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A new controlled clinical study conducted during the pandemic compared the two diets by asking 33 people with prediabetes or diabetes to follow both diets back-to-back for three months. During the first four weeks of each diet, participants received either healthy keto or Mediterranean meal deliveries and then followed their own meal plans.
Researchers monitored participants’ weight, blood sugar (glucose) levels, cardiovascular risk factors, and diet compliance. Which diet was still before the closing bell?
“Both diets improved blood sugar control to a similar extent, and both groups lost similar amounts of weight,” said lead nutritionist Dr. Walter Willett, Professor of Epidemiology and Nutrition at Harvard TH Chan School of Public Health and Professor of Medicine at Harvard Medical School. He was not involved in the study.
The study tracked low-density lipoprotein, or LDL, known as “bad” cholesterol, and triglycerides, another type of fat in the blood that also helps harden arteries.
“The keto diet significantly increased LDL cholesterol by 10%, while the Mediterranean diet decreased LDL cholesterol by 5%,” said Dr. Frank Hu, chair of the Department of Nutrition at Harvard TH Chan School of Public Health, who was not involved in the study.
“The difference between the two diets is quite large, and this can have long-term consequences for cardiovascular disease,” Hu said.
While both diets reduced triglycerides, the keto diet did so more significantly, the study found. However, reducing triglycerides is not as important as increasing bad cholesterol, Hu said.
“High LDL cholesterol is a much stronger and more important risk factor for cardiovascular disease than triglyceride levels,” he said. “While both sides have been fairly effective at short-term glycemic control, I think the main issue is the potential long-term effects of keto on cardiovascular disease.”
“I tried to give every diet the best chance”
Keto achieves rapid weight loss success, according to proponents, by putting people in ketosis, a state in which the body begins burning stored fat for fuel. But to get into ketosis, carbs are drastically reduced to 20 to 50 grams per day. (A cup of cooked rice is about 50 grams.) Eating extra carbs will knock you out of ketosis.
The typical American’s daily diet is 50% carbohydrate, Hu said, so decreasing This inclusion to less than 50 grams is “a tremendous reduction. That is difficult for people to comply with.”
People often think of keto as a “meat” diet, filling their plates with full-fat dairy, sausage, bacon, and other meats with saturated fats, all of which can contribute to inflammation and chronic disease.
However, the study used a “well-formulated ketogenic diet” that limited high protein intake and emphasized non-starchy vegetables, said study author Christopher Gardner, a research professor of medicine at the Stanford Prevention Research Center.
“I’ve tried to give every diet the best chance it can. I wasn’t trying to make it a crappy keto and a good Mediterranean, or a crappy Mediterranean and a good keto,” said Gardner, who is also the director of the clinical and translational research area at the Stanford Diabetes Research Center.
The keto diet prohibits grains, legumes, and fruit except for a handful of berries. However, the Mediterranean diet emphasizes filling your plate with fruits, vegetables, beans, lentils, whole grains, nuts and seeds.
Both diets agree that “we eat way too much added sugar and refined grains, and we don’t eat enough vegetables,” Gardner said. “So the whole study was created to see if there’s a benefit to getting rid of fruits, whole grains and beans on keto — after you’ve done the things everyone agrees on.”
In addition to the increase in bad cholesterol, people in the keto phase had “decreased intakes of thiamine, vitamins B6, C, D, and E, and phosphorus,” as well as “incredibly low amounts of fiber,” said Dr. Shivam Joshi, clinical assistant professor of medicine at New York University Grossman School of Medicine. He was not involved in the study.
“Whole grains and fruits have positive health benefits, and their exclusion from the keto group raises concerns about the long term health effects”, Willett said. In addition, he said, “Many people find that sticking to a ketogenic diet long-term is very important difficult.”
In fact, the study found that most people quit the keto diet after the research ended.
“They had keto delivered to their house. They had a health educator helping them,” Gardner said. “Nevertheless boom! Most people stopped following the keto diet almost immediately (when that portion of the study ended), while many of those who ate Mediterranean diets were still eating this way when the study was over.”
What is the core message of the study?
“The main takeaway message for me is that severe restriction of some healthy carbohydrates isn’t necessary to improve glycemic control and cardiovascular health,” Hu said.
“You can have a healthy Mediterranean diet, or a moderate-carbohydrate diet, or a very healthy vegetarian diet. There are different options for people with different dietary preferences.”
