The Experts Speak
Cardiovascular Disease and Trans Fatty Acids
Walter C. Willett, M.D.
Department of Nutrition
Harvard School of Public Health
655 Huntington Avenue
Boston, MA 02115, USA
"Trans Fatty Acids and Cardiovascular Disease-Epidemiological Data,"
Atheroscler Suppl. 2006 May;7(2):5-8. Epub 2006 May 19 46212 (12/2006)
Kirk Hamilton: Can you please share with us your educational background and current position?
Walter C. Willett: I am an M.D., M.P.H., and Doctorate of Public Health in Epidemiology from Harvard School of Public Health. I am currently Professor of Epidemiology and Nutrition at Harvard School of Public Health and Chair of the Department of Nutrition, and Professor of Medicine, Harvard Medical School.
KH: What is a trans fat? Are they 'man-made?' What is their history of use in modern day food production?
WCW: Trans fats, or trans fatty acids are made by the industrial process called partial hydrogenation. They were originally produced, starting over 100 years ago, to convert liquid oils into margarine and vegetable shortening. At first this was simply a convenience, but later these were promoted as heart healthy products. More recently, they are widely used in the fast food industry for deep frying and in commercially baked products.
KH: How is a trans fat harmful to cholesterol metabolism, and subsequently to cardiovascular risk? Is there another mechanism besides altering cholesterol metabolism on how trans fats effect cardiovascular disease?
WCW: Trans fats appear to be involved at several steps in cholesterol metabolism and to increase LDL cholesterol and decrease HDL cholesterol. Both of these changes increase the risk of cardiovascular disease. Also trans fats increase levels of CRP and other inflammatory factors, which also increase the risk of cardiovascular disease. Saturated fat only increases LDL cholesterol, thus trans fats are far worse than saturated fats.
KH: What is the epidemiological data on trans fat intake and the risk to coronary heart disease?
WCW: In large prospective studies trans fats are consistently and strongly related to the risk of coronary heart disease; much more strongly than saturated fat.
KH: Is the consumption of trans fats a greater risk to coronary heart disease than saturated fat consumption, or to the risk of coronary heart disease by effecting HDL or LDL cholesterol levels?
WCW: Yes, trans fats have about twice the adverse effect on the LDL/HDL ratio as do saturated fats. Because of this and their other adverse effects, they are much more strongly related to heart disease than is saturated fat. We estimate that about 20 to 25% of coronary heart disease could be prevented by the elimination of trans fat from the partial hydrogenation of liquid vegetable oils.
KH: How important is the elimination of trans fats from the American diet and the incidence of coronary heart disease?
WCW: Elimination of trans fats is one of the most important and cost effective ways to reduce the incidence of CHD. Of course, we also need to work at smoking, being overweight, inactivity and other aspects of diet as no single change will sufficiently reduce the burden of this disease.
KH: In a perfect world what recommendations would you make to lower trans fatty intake? Can you somehow compare the risk:benefit ratio between the elimination of trans fats from the diet versus using statins for reducing cardiovascular disease risk?
WCW: Trans fats can be almost entirely eliminated by removing them from the "Generally Regarded As Safe (GRAS)" category by the FDA. Denmark has already done this and there is no reason we could not do so as well. From what we can see this would have almost as much benefit as putting the whole population on statins, and at extremely small cost. Trans fats are also related to risk of type 2 diabetes, and we estimate that 30 to 40 % of this disease might be avoided by replacing trans fats with polyunsaturated fat from non- hydrogenated vegetable oils.
KH: Do we have any hard data on intervention trials eliminating trans fats and cardiovascular risk?
WCW: No one has conducted a randomized trial of trans fat elimination on the risk of coronary heart disease, and I doubt that this would be possible. A recent 5-year study has been conducted in monkeys (presented at the ADA meeting by Kavenaugh et al.) in which trans fat increased body fat and insulin resistance.
KH: Do you have any other comments you would like to make on this interesting topic?
WCW: Martha-Claire Morris has reported results from a prospective epidemiologic study of dementia; trans fat intake was positively associated with risk, which is not surprising because dementia is related to vascular disease and generalized inflammation.