In a corner: the medically renowned Mediterranean diet, a perennial favorite among nutritionists. The contender: The popular keto diet, known for limiting carbs to a few precious carbs per day.
Proponents of keto claim that the diet reduces appetite, melts belly fat and increases mental acuity, once a person is past the first few days of “keto flu,” a feeling of malaise, fatigue, and brain fog. At the very least, studies have shown a short-term improvement in blood sugar in people who also use keto.
Research has linked the Mediterranean diet to a reduced risk of diabetes, high cholesterol, dementia, memory loss, depression and breast cancer, as well as weight loss, stronger bones, a healthier heart and longer life.
A new controlled clinical trial conducted during the pandemic compared the two diets by asking 33 people with prediabetes or diabetes to follow both diets for three months in a row. During the first four weeks of each diet, participants received either healthy keto or Mediterranean meal deliveries and then self-followed their meal plans.
Researchers tracked participants’ weight, blood sugar (glucose), cardiovascular risk factors, and dietary adherence. What diet was still standing at the last bell?
“Both diets improved blood glucose control to the same extent, and both groups lost a similar amount of weight,” said leading nutrition researcher Dr. Walter Willett, a professor of epidemiology and nutrition at Harvard T.H. Chan School of Public Health and professor of medicine. at Harvard Medical School. He was not involved in the investigation.
However, when researchers examined the impact of the two diets on levels of blood fats that contribute to heart disease, the Mediterranean diet was the clear winner, according to the study published Friday in The American Journal of Clinical Nutrition.
The study tracked low-density lipoprotein, or LDL, known as the “bad” cholesterol, and triglycerides, another type of fat in the blood that also contributes to the hardening of the arteries.
“The keto diet significantly increased LDL cholesterol by 10%, while the Mediterranean diet lowered LDL cholesterol by 5%,” said Dr. Frank Hu, chair of the division 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,” said Hu.
While both diets reduced triglycerides, the keto diet did this more significantly, the study found. However, the reduction in triglycerides isn’t as significant as the rise in bad cholesterol, Hu said.
“High LDL cholesterol is a much more potent and important risk factor for cardiovascular disease than triglycerides,” he said. “So while both sides were quite effective at short-term glycemic control, I think the main issue is the potential long-term effects of keto on cardiovascular disease.”
Keto achieves rapid weight loss, proponents say, by putting people into ketosis, a state in which the body begins to burn stored fat for fuel. But to get to ketosis, carbohydrates are drastically reduced to 20 to 50 grams per day. (A cup of cooked rice is about 50 grams.) Eating extra carbohydrates will get you out of ketosis.
A typical American’s daily diet is 50% carbs, Hu said, so that’s off that intake to less than 50 grams is “an enormous reduction. That is difficult for people to sustain.”
People often think of keto as a “meat” diet and fill 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,” which 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. I haven’t tried 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 clinical and translational research at Stanford Diabetes Research Center.
The keto diet bans all grains, legumes, and fruits except for a handful of berries. However, the Mediterranean diet emphasizes packing 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 set up 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 rise in bad cholesterol, people in the keto phase had “reduced intakes of thiamine, vitamins B6, C, D and E, and phosphorus,” as well as an “incredibly low amount of fiber,” said Dr. shivam. Joshi, a clinical assistant professor of medicine at New York University Grossman School of Medicine. He was not involved in the investigation.
“Whole grains and fruits have positive health benefits, and their exclusion from the keto group raises some long-term concern health implications,” Willett said. In addition, he said, “Many people find that sticking to a keto diet for a long time is difficult.”
Indeed, the study found that most people dropped the keto diet after the study ended.
“They had keto delivered to their home. They had a health educator who helped them,” Gardner said. “Yet boom! Most people stopped eating the keto diet almost immediately (when that portion of the study ended), while many of those on the Mediterranean diet still ate that way when the study was over.
What is the core message of the research?
“The main message for me is that severe restriction of some healthy carbohydrates is not necessary to improve glycemic control and cardiometabolic health,” Hu said.
“You can follow a healthy Mediterranean diet or a moderate carbohydrate diet or a very healthy vegetarian diet. There are several options for people with different food preferences.”