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Ask a nutrition researcher which diet works best for weight loss, and they’re likely to say, “whichever one you can stick to.” Some diets test your resolve to the limit, especially if they lack your favorite foods, so most head-to-head comparisons end up measuring willpower more than anything else.
To get around this problem, a team at Washington University cooked and delivered every meal the participants in their study ate for 5 months. They then matched weight loss across three very different diets to see what the differences between them were. The results were surprising.
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Let’s find out why!
Tim Snaith
Newsletter Editor, Healthline
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Written by Tim Snaith
September 17, 2026 • 2 min read
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How keto shows up in the liver
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The researchers fed 55 adults one of three diets for about 5 months. Everyone in the trial had obesity, prediabetes, and extra fat sitting in the liver. One group ate very low carb, with only 4% of calories from carbs. Another group ate the Mediterranean diet, with 50% of calories from carbs. One ate very low fat, with 70% of calories from carbs and most of the food coming from plants. Portions were designed so that each group lost about one-tenth of their body weight.
By most measures, the diets finished in a draw. Blood sugar handling improved by roughly the same amount in every group, so the weight loss was making a difference there.
The liver was where differences showed up. Fat inside this most vital of organs fell by 67% on the low carb diet, against 45% on the other diets. By the end, around half the low carb group no longer counted as prediabetic. On the Mediterranean diet, that figure was a less impressive 29%, and on the very low fat diet, it was only 7%.
Insulin is the likely reason. Your body releases it in response to carbs, and one of its functions is to signal the liver to store fat. The keto meals had almost no carbs, so insulin levels throughout the day dropped by nearly three-quarters, while a second hormone, glucagon, which tells the liver to burn fat, rose instead.
Interestingly, although the keto group ate far more saturated fat than anyone else, their cholesterol and blood fat levels held steady. This group also consumed 23% of their calories as protein, compared with 15% for the other groups.
Before you clear your shelves of carbs, bear in mind that only 42 of the 55 people completed the full 5 months on these strict diets, and that every meal was cooked and delivered for them by trained nutritionists. Plus, the senior author also advises several drug companies working in this area, so there may be a conflict of interest.
Keto isn’t right for everyone, so you should talk with your doctor before starting out on your own. But what this research does appear to show is that even though many diets can help you lose weight, low carb has distinct benefits for people with prediabetes and elevated liver fat.
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Want to learn more about food, diets, cooking, or some other nutrition subject? Let us know at nutritionedition@healthline.com, and we’ll look into it for you! (Heads-up: We may use your response in an upcoming newsletter.)
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What we’re digesting
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