Keto vs. Mediterranean diet: which is better for blood sugar control?

A new study from Drs. Christopher Gardner, Lucia Aronica, and colleagues concludes that a whole foods keto diet and “Mediterranean Plus” diet both equally lower blood sugar in people with diabetes and prediabetes. However, they also caution that the keto diet “dangerously” raises LDL and may lead to nutrient deficiencies. 

The study was recently published in the American Journal of Clinical Nutrition, but the authors’  conclusions may not hold up upon closer inspection. 

The researchers randomly assigned 33 adults with type 2 diabetes or prediabetes to 12 weeks  on one of two diets. The first was a whole foods keto diet — with daily 20 to 50 grams of carbs, 1.5 grams/kilo of protein, at least three servings of non-starchy vegetables, and the remainder from fat. The second diet was what they called a “Mediterranean Plus” diet based on the Mediterranean pyramid but with no added sugar or refined grains. Both diets discouraged processed foods and encouraged whole foods. After the 12 weeks, the 33 subjects crossed over to the other diet. 

Interestingly, both groups ate about 300 calories less than their baseline diet. So, both diets proved to be higher-satiety diets (meaning participants felt fuller for fewer calories).

The authors reported that the primary outcome, HbA1c (a measure of blood sugar), was not significantly different between the groups, decreasing by 9% in the keto diet and 7% in the Med Plus diet. 

However, those on the keto diet successfully reduced their diabetes medications more than those on the Med Plus diet. Therefore, the keto diet showed better HbA1c reduction when accounting for the difference in medications. In addition, continuous glucose monitoring (CGM) data revealed that the keto diet led to a greater reduction in average glucose and more time spent in the normal blood glucose range than the Med Plus diet.

One conclusion is clear: both diets were improvements from the baseline diet. They both led to improved blood sugar, weight loss, and satiety.

But what about the concerns? The authors reported that LDL “dangerously” rose 10% on the keto diet. But was it really a dangerous change? Triglycerides went down on the keto diet, as we would expect. And as we saw in 2018 with the Virta Health trial, on average, LDL went up 10%. However, the calculated cardiac risk score went down 12%. 

How could that be? In the Virta study, other blood lipid markers improved: Apo B (a better measurement than LDL for predicting heart risk) didn’t change, and small LDL particles decreased, VLDL decreased, and the TG:HDL ratio decreased. 

The current trial from Gardner and colleagues didn’t report Apo B, small LDL, or VLDL. Therefore, they assume any rise in LDL must be dangerous. However, given the Virta Health data, at a minimum, we should likely conclude that we need more data before assuming harm. 

The other area of concern, the authors state, is the decreased intake of thiamine, folate, and vitamin C. But consuming less doesn’t mean being deficient long term. And it’s unclear if this has any clinical implication. So, again, the conclusion should likely be that we need more data rather than an assumption of harm.

So, what can we conclude from the study?

• Both keto and Med Plus improve blood sugar, with keto being slightly better
• Both keto and Med Plus help reduce caloric intake and are therefore higher-satiety diets

Sounds like a good place to start!