A 36-week study from Stanford University compared the benefits of two diets — a Mediterranean diet and a ketogenic diet — for treating 33 individuals with prediabetes or type 2 diabetes (American Journal of Clinical Nutrition, July 19, 2022). Both diets were based on eating lots of non-starchy foods that do not cause a high rise in blood sugar, and avoiding foods that cause a high rise in blood sugar such as sugar-added foods or drinks and foods made from flour (ground-up whole grains). The participants spent 12 weeks on one diet and then switched to the other diet for another 12 weeks, ending with 12 weeks of follow-up.
In this study, the main differences between the two diets were that legumes, fruits, and whole (unground) grains were avoided in the keto diet and included in the Mediterranean diet. The keto diet severely restricted all carbohydrates in beans, fruits, and whole grains, while the Mediterranean diet restricted only the sugary foods and drinks and refined carbohydrates that cause a high rise in blood sugar. The study found that both diets can help people control high blood sugar levels.
Levels of Hemoglobin A1c (a blood test that serves as a proxy for cell damage from high blood sugar) were the same on both diets and weight loss was essentially the same. Those on the keto diet had lower triglycerides, slightly higher LDL (bad) cholesterol levels and slightly lower HDL (good) cholesterol levels. Those on the keto diet also had lower essential nutrients (folate, vitamin C and magnesium) from avoiding legumes, fruits, and unground whole grains.
Description of Keto Diets
Ketogenic diets restrict carbohydrate intake to less than 25 to 50 grams per day, so a typical day has five percent of calories from carbohydrates, 75 percent from fats and 20 percent from protein. This causes your liver to produce large amounts of ketones to be used as a source of energy (JAMA, Jan 2020;323(4):386). Some doctors recommend ketogenic diets to help overweight diabetic patients lose weight, but that weight loss is not greater than that produced by other treatments for diabetes. Claims that keto diets help to treat cancer, dementia and Parkinson disease are not supported by adequate scientific studies. Reported side effects of keto diets include:
• fatigue during exercise
• feeling tired all the time
• increased hunger
• difficulty falling asleep at night
• muscle cramps
• constipation from lack of fiber
• nausea, feeling bloated
Restricting carbohydrates to less than five perccent of calories can cause a deficiency of antioxidant phytonutrients in fruits and vegetables (JAMA, 2018;319(3):215-217). Severely restricting all carbohydrates and replacing them mostly with fat is associated with increased risk for non-alcoholic fatty liver disease (JAMA Intern Med, published online July 15, 2019) that can lead to diabetes, heart attacks, strokes and liver and other cancers (Curr Opin Clin Nutr Metab Care, Jul 1, 2012;15(4):374–380). Keto diets can increase markers of cholesterol and inflammation, although they can lower triglycerides (Obesity (Silver Spring), June 2019;27(6):971-981). Any diet that restricts fruits, vegetables, whole grains and beans can harm you because these plant foods are rich sources of soluble fiber that is converted in your intestines to short chain fatty acids (SCFAs), which lower high cholesterol, high blood pressure, and high blood sugar. A deficiency of soluble fiber markedly increases risk for inflammation that can damage cells throughout your body.
In the conclusions of this study, the authors prefer the Mediterranean diet over the Keto diet because the key to lowering high blood sugar is to avoid all foods that cause a high rise in blood sugar after you eat them. Restricting carbohydrate foods that don’t cause a high rise in blood sugar, such as vegetables, legumes, some fruits and whole, intact grains, doesn’t offer any additional benefit and may be harmful as it deprives you of soluble fiber that has been shown to lower high cholesterol, blood sugar, insulin and inflammation. They also note that the Mediterranean diet is easier to follow.
I do not recommend ketogenic diets because:
• Keto diets usually involve restricting unrefined carbohydrates. There is a huge difference between unrefined and refined carbohydrates. Unrefined carbohydrates as are found in nature are almost always loaded with healthful soluble fiber and are associated with reduced risk for disease and increased life span. I do recommend restricting refined carbohydrates — sugared drinks and sugar-added foods, and foods made with flour.
• Keto diets encourage people to eat large amounts of red meats and processed meats, which I believe are unhealthful.
If you want to lose weight, I recommend Intermittent Fasting. To maintain a healthful weight, prevent disease and prolong your life, I recommend that you eat a wide variety of unrefined carbohydrates (vegetables, fruits, whole grains, beans, nuts and other seeds), and try to exercise every day.