When losing weight is a necessity, how it is achieved is important. Obesity, defined as the accumulation of fat that can affect health by the European Association for the Study of Obesity (EASO), can bring metabolic diseases such as diabetes, various cardiovascular problems, or metabolic liver disease (formerly, non-alcoholic fatty liver). Although it continues to spread worldwide, both the diagnosis and treatments to alleviate obesity still lack the specificity and effectiveness that other chronic diseases have. This is the case with nutritional approaches, which are still subject to analyses that reveal new insights.
This Thursday, a study is published in Cell Metabolism comparing three diets for weight loss in patients with “metabolically unhealthy” obesity: the ketogenic (popularized as the keto diet), the Mediterranean, and another plant-based. While the keto largely excludes carbohydrates — cereals, legumes, tubers — and the latter especially reduces fats and processed meats, the second is more varied and prioritizes fruits, vegetables, legumes, fish, and healthy fats, such as olive oil. All of them achieved the main goal, reducing the weight of the participants by 10%; however, when comparing the effects of each on various metabolic health indicators, such as liver fat or blood insulin, the ketogenic diet had better results.
As the authors from the University of Washington (United States) emphasize, the nutrients that make up the diet make the difference. Therefore, compared to drugs like Ozempic, active involvement with a tailored nutritional plan remains an option with many more health benefits. “GLP-1 medications are very useful in helping many patients with metabolic problems lose weight; but our results show that diet choice remains important because it impacts health beyond simple weight loss,” notes Max Petersen, one of the authors, in a press release.
Slightly superior effects of the keto diet
The population analyzed in the study, which lasted six months, was only 42 people (14 in each diet), a limiting aspect when assessing the robustness of any study, but the results were significantly positive in all three groups. With weight loss, muscle insulin sensitivity increased by about 50% in all three groups, but the low-carbohydrate ketogenic diet caused a two to three times greater increase in liver insulin sensitivity. All participants, women and men, had obesity, prediabetes, and hepatic steatosis (5% or more triglycerides in the liver measured by magnetic resonance).
Petersen, an endocrinologist, explains in an email that the sample size and duration were small due to the rigor of the methods they used, which ensured high adherence to the diets. During the study, participants could only eat the dishes and snacks, frozen and packaged, prepared on purpose, with very precise macronutrient content — carbohydrates, fats, and proteins — for each diet. “The effects of the ketogenic diet on liver function were so significant that it is unlikely the results would have been different in a larger study; however, it might have allowed us to detect smaller and more subtle effects of the diets,” Petersen acknowledges.
The ketogenic diet also reduced liver triglycerides the most, the production of new fats in the liver, hemoglobin-bound sugar, and glucose and insulin in blood plasma measured over 24 hours, although the differences were small. It was already known that weight loss improves insulin resistance, but they were surprised to observe that the liver responded differently to different diets. According to Petersen, they thought the ketogenic diet might cause harmful alterations in blood cholesterol levels due to its high fat content. “However, we did not observe differences in the effects of the diets on LDL cholesterol (the bad one) or plasma triglycerides,” he points out.
The explanation they find is that the beneficial effect of a high-fat diet on hepatic steatosis (fatty liver disease) could depend on the degree of caloric and carbohydrate restriction. “Not all high-fat diets are ketogenic: significant carbohydrate restriction is required,” he clarifies. In their study, the ketogenic, Mediterranean, and plant-based diets provided 4%, 50%, and 70% of energy from carbohydrates; 73%, 35%, and 15% from fats; and 23%, 15%, and 15% from proteins, respectively.
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Enjoyment, the key to the Mediterranean diet
The food packages provided to participants included, in the ketogenic diet, very low-carbohydrate dishes — not even fruit — such as egg salad, beef with cheese, chicken with spinach, beef stew, or salmon with broccoli. In the Mediterranean diet, they ate oats with almonds and blueberries, red fruit smoothie, quinoa with black beans and corn, or pasta with pesto and chicken. Meanwhile, the vegetarian diet dishes, very low in fat, included oats with apple and banana, potato pie, fruit smoothie, rice with red beans, or vegetable omelet.
Despite the differences in ingredients and, therefore, macronutrients, all dishes had the same calories to achieve the same caloric deficit and similar fat loss. However, eating has a social and pleasure component that cannot be ignored and varies for each type of diet and person. This must be taken into account by those who design personalized diets, aiming for patients to be able to maintain their commitment during the plan’s duration.
Dietitian Mario Gómez Duréndez, founder of Nution, has seen in his patients that the ketogenic diet is unsustainable and generates little adherence. “Today carbohydrates are in any meal, any celebration, and it is very difficult to restrict them,” he explains. He also warns of “carbophobia” and the “rebound effect” it can cause. He says that with the ketogenic diet, not only fat is lost but also muscle glycogen, which needs water to be stored. “That’s why a lot of weight is lost at first, but some people understand that the problem is carbohydrates and fear reintroducing them into the diet,” Gómez says.
Moreover, glycogen is the first energy substrate we use in activities of a certain intensity, and without it, it is easy to feel without energy. “Honestly, I have not met anyone who enjoys a ketogenic diet, but I have met people who do it to compensate for a period of excess, which requires discipline that is hard to maintain and is unnecessary if you know what you have to eat; that is my philosophy,” Gómez notes. The dietitian usually resorts to the Mediterranean diet when referred patients need to reduce triglyceride and cholesterol levels.
Daniel, 47 years old, is not Mario’s patient but has gone through different diets to lose weight in recent years, achieving the goal several times. In his experience, what works are “simple, varied dishes that you like and can incorporate into your daily life.” He identifies it as a Mediterranean diet with carbohydrates and proteins “slightly adjusted to achieve weight loss.” The hardest part for him is giving up snacking between meals and when going out, but agreeing with his nutritionist on some controlled flexibility, moving more, and seeing results helps him commit.
Miguel Ángel Martínez González, one of the coordinators of the largest clinical study on the cardiovascular preventive effects of the Mediterranean diet (PREDIMED), is clear: “The ketogenic diet is torture, the Mediterranean is enjoyment.” He also recalls in a call with EL PAÍS that the ketogenic diet “does not have nearly the scientific evidence that the Mediterranean diet has.” While PREDIMED was conducted with 7,447 patients over several years, the study published today was done with 42 people in 6 months. The professor at the University of Navarra sees this as a significant limitation and points out that, really, “what they saw in the three diets is very similar” and that “new recommendations should not be made based on these results.”