Keto and Mediterranean diets both help manage blood sugar, but keto may have more side effects, according to research

• A low-carb keto diet and Mediterranean diet can both help manage blood sugar, new study finds.
• Both diets are high in vegetables and low in sugar and processed grains, helping prevent blood sugar spikes.

A high-fat ketogenic diet and a high-fiber Mediterranean diet may be equally effective for balancing blood sugar levels, according to a study published May 31 in the American Journal of Clinical Nutrition.

Researchers from Stanford University looked at data from 33 adults with pre-diabetes or type 2 diabetes to see how two different 12-week diet programs might affect their blood sugar levels and other markers of health. The order of the diets was randomly assigned, and participants were told to eat as much as they liked on each.

On a well-formulated keto diet, participants were told to eat between 20-50 grams of carbohydrates per day, moderate amounts of protein, and at least three servings of vegetables.

The other option, a Mediterranean diet, was based on traditional eating habits in countries like Spain and Italy, with mostly plant foods, olive oil, and fatty fish, nuts, and seeds.

Both diets included plenty of non-starchy vegetables such as leafy greens, and limit added sugar and refined grains like white bread. The difference was that Mediterranean dieters also ate beans, fruit, and whole grains, while keto dieters largely excluded those foods to keep their overall carb intake low.

The researchers found participants had similarly improved blood sugar levels after both diets, compared to before the study, and also lost a small amount of weight. The findings suggest Mediterranean and keto are equally viable strategies for managing blood sugar in people with diabetes or prediabetes.

However, the keto diet may have some side effects, while the Mediterranean diet may be easier to maintain over time, according to the researchers.

Keto dieters may have higher cholesterol, miss out on some nutrients, and have a harder time sticking to it long-term

While the keto diet improved participants blood sugar levels, it also raised cholesterol, which can be linked to higher risk of heart disease.

The high fat content of the keto diet — particularly if it's saturated fat from sources like butter, red meat, and dairy — has previously prompted concern from cardiologists and other medical experts who worry about the long-term risks of the keto diet. However, keto dieters had lower triglycerides, another type of fat linked to heart health issues, which may mitigate the risks of higher cholesterol, some evidence suggests.

Another potential problem with the keto diet was that participants were eating significantly less of certain nutrients, including vitamin C, folate, and magnesium.

Keto dieters also ate less fiber, a nutrient linked to healthy digestion and lower risk of chronic illness, while the Mediterranean diet significantly increased fiber intake.

Finally, researchers found the Mediterranean diet was significantly easier for participants to stick to. Keto may be difficult to sustain since dieters have to track carbohydrates closely and cut out a wide variety of foods, experts previously told Insider.

Overall, the findings suggest it may not be worth cutting out healthy high-carb foods on a keto diet, and a Mediterranean diet may work better for most people, although healthy low-carb diets may be a viable option, according to the researchers.

"There should be less focus on promoting one particular diet approach as best, and, rather, allow patients to make an informed choice to help them establish which approach is most suitable for them," the researchers wrote in the study.