A small study out of Italy is the latest of a growing list of non-randomized studies showing the benefits of low-carb diets.
Study authors enrolled 22 overweight adults without diabetes or other chronic disease. They were all instructed to eat a diet limiting carbohydrates. They were advised to eat yogurt, milk, nuts, and dark chocolate in limited amounts, as well as, limited vegetables and no more than two servings of fruit per day. They also took a whey protein supplement every day at breakfast. On average, their diets were 55% fat, 25% protein and 20% carbs.
After six weeks, the subjects lost 9 pounds (4 kilos), 2.5 inches (6 cm) from their waist, and 6.5 pounds (3 kilos) of fat mass. In addition, their blood pressure improved, their insulin levels dropped from 8.7 to 4.9 µIU/mL, their triglycerides from 99 mg/dl to 70, total cholesterol from 199 mg/dl to 182, and HOMA-IR from 1.8 to 1.1.
By now, these types of improvements seem routine, as study after study demonstrate these consistent benefits from low-carb diets. However, this study went further and also saw improvements in endothelial function measured by flow-mediated dilatation (FMD). This is a measurement of how "healthy" the blood vessels are based on how well they can enlarge with certain stimuli. After the low-carb intervention, they did better.
This finding is of particular interest as prior studies suggest fatty foods can worsen endothelial function. Of course, most of these are combined high-carb and high-fat diets. This research was one of the first to test endothelial function in a low-carb, higher-fat diet.
The subjects also saw an improvement in their carotid intima media thickness (CIMT), a measurement of the inner two layers of the carotid artery that is a predictor of cardiovascular risk. To be fair, the CIMT improvement was only 0.1 mm, which is not much. But the change was statistically significant after just six weeks.
As this is not a randomized study and there was no control group, it does not show that low-carb was better than any other diet (other than whatever they were eating before they entered the trial). But it does show that improving what you eat, and doing so with a focus on low carb, can improve many health markers including measures of vascular health.
We do need to temper our enthusiasm as we wait for higher quality data. It would be nice to have even longer-term outcomes, especially with the CIMT and endothelial function, to see if they remain significantly improved. And it would be even better to compare the results to a control group. Lastly, it would have been "cleaner" if they gotten their protein from natural food sources rather than a whey supplement.
We will certainly add this to the list of studies showing health benefits from low-carb nutrition. And at the same time, we call on all nutritional researchers to raise the bar for nutritional science moving forward.
Thanks for reading,
Bret Scher, MD FACC
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