Researchers dug into the data, comparing the Mediterranean, keto and plant-based diets.
Reviewed by Dietitian Madeline Peck, RDN, CDN
Key Points
- The ketogenic diet is a high-fat, very low-carbohydrate dietary approach.
- New research found that the ketogenic diet showed signs of improved cardiometabolic markers.
- Still, the keto diet can make it more difficult to reach other beneficial nutrition goals.
The first time I encountered the ketogenic diet was in an office setting, before I became a dietitian. One morning in the breakroom, I was making myself a cup of coffee, when I overheard a coworker raving about how much he was loving his new “keto” diet. Once I got back to my desk, I immediately opened Google and searched the diet. As you can imagine, my first thought was “…No carbs?!”
At this point, I’ve learned quite a bit more about the ketogenic diet—a high-fat, very-low-carbohydrate and moderate-protein dietary approach designed to induce nutritional ketosis. Originally, the diet was created to help manage seizures in children with epilepsy, as ketosis appears to alter how the brain uses energy. But while the diet was developed for a very specific medical purpose, it has since been adapted and adopted by many people in hopes of losing weight.
And while many popular diets—including the Mediterranean diet, plant-forward diets and the keto diet—are often touted for their weight-loss potential, new research suggests that the type of diet you follow may affect more than just the number on the scale. In fact, a new study published in Cell Metabolism found that while participants lost similar amounts of weight following a Mediterranean, plant-based or keto diet, that the keto diet was associated with greater improvements in certain measures of cardiometabolic health than the other diets.
So, what was it about the keto diet that appeared to give it an edge when it came to some markers of metabolic health? Let’s break down what the researchers found.
How Was the Study Conducted?
In this randomized clinical trial, researchers set out to determine whether three popular diets—each with a considerably different macronutrient composition—had diet-specific effects on cardiometabolic health. The three diets studied included:
- The ketogenic, or keto, dietwhich was very high in fat and very low in carbohydrates.
- The Mediterranean dietwhich provided a more moderate balance of carbohydrates and fat.
- The low-fat, plant-forward dietwhich was very low in fat and higher in carbohydrates.
The study included 42 adults with obesity, prediabetes and fatty liver disease. Each participant was randomly assigned to follow one of the three diets. Additionally, the researchers tailored each participant’s calorie intake so that everyone lost approximately 10% of their body weight, regardless of which diet they followed. The participants received all of their meals from the research team and met with a dietitian weekly to help them stick to their assigned diet.
While each of the diets provided similar amounts of calories, their macronutrient compositions differed substantially. The ketogenic diet provided about 73% of calories from fat and just 4% from carbohydrates. The Mediterranean diet provided 35% of calories from fat and 50% from carbohydrates, and the plant-forward diet was lowest in fat, with 15% of calories from fat and 70% from carbohydrates.
Because all three diet groups were intentionally placed in a calorie deficit and lost a similar amount of weight, the researchers were able to examine whether what participants ate mattered for metabolic health, even if the amount of weight lost was the same.
What Did the Study Find?
After studying the effects of similar amounts of weight loss achieved through three popular diets with very different macronutrient compositions, researchers found that the ketogenic diet appeared to provide some additional metabolic benefits, particularly in the liver, compared with the Mediterranean and plant-forward diets.
Each group lost about 10% of their body weight, and researchers observed an approximately 50% increase in muscle insulin sensitivity across all three groups. In other words, when it came to how well the muscles responded to insulin, the diets performed similarly. However, the results looked different when researchers examined insulin sensitivity specifically in the liver. Those on the ketogenic diet experienced a greater improvement in hepatic insulin sensitivity, and the keto group also experienced greater reductions in liver fat.
Additionally, the ketogenic diet appeared to have a slight upper hand when it came to blood sugar levels. Participants following the keto diet experienced greater reductions in hemoglobin A1c levels, as well as their 24-hour blood glucose and insulin levels. In fact, half of the participants following the ketogenic diet no longer met the criteria for prediabetes after the intervention, compared with 29% of those following the Mediterranean diet and 7% of those following the plant-forward diet who no longer met prediabetes criteria.
Interestingly, though, the ketogenic diet did not appear to have a significant advantage when it came to other health markers. For example, researchers found no significant differences between the three groups in LDL (“bad”) cholesterol levels or apolipoprotein B–another marker of heart health.
While the keto diet does show some promise, it’s important to note that this study did have limitations, including its very small sample size of only 42 participants. The study was also designed to examine the three diets during weight loss, so it was difficult for researchers to determine whether the liver-related benefits associated with the ketogenic diet would continue during weight maintenance or whether someone would experience similar benefits by starting a ketogenic diet after losing weight.
How Does This Apply to Real Life?
While the ketogenic diet was associated with some improvements in cardiometabolic health, it’s important to remember that it’s a highly restrictive dietary pattern that drastically limits an important macronutrient group—carbohydrates. And while you may think of pasta and bread when you hear “carbohydrates,” this macronutrient group encompasses much more than that, including essential sources of fiber and micronutrients such as fruits, vegetables, legumes and whole grains. In fact, research suggests that following a ketogenic diet may affect the diversity of the gut microbiome and make it more difficult to maintain social flexibility around food.
Plus, while this specific study showed some benefits associated with following the keto diet, researchers observed weight loss and improvements in metabolic health across all three diets. This means that a person doesn’t necessarily need to follow a ketogenic diet to see health benefits from losing weight.
So while the keto diet appeared to have an advantage when it came to certain measures of liver health and blood sugar, that doesn’t necessarily mean it’s the best choice for everyone. The best dietary pattern is one that you can follow consistently and that provides the nutrients your body needs. For some people, that may be a ketogenic diet—for others, a Mediterranean or plant-forward approach may be more enjoyable and sustainable.
Our Expert Take
In a new study published in Cell Metabolismresearchers found that of the three different dietary patterns, a very-low-carbohydrate ketogenic diet produced greater improvements in certain measures of metabolic health compared with the Mediterranean diet and a plant-forward diet. That said, these findings don’t mean that everyone should follow a ketogenic diet for weight loss and improved health markers.
The keto diet is highly restrictive and can be difficult to sustain long term, while the Mediterranean and plant-forward diets offer a wider variety of carbohydrate-rich foods, including whole grains, fruits, legumes and vegetables. All three of the diets did support weight loss as well as improvements in some measures of metabolic health, meaning that they can all support improved overall health. The best dietary pattern is the one that supports your health while also being realistic and enjoyable for you to follow consistently.