The moderate-fat diet, in which half the fat was monounsaturated fat from peanuts and peanut oil, produced a 14 per cent reduction in cardiovascular disease risk. The low fat group experienced a 9 per cent improvement. Both the moderate and low fat diets were controlled so that all participants lost about the same amount of weight - approximately 2.4 to 2.7 pounds a week on average.
Dr Penny Kris-Etherton, distinguished professor of nutrition, said: "While the low-fat diet successfully reduced risk factors during the weight loss phase of the study, those factors rebounded during the maintenance phase."
The study, published in the February issue of the American Journal of Clinical Nutrition, involved 53 overweight or obese men and women with total cholesterol levels elevated above 200 at the start of the dieting.
The participants ate either a low-fat or moderate-fat diet designed to produce weight loss for six weeks and then similar diets designed for maintenance for four weeks. The foods were all provided by the researchers and provided 18 per cent of calories from fat in the low-fat diet or 33 per cent of calories from fat in the moderate fat diet.
Over the course of the study, the low-fat diet group experienced a 12 per cent decrease in HDL cholesterol but the moderate-fat diet group had no change. This indicates that a moderate-fat diet blunts the decrease in HDL cholesterol during weight loss.
In addition, after falling during the weight loss phase, triglycerides rose significantly during the maintenance phase for those on the low fat diet but not for those on the moderate fat diet. Elevated triglycerides are a cardiovascular risk factor.
"The findings of this current study are significant because they demonstrate that markedly lowering total fat intakes may have adverse consequences on reductions in the risk of CVD, even in response to weight loss," conclude the authors.
A recent study carried out by the nonprofit group RTI International and the Centers for Disease Control and Prevention found that obesity-related US medical costs reached $75 billion in 2003 with taxpayers paying up to $175 annually to foot the bill.
Obesity among teenagers has also risen dramatically with more than 2 million US adolescents becoming obese and another 1.5 million remaining obese as they grew into adulthood between 1996 and 2001. During the same period, only 271,000 dropped below weight levels considered excessive as they aged out of their teen years.
The World Health Organization has designated obesity as one of the most important public health threats because of the significant health impact of diseases associated with obesity such as cardiovascular disease.
The scale of the problem suggests that even with preventative measures being taken now, a large part of the US population will need weight loss treatment and help managing glucose levels in the future.