It’s possible to lose weight following any one of three diets, a new clinical trial has found—but one diet stands out for its substantive health benefits that the other eating regimens just don’t seem to offer.
In the trial, researchers put three popular weight-loss regimes—a low-fat, plant-focused diet, the Mediterranean diet and the ketogenic, or keto, diet—to the test. The Mediterranean diet has long been lauded by nutritionists for its health benefits and is high in healthy fats, plants and whole grains. The plant-focused diet used in the trial is similar and highlights plant-based foods. The keto diet is rather different: it is typically high in fat and very low in carbohydrates, with a little protein thrown in for good measure.
Keto diets are specifically intended to limit your body’s access to sugars, forcing it to consume fat for energy by entering a metabolic state called ketosis. They can be used to treat certain diseases, such as epilepsy, and may have some benefits in other psychiatric conditions such as depression and schizophrenia.
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Now, in a new head-to-head clinical study of the three diets, researchers found that people with obesity who lost weight on the keto diet saw better metabolic outcomes than their peers who lost a similar amount of weight on another diet. These benefits included a reduction of liver fat and lower rates of prediabetes.
The trial was small—it involved 55 participants with obesity who were prediabetic and had fatty liver disease. The participants met with a dietician every week, and they got precooked, frozen meals for one of the three diets.
The keto diet that the participants followed was rich in food such as fruits and vegetables, cheese, eggs, meat and fish, says Samuel Klein, the study’s senior author and a professor of medicine and nutritional science at the Washington University School of Medicine in St. Louis. The Mediterranean diet, meanwhile, included items such as fish, chicken, legumes, seeds, nuts and olive oil, and the plant-focused diet included beans, rice, and fruits and vegetables.
Klein and his colleagues weren’t interested in whether the diets helped people lose weight. “That’s already been studied in multiple studies, and the differences are quite small between these three different diets,” Klein says. Instead the team assessed the participants’ health before and after they lost a similar amount of weight—about 10 percent of their starting weight.
All three diets had clear health benefits, such as greater sensitivity of muscle tissue to insulin, says Max Petersen, the paper’s lead author and an assistant professor at the Washington University School of Medicine. Blood cholesterol profiles were also similar across all diets.
But the keto diet had “much more profound beneficial effects on the liver,” Klein says. Participants on the keto diet saw a decrease in the liver’s production of triglyceride, a type of fat that is unhealthy in high amounts, and increased liver insulin sensitivity, which helps regulate blood sugar, as well as a reduction in liver fat.
The latter was a critical metric, Klein says: liver fat can have serious complications, including inflammation and cancer. Half of the participants on the keto diet also saw remission of their prediabetes.
The results suggest that reducing the intake of carbohydrates, particularly sugars, can help people lose weight and support their metabolic health, Klein says. “Reducing sugar intake would be a number one thing to do for anybody ... trying to change their diet to improve their health if they have obesity, independent of weight loss itself,” he says.
The study is well designed, says Jeff Volek, a kinesiologist at the Ohio State University, who was not involved with the study. Research by Volek and others has shown that ketosis can help with liver insulin sensitivity, triglyceride production, and more. The study adds to that body of evidence, he says. “It is nice to see these researchers finally coming around on ketogenic diets, as the evidence has been strong for a long time,” Volek says.
Sai Das, a nutrition science professor at Tufts University, who was also not involved in the study, says that the results suggest keto is a “highly promising” choice for people who need to reduce their liver fat and triglyceride levels ahead of surgery, whether for weight loss or any other chronic condition. “This diet offers a better option to do this in a timely manner,” Das says.
The study’s short timeline and small sample size, however, mean more research is needed to better understand the long-term effects of the keto diet compared with those of other diets, she says. On the Mediterranean diet, she notes, participants saw greater reductions in body fat mass and smaller reductions in fat-free mass, which includes muscles and bones.
Klein, for his part, hopes the results inspire future research combining keto with popular glucagonlike peptide 1 (GLP-1) weight-loss drugs such as semaglutide, tirzepatide, and more.
“All medications have costs and side effects,” he says. “How can we use diet in conjunction with medication to enhance the therapeutic effect with the least amount of cost and least amount of side effects?”
The findings were published on Thursday in the journal Cell Metabolism.