For people trying to improve their health through weight loss, the number on the scale is often treated as the main measure of success.
A new clinical trial suggests there may be more to the story.
Researchers found that people with obesity, prediabetes and fatty liver disease lost roughly the same amount of weight on three different diets. Yet the amount of fat stored in their livers fell much more among those following a ketogenic diet.
The finding is notable because it suggests that weight loss alone may not explain every metabolic change that happens during dieting.
The Diets Produced Similar Weight Loss
The trial, published August 27 in Cell Metabolism, involved adults with obesity, prediabetes and fatty liver disease. Researchers compared three eating patterns: a very-low-carbohydrate ketogenic diet, a Mediterranean diet and a very-low-fat, plant-forward diet.
The diets were deliberately very different.
People following the ketogenic diet got about 4% of their calories from carbohydrates and 73% from fat. The Mediterranean diet provided about 50% of calories from carbohydrates and 35% from fat, while the plant-forward diet supplied about 70% from carbohydrates and 15% from fat.
Despite those differences, participants in all three groups were guided toward losing about 10% of their starting body weight. Researchers adjusted their calorie intake individually to reach that target.
That detail matters because it allowed the researchers to look beyond weight loss itself. If one diet had produced substantially more weight loss, it would have been difficult to determine whether its other benefits simply came from losing more weight.
Instead, the weight loss was similar.
The biggest difference appeared when researchers looked at the liver.
Liver Fat Fell Dramatically On Keto
Participants following the ketogenic diet had an average 67% reduction in liver fat.
For those on the Mediterranean and plant-forward diets, liver fat fell by about 45%.
Liver fat, also called hepatic steatosis, occurs when too much fat accumulates inside liver cells. It can be closely linked with insulin resistance, obesity and other metabolic problems, and it may progress to more serious liver disease in some people.
The researchers also saw a larger improvement in the liver’s response to insulin among the ketogenic-diet participants.
Insulin is the hormone that helps move glucose from the bloodstream into cells. When the liver becomes resistant to insulin, it can continue releasing glucose into the blood even when the body has enough. Improving that sensitivity can therefore help the body manage blood sugar more effectively.
The keto group showed a two- to threefold greater improvement in liver insulin sensitivity than the other groups.
Blood Sugar Improved Alongside The Liver
The changes were not limited to liver fat.
Researchers monitored participants’ blood glucose over a 24-hour period and found that average glucose levels fell by about 20% in the ketogenic group, compared with about 8% in the other two groups.
The difference also showed up in prediabetes.
By the end of the four- to five-month intervention, about half of the people following the ketogenic diet no longer met the criteria for prediabetes. That compared with 29% of those on the Mediterranean diet and 7% of those following the plant-forward diet.
Prediabetes means blood sugar is higher than normal but has not yet reached the level used to diagnose type 2 diabetes. For some people, it can progress to diabetes over time.
The researchers believe the very low carbohydrate intake may help explain why the keto group experienced these additional changes.
With so few carbohydrates coming in, the body shifts toward using more fat for fuel. The study also found a larger increase in glucagon among people following the ketogenic diet. Glucagon is a hormone involved in regulating blood sugar and helping the body mobilise stored fat.
Those metabolic changes may have contributed to the larger reduction in liver fat.
The Findings Have Important Limits
The results are striking, but they do not mean everyone should switch to keto.
The study was small. Although 55 adults were initially assigned to the three diets, the reported analysis included 42 participants. All had obesity, prediabetes and fatty liver disease, so the findings cannot automatically be applied to people without those conditions.
The study was also highly controlled. Researchers provided participants with their food and worked with them regularly with the help of a dietitian.
That is very different from trying to follow a ketogenic diet independently, where maintaining such a strict carbohydrate limit can be considerably harder.
There is also the question of time.
Participants followed the diets for only around four to five months. The study therefore cannot establish whether the larger reduction in liver fat would continue for years, or whether people could maintain such a restrictive eating pattern over the long term.
And while reducing liver fat is an encouraging metabolic change, it is not the same as proving that a diet prevents cirrhosis, liver cancer or other serious complications.
Those questions will require larger and longer studies.
For now, the trial offers a more complicated picture of what happens when people lose weight. The participants reached a similar target on the scale, but their livers responded differently depending on what was on their plates.
That difference may matter particularly for people whose weight problems come with prediabetes and excess liver fat, where improving metabolism involves more than simply
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