The study adds to the debate on diet types, following on from findings that a low-carbohydrate diet, like the once fashionable Atkins diet, may put followers at a higher risk of clogged arteries and heart attack in the long-term, and adversely affect the numbers of certain types of bacteria in the gut of obese men.
This recent study was published last month in Hypertension, was led by David Gutterman from the Medical College of Winsconsin, and written by Shane Phillips, from the University of Illinois.
This was a small study with only 20 participants, aged between 18 and 50 and with a body mass index ranging from 29 to 39, meaning they were classified as obese. The type of diet was randomly assigned to the participants.
"Low-carbohydrate diets are significantly higher in total grams of fat, protein, dietary cholesterol and saturated fats than are low-fat diets," said Phillips.
"While a low-carbohydrate diet may result in weight loss and improvement in blood pressure, similar to a low-fat diet, the higher fat content is ultimately more detrimental to heart health than is the low-fat diet suggested by the American Heart Association,"
Dieting to manage weight
Obesity is becoming an ever-growing problem. The World Health Organisation's (WHO) latest projections indicate that globally, in 2005, approximately 1.6bn adults were overweight and 400m were obese. In 2006, 30 per cent of European children were estimated to be overweight.
A Datamonitor survey found that around 65 per cent of Europeans and Americans made active attempts to eat healthier in 2005-2006. In his write-up of this scientific study, Phillips said it was estimated that in America, 45 per cent of women and 30 per cent of men opt for diets to lose weight.
According to the study's author, obesity is associated with impaired endothelial-dependent flow-mediated dilation, which is a precursor to hypertension and atherosclerosis.
Although dieting generally improves cardiovascular risk factors, Phillips said the direct effect of different dieting strategies on vascular endothelial function is not known, and so the purpose of the study was to investigate this.
Weight loss, flow-mediated dilation (a measure of blood flow), blood pressure and insulin and glucose levels in participants were measured every two weeks during a six week period.
The low-carbohydrate diet provided 20 grams of carbohydrates daily and was supplemented with protein and fat content according to the Atkins' diet recommendations. The low-fat diet provided 30 per cent of the calories as fat, and was modeled after the American Heart Association's recommendations.
Researchers found reduced flow-mediated dilation in the arm artery, an early indicator of cardiovascular disease (CVD), in participants who were on the low-carbohydrate diet.
On the other hand, flow-mediated dilation improved significantly in participants on the low-fat diet suggesting a healthier artery less prone to developing atherosclerosis.
Gutterman said: "The higher fat content of a low-carbohydrate diet may put dieters at an increased risk of atherosclerosis (hardening of the arteries) because low-carbohydrate diets often reduce protection of the endothelium, the thin layer of cells that line the blood vessels of the circulatory system.
"The reduced production from the endothelium of nitric oxide, a specific chemical, puts the vessel at higher risk of abnormal thickening, greater clotting potential, and cholesterol deposition, all part of the atherosclerosis process."
Low-carbohydrate diets were also found to have significantly less daily folic acid than low-fat diets. Folic acid is thought to help reduce the risk of heart disease.
Researchers said this protective effect results from the antioxidant property of folic acid and its ability to lower levels of homocysteine, a naturally occurring amino acid that can be dangerous at elevated levels.
However, because the effects of the two diets were only recorded on a small number of participants over a short period of time, further investigation would be required covering more varied demographics.
Voume 51, Pages 376-382
Title: "Benefit of Low-Fat over Low-carbohydrate Diet on Endothelial Health in Obesity"
Authors: Shane Phillips, Jason Jurva, Amjad Syed, Jacquelyn Kulinski, Joan Pleuss, Raymond Hoffman and David Gutterman