediterranean diet group and only 7% in the low-fat, plant-forward group.
Despite higher dietary fat intake, the ketogenic group did not experience increases in blood fat or cholesterol levels. The minimal carbohydrate content led to substantially lower post-meal blood glucose spikes, resulting in improved measures such as hemoglobin A1c and fasting blood glucose in the ketogenic group.
The study suggests that dietary plans with reduced carbohydrate intake, such as the ketogenic diet, may confer metabolic benefits beyond those achieved through weight loss alone. Improvements in liver fat metabolism and blood sugar regulation were particularly notable.
This insight is relevant amid increasing use of medications targeting GLP-1 pathways for obesity treatment, which focus primarily on weight loss. The findings indicate that diet composition could provide complementary metabolic benefits.
However, the study's small size, short duration, and controlled meal provision limit generalizability. The ketogenic diet's high fat content, especially saturated fat from animal sources, may not be suitable or sustainable for everyone.
Longer-term, larger clinical trials are needed to verify these metabolic advantages and assess their impact on the incidence of conditions like type 2 diabetes.
Until then, this study adds evidence that the balance of macronutrients in a diet plays a critical role in metabolic health beyond calorie restriction and weight loss alone.