DALLAS, September 1 -- Eating a low-fat diet has been shown to reduce some risk factors associated with heart disease and stroke, but reducing fat in the diet to very low levels may not provide any additional benefit, according to a new statement from the American Heart Association.
The statement says there is not enough data to recommend very low fat diets as a strategy to reduce blood levels of total cholesterol, and in particular the "bad" cholesterol, LDL. According to the statement published in today's issue of Circulation: Journal of the American Heart Association, very low fat diets cannot be recommended to reduce body weight or the risk of death from heart disease on a population wide basis.
Very low fat diets contain no more than 15 percent of total calories from dietary fats. Current recommendations call for no more than 30 percent of total calories consumed daily to come from fat, with no more than 10 percent of the total derived from saturated fats, such as those that come from animals.
"Results from a few clinical trials have suggested that very low fat diets may be associated with reduced risks for cardiovascular disease, but there remain numerous unanswered questions that make population-wide recommendations of such diets premature," says Alice Lichtenstein, D.Sc., co-author of the statement, written on behalf of the AHA's Nutrition Committee. She is also an associate professor of nutrition at Tufts University.
"Very low fat diets, at least in the short term, tend to increase triglycerides and decrease 'good' cholesterol, or HDL, levels without yielding additional decreases in LDL levels."
Triglycerides are the chemical form in which most fat exists in food as well as in the body. An excess amount of triglycerides in the blood is linked to decreased levels of HDL cholesterol and the occurrence of heart disease in some people. Lichtenstein says very low fat diets have been, "consistently shown to increase the levels of triglycerides in the blood."
Lichtenstein points out that it is difficult to determine whether a very low fat diet alone was responsible for the decreases in risk factors reported in the population-based, interventional, and clinical studies that were analyzed.
"Most of the studies that examined very low fat diets also included other factors that can also decrease some of the risk factors often associated with cardiovascular diseases," she says. "For example, increased consumption of fruits, vegetables and whole grains as well as increased physical activity levels and weight loss can help raise HDL cholesterol and lower LDL cholesterol in some individuals.
"Therefore, it was hard to know whether the risk reduction in any given study was due to a synergy between a very low fat diet, increased physical activity, weight loss and increased consumption of fruits and vegetables, or any one of those factors alone," she adds.
Another important question is whether very low fat diets provide enough nutrients, such as vitamins and minerals. Individuals eating a very low fat diet appear to "make up" at least some, if not all, of the calories that would have been consumed as fat with simple and/or complex carbohydrates.
"A label touting fat-free or low-fat should not be the only criterion used when making dietary modifications aimed at reducing the total and saturated fat content of the diet," she says. "The level of vitamins and minerals as well as calories must also be taken into consideration."
The report states that very low fat diets may pose serious health risks for young children, pregnant women, the elderly and individuals with insulin dependent diabetes mellitus or elevated blood levels of triglycerides.
Sometimes referred to as the AHA Step I Diet, reduced total and saturated fat diets are a general guideline for the population as a whole to help reduce heart disease and stroke. Further reductions in saturated fat intake, to no more than 7 percent of total calories, characterizes the AHA Step II diet and is currently recommended as the starting point for dietary interventions for individuals at increased risk of coronary heart disease.
The AHA recommends a healthy eating plan containing a variety of foods, rich in fruits, vegetables, whole grains, low fat dairy products and lean meats. This is based on data that indicate a prudent diet, coupled with regular exercise for about 30 minutes a day and maintaining a healthy body weight, can help people reduce total cholesterol, LDL cholesterol and their overall risk from heart attack and stroke.
Linda Van Horn, Ph.D., R.D., of Northwestern University Medical School, is a co-author.