Mediterranean diet has advantages over keto in randomized study

There has long been debate about which low-carbohydrate diets — specifically, Mediterranean vs. ketogenic — offer the greatest health benefits to patients with prediabetes and type 2 diabetes, but a randomized study may offer an answer.

Researchers from Stanford University found that both diets improved blood glucose control — the study’s primary outcome — and both led to comparable weight loss in participants. However, unlike the Mediterranean diet, keto leads to elevated LDL cholesterol, lacks essential nutrients and is more difficult to maintain over time, giving the Mediterranean diet an edge.

Christopher Gardner, PhD, a nutrition scientist at Stanford, and colleagues conducted a randomized study of 33 adults with prediabetes or type 2 diabetes who followed both the Mediterranean diet and the keto diet for 12 weeks each in a random order. Both diets incorporate non-starchy vegetables and avoid added sugars and refined grains, but there are three key differences between them: the Mediterranean diet incorporates legumes, fruits and whole grains, whereas keto does not.

Results showed that HbA1c values improved after baseline on both diets, and the levels did not differ between them. The keto diet saw a greater decrease in triglycerides than the Mediterranean diet (percentage changes, –16% vs. –5%), but LDL cholesterol was higher for those on the keto diet (percentage changes, +10% vs. 5%) The potential harms of higher LDL associated with keto cannot be dismissed, the researchers said.

The diets also had similar results for weight loss (8% on the keto diet vs. 7% on the Mediterranean diet). HDL cholesterol increased 11% on the keto diet compared with 7% on the Mediterranean diet.

Results also showed that those on the keto diet had lower intake of fiber and three essential nutrients: folate, vitamin C and magnesium.

“These potential harms likely relate to avoiding legumes, fruits and whole, intact grains on the [keto diet], and temper enthusiasm for avoiding these food groups, which is consistently recommended by national and international public health organizations,” researchers wrote.

Additionally, at 12 weeks, participants were more likely to adhere to the Mediterranean diet than the keto diet, suggesting that the Mediterranean diet is more sustainable.

The researchers noted that the rise in LDL cholesterol, decrease in fiber intake and nutrient deficiencies associated with the keto diet are “concerning,” but longer-term studies are needed to fully understand the clinical implications.

“Collectively, these comparative outcomes do not support a benefit sufficient to justify avoiding legumes, whole fruits and whole, intact grains to achieve the metabolic state of ketosis,” the researchers said. However, “in a clinical setting, patients should be supported in choosing a dietary pattern that fits their needs and preferences. There should be less focus on promoting one particular diet approach as best; rather, clinicians should allow patients to make an informed choice to help them establish which approach is most suitable for them.”