People who lost weight by following one of three diets in a randomized trial overtwo years also showed significant regression of carotid artery disease by ultrasound [1]. The changes appeared tobe largely mediated by reductions in blood pressure associated with the weight loss, according to the authors of a subgroup analysis from the Dietary Intervention Randomized Controlled Trial (DIRECT).

The carotid changes and their relationship to reduced blood pressure were independent of which diet a patient followed: low fat, Mediterranean, or low carbohydrate. In the trial’s primary analysis, published in 2008 [2], the three diets were equally effective at promoting weight loss. The population had consisted of 322 overweight or obese people aged 45 to 65 or adults of any age with type 2 diabetes or established coronary heart disease.

The current analysis covered the 140 participants who had evaluable baseline and follow-up carotid ultrasound scans; they didn’t otherwise differ substantially from the overall group, according to Dr Iris Shai (Ben Gurion University of the Negev, Beer-Sheva, Israel) and associates in their report published online March 1, 2010 in Circulation.

Importantly, carotid disease severity was tracked by both conventional carotid ultrasound of intima-media thickness (IMT) and the less established technique of carotid three-dimensional ultrasound imaging of “vessel-wall volume” throughout a defined carotid segment.

Over the two years of diet intervention, regardless of diet group, vessel-wall volumes diminished by 4.9% (p<0.001) while mean IMT improved by 1.1% (p=0.18).

“The standard for this kind of work is IMT, which is a single dimension. It’s a good measure, it’s predictive, but when you look at volume, in three dimensions, you get an enormous improvement in precision,” according to Dr Meir J Stampfer (Brigham and Women’s Hospital and Harvard School of Public Health, Boston, MA), primary author of the report. “It gives you much more statistical power for small changes that you might not otherwise pick up,” he told heartwire .

The volumetric ultrasound technique takes in “the entire vessel wall,” which Stampfer described as the combination of atherosclerosis and vascular muscle mass. But the relative contributions of reduced atherosclerosis or beneficial vascular-muscle remodeling to the observed diet-related regression seen in the volumetric analysis is unknown, Stampfer said. “It’s a limitation of the study.”

Independently commenting on the analysis for heartwire , Dr Victor G Davila-Roman (Washington University, St Louis, MO) observed that the volumetric ultrasound technique isn’t widely used. But assuming that its measurements “are accurate and reproducible, this would represent an improved way of assessing both atherosclerotic plaque and nonplaque volume noninvasively and would be an improvement over the current two-dimensional ultrasound method to assess carotid IMT, in which only the nonplaque thickness is assessed.

“The three-dimensional volumetric method allows comparison of before- and after-intervention measurements that represent regression of both atheromatous plaque and nonplaque regions,” Davila-Roman said. “The current thinking is that most of the regression would occur in the atherosclerotic plaque volume, particularly for those who have more extensive plaques.”

The 95 patients who showed carotid disease regression by the volumetric method, compared with the 45 showing disease progression, had a higher baseline vessel-wall thickness (p<0.001), lost more weight over the two years (p=0.03), and showed a deeper drop in systolic blood pressure (p=0.009). There were no significant differences between those groups in age, sex, statin use, baseline body-mass index, or prevalence of diabetes.

In multivariate analysis, a decrease in systolic blood pressure after two years of dietary intervention was the only variable to emerge as an independent predictor of regression, which it did regardless of whether it was gauged by the volumetric method (p=0.01) or standard IMT measurement (p=0.008).

Davila-Roman observed that many of the variables measured in the study are linked to each other and often change together. “The three diet interventions resulted in weight loss but also resulted in blood-pressure reductions and improvements in lipid levels,” he said. “Although the statistical analysis identified blood-pressure reduction as the most significant predictor of carotid artery volume regression, it is hard to say that it was only blood-pressure reduction that caused the regression.”

Of weight loss and blood pressure, only weight loss showed the significant independent association with regression, Stampfer observed, but he acknowledged that weight loss reduces blood pressure and that, “to some degree,” both are independently related to carotid disease regression. “You can’t completely tease them apart, but it did seem that blood pressure was the driver.”