The meta-analysis also found current evidence does not support high consumption of polyunsaturated fats, such as omega-3 fatty acid or omega-6 fatty acid to reduce coronary heart disease.
“This analysis of existing data suggests there isn’t enough evidence to say that a diet rich in polyunsaturated fats but low in saturated fats reduces the risk of cardiovascular disease, but large- scale clinical studies are needed, as these researchers recommend, before making a conclusive judgment,” said Jeremy Pearson, Ph.D., associate medical director at the British Heart Foundation, which helped fund the study. “Alongside taking any necessary medication, the best way to stay heart healthy is to stop smoking, stay active and ensure our whole diet is healthy, and this means considering not only the fats in our diet but also our intake of salt, sugar and fruit and vegetables.”
The Univ. of Cambridge led the international research collaboration. Researchers analyzed data from 32 observational studies of fatty acids from dietary intake, 17 observational studies of fatty acid biomarkers, and 27 randomized, controlled trials of fatty acid supplementation.
In the observational studies, relative risks for coronary heart disease were 1.02 for saturated, 0.99 for monounsaturated, 0.93 for long-chain, omega-3 polyunsaturated, 1.01 for omega-6 polyunsaturated, and 1.16 for trans fatty acids when the top and bottom thirds of baseline dietary fatty acid intake were compared.
In the randomized, controlled trials, relative risks for coronary disease were 0.97 for alpha-linolenic (an omega-3 fatty acid), 0.94 for long-chain omega-3 polyunsaturated and 0.89 for omega-6 polyunsaturated fatty acid supplementations.
“These are interesting results that potentially stimulate new lines of scientific inquiry and encourage careful reappraisal of our current nutritional guidelines,” said Rajiv Chowdhury of the Univ. of Cambridge and lead author of the research. “Cardiovascular disease, in which the principal manifestation is coronary heart disease, remains the single leading cause of death and disability worldwide. In 2008, more than 17 million people died from a cardiovascular cause globally. With so many affected by this illness, it is critical to have appropriate prevention guidelines that are informed by the best available scientific evidence.”
The American Heart Association, Dallas, recommends limiting the amount of saturated fats to less than 7 percent of total daily calories. According to the association, eating foods that contain saturated fats raises the level of cholesterol in the blood, which increases the risk of heart disease and stroke.
According to the Dietary Guidelines for Americans 2010, people should consume less than 10 percent of calories from saturated fatty acids by replacing them with monounsaturated and polyunsaturated fatty acids.
“A strong body of evidence indicates that higher intake of most dietary saturated fatty acids is associated with higher levels of blood total cholesterol and low-density lipoprotein (LDL) cholesterol,” the guidelines said. “Higher total and L.D.L. cholesterol levels are risk factors for cardiovascular disease.”
Loders Croklaan, which has an office in Channahon, Ill., for much of this century has disputed the statement that intake of saturated fat is associated with heart disease risk. The company supplies palm oil, which may be as much as 50 percent saturated fat.
According to Loders Croklaan, controlled studies and epidemiological studies that measure trans fat have shown little effect from saturated fat on coronary heart disease. The link between saturated fat and heart disease, according to the company, came from older studies that did not measure trans fat. The older studies erroneously ascribed negative effects of “hidden” trans fat to saturated fats.
The company, citing such evidence as a Framingham Heart Study published in 1988, said the best simple test for predicting heart disease risk is the ratio of total cholesterol to HDL cholesterol. Saturated fats raise both HDL, or “good” cholesterol, and LDL, or “bad” cholesterol, and thus saturated fats have little effect on the ratio of total cholesterol to HDL cholesterol, according to Loders Croklaan.
Now, the meta-analysis in the Annals of Internal Medicine gives further credence to the statement that current evidence suggests saturated fats have little to no effect on heart disease risk.
Besides researchers from the University of Cambridge, other researchers came from the University of Oxford, the Imperial College London and the University of Bristol in the United Kingdom; Harvard School of Public Health in Boston; and Erasmus University Medical Center in Rotterdam, The Netherlands. Besides the British Heart Foundation, other funding came from the Medical Research Council, the Cambridge National Institute for Health Research Biomedical Research Centre, and Gates Cambridge.