August 31, 2026, 12:14 pm | Read time: 7 minutes
Ten percent less on the scale–in theory, it shouldn’t matter to the body whether the pounds are shed through keto, Mediterranean, or low-fat diets. Researchers directly compared these three diets in people with obesity, fatty liver, and prediabetes. The unique aspect: All participants were to lose roughly the same amount of weight. However, what the studies revealed after the weight loss makes the choice of diet suddenly quite interesting.
Why Researchers Wanted to Compare the Three Diets Fairly
Previous studies had already compared keto, Mediterranean, and low-fat diets. Very low-carb diets often resulted in slightly more weight loss after six months, but this advantage diminished over time.1,2 It remained unclear whether the type of diet made a health difference independent of the weight lost, as groups in earlier studies often lost different amounts of weight.
The new study aimed to clarify this: People with obesity, fatty liver, and prediabetes lost about ten percent of their weight with keto, Mediterranean, or a very low-fat, mostly plant-based diet. Researchers then primarily examined the fatty liver and how well the body regulated blood sugar with insulin. Blood lipids and blood pressure were also monitored.3
42 Participants, Three Diets–How the Study Was Conducted
A total of 55 participants were randomly assigned to one of the three diets. Forty-two completed the study and were included in the main analysis–14 per diet. The remaining 13 dropped out during the study, none due to side effects of the diet. The participants who completed the study were, on average, 43 years old.
The differences on the plate were significant. With keto, only four percent of energy came from carbohydrates and 73 percent from fat. The Mediterranean diet consisted of 50 percent carbohydrates and 35 percent fat. The very low-fat, mostly plant-based diet provided 70 percent of energy from carbohydrates and 15 percent from fat.
The Food Came Directly From the Study Team
A unique aspect of the study: The study team provided all meals and snacks. Participants were not to consume other foods or calorie-containing drinks and documented their meals. According to records, more than 95 percent of the planned meals and snacks were actually consumed.
After losing about ten percent of their weight, participants maintained their new weight for three to four weeks. Researchers then repeated the examinations, including determining liver fat content via MRI. They also tested how well insulin worked in muscles and the liver with a special test.
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All lost similar amounts of weight–but there were clear differences in fatty liver
Weight loss was nearly identical across all three groups: Participants lost about ten percent of their body weight on average. Depending on the diet, it took about five months to reach this goal.
Liver fat decreased more with keto
However, there was a clear difference in liver fat. With keto, it decreased by 67 percent, while with the Mediterranean and very low-fat diets, it decreased by 45 percent each.
All three diets were similarly successful in muscles
The effect of insulin in muscles improved by about 50 percent with weight loss from all three diets. The specific diet followed did not make a significant difference. In the liver, however, keto showed a clear advantage: Insulin’s effect improved two to three times more than with the Mediterranean or very low-fat diets.
There were also significant differences in blood sugar and insulin
Researchers monitored blood sugar and insulin not just at a single point in time but throughout the day with three meals. The day-long measured blood sugar dropped by 20 percent after weight loss with keto. With the Mediterranean and very low-fat diets, the decrease was 8 percent each.
The differences were even greater for insulin: Day-long measured levels dropped by 74 percent with keto, 44 percent with the Mediterranean diet, and 27 percent with the very low-fat diet.
Prediabetes disappeared at different rates
There was also a difference in prediabetes. After weight loss, 50 percent of participants on keto no longer met the criteria for prediabetes. For the Mediterranean diet, it was 29 percent, and for the very low-fat diet, 7 percent. The difference between the groups was statistically significant.
Keto was not superior in LDL cholesterol and blood pressure
However, keto did not outperform in all measured values. Changes in LDL cholesterol and blood pressure did not significantly differ between the three diets. This was also true for apolipoprotein B–a component of certain particles that transport fats through the blood–and for triglycerides, or blood fats, measured throughout the day.
What the differences mean for health
The results suggest that for some metabolic changes, weight loss is crucial, while for others, the composition of the diet might also play a role. This was particularly evident in the liver. This is relevant for the participants studied, as they already had fatty liver and prediabetes.
Why keto might have a stronger impact on the liver
A possible explanation comes from measurements of sugar and fat metabolism. With keto, blood sugar and insulin were significantly lower throughout the day, while glucagon increased. Glucagon is a hormone that influences how the liver uses stored energy.
These changes may have led the liver to produce less new fat and break down more existing fat for energy. In fact, the measured new fat production in the liver decreased more with keto than with the other two diets. The authors see this as a possible explanation for the greater reduction in liver fat.
High fat–but no disadvantages in LDL cholesterol and blood pressure
This is also noteworthy because the keto diet was extremely high in fat: 73 percent of energy came from fat, 23 percent from saturated fatty acids. Saturated fatty acids are often criticized for their potential impact on blood fats and cardiovascular risk.
Despite the high fat content, keto did not perform worse in LDL cholesterol, blood pressure, apolipoprotein B, and triglycerides measured throughout the day than the other two diets. Some other values related to cardiovascular risk even improved more with keto.
How meaningful are the results?
A major strength of the study is the nearly identical weight loss in the three groups. This allows the influence of the diet to be better separated from the effect of weight loss itself. Adherence to the respective diet was also very high, at more than 95 percent. Additionally, researchers used elaborate methods to determine liver fat and insulin action.
With 42 participants–only 14 per diet–the study was small. This could mean differences between the diets went undetected, as the authors also point out.
Another point to consider in the evaluation: The researchers initially only defined how well muscles and liver respond to insulin as the main outcomes. Liver fat, blood sugar, blood fats, and many other values were additionally examined. Therefore, the differences in these values are important indicators but less robust than the two main outcomes of the study.
Mediterranean and Keto Diets Compared: Effects on Weight and Blood Pressure
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It remains open how strict keto must be
For practical significance, there is an important open question. The keto diet studied contained only 20 grams of carbohydrates per day at 2,000 kilocalories, making it very low-carb. The study does not show whether a less strict version without ketosis–the typical metabolic shift with very few carbohydrates–would have similar effects.
It is also unclear when keto should be used. Participants were already on a ketogenic diet during weight loss. Whether similar liver benefits occur if keto is adopted only after weight loss to maintain the new weight was not investigated.
The study was funded by grants from the U.S. National Institutes of Health and support from the Foundation for Barnes-Jewish Hospital. Study leader Samuel Klein also reported financial ties to several pharmaceutical companies.