June 1, 2011 -- Low-carbohydrate diets that require patients to fill up on fats won't lead to harder arteries, researchers say -- at least not in the short-term.
Those who lost 10 pounds after curbing their carb intake had no differences in arterial stiffness than those on a more traditional, low-fat diet, Dr. Kerry Stewart of Johns Hopkins and colleagues reported at the American College of Sports Medicine meeting in Denver.
"Losing weight may be more important to [arterial] health than the diet you're on," Stewart told MedPage Today.
Some researchers have raised concerns that replacing carbs with fats may have adverse effects on blood vessels, especially since promoting consumption of fats runs "counter to what the public has been told [about reducing fat intake] for the last 20 or so years," Stewart said.
Yet studies have shown that a low-carb diet can have positive effects on blood pressure, cholesterol, and other parameters that may reduce the risk of the artery disease atherosclerosis and subsequent heart disease.
So to assess what the diets are actually doing to patients' arteries, Stewart and colleagues enrolled 55 overweight or obese but healthy patients ages 30 to 65 in a lifestyle modification program. None had heart disease or other markers of cardiovascular risk at enrollment.
In addition to a supervised exercise program -- an hour-long regimen three days per week -- patients were randomized to either a low-carb or low-fat diet for six months. The researchers monitored arterial stiffness and other measures of blood vessel health.
For this analysis, the researchers had data on 23 of 28 patients who lost 10 pounds on the low-carb diet, and 23 of 27 who did so on the traditional diet. Those on the low-carb diet lost the 10 pounds sooner than the low-fat group did -- just 45 days instead of 70 days.
There were no changes in arterial stiffness or endothelial function in either diet group, and that didn't change after the results were adjusted for the time it took to shed 10 pounds, Stewart said.
"My theory is that if people can achieve weight loss, it will benefit vasculature in every other system of body," he told MedPage Today. "Weight loss, in the long run, will count more than the specific content of the diet."
Nor were there any acute effects on vascular function after a lone high-fat meal, the researchers found. In a companion study, 66 patients had no changes in endothelial function after eating a 900-calorie, 50-grams-of-fat meal from McDonald's. In fact, arterial stiffness significantly improved by 16 percent after that feast, the researchers found.
"It really seemed to make the arteries relax more, but we're not entirely sure how," Stewart said. "We'll have to look more deeply into that."
Some researchers contacted for outside comment said longer-term follow up may be needed to confirm those benefits. And analyses of the diet study that include the type of fats eaten would be helpful, they said.
"It would be nice to know what the fat consisted of, as some may be safer than others -- i.e. monounsaturated fats and omega-3 fatty acids and even polyunsaturated fats would be better than saturated fats," said Dr. Carl Lavie of the University of Queensland in New Orleans, who was not involved in the study.
Stewart said that upcoming analyses will break down the type of fats consumed, and that the dieticians involved in the study advised patients to stick to these healthier fats.
He added that the work should help allay physicians' concerns about recommending a low-carbohydrate diet -- something the medical community has largely been reluctant to do, he said.