• Higher Trans Fat Levels in Blood Associated With Elevated Risk of Heart Disease

Boston, MA — High consumption of trans fat, found mainly in partially hydrogenated vegetable oils and widely used by the food industry, has been linked to an increased risk of coronary heart disease (CHD). New York and Philadelphia have passed measures eliminating its use in restaurants, and other cities are considering similar bans.

A new study from the Harvard School of Public Health (HSPH) provides the strongest association to date between trans fat and heart disease. It found that women in the U.S. with the highest levels of trans fat in their blood had three times the risk of CHD as those with the lowest levels. The study was published online on March 26, 2007, and will appear in the April 10, 2007 print issue of Circulation: Journal of the American Heart Association.

“The strength of this study is that the amount of trans fatty acid levels was measured in blood samples from the study population. Because humans cannot synthesize trans fatty acids, the amount of trans fat in red blood cells is an excellent biomarker of trans fat intake,” said senior author Frank Hu, associate professor of nutrition and epidemiology at HSPH.

Clinical trials have shown that trans fatty acids increase LDL cholesterol and lower HDL cholesterol, making them the only class of fatty acids, which includes saturated fat, to have this dual effect. HDL (high-density lipoprotein) is considered a “good” cholesterol; LDL (low-density lipoprotein) a “bad” cholesterol…more details

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• Coronary Heart Disease and Trans Fat

The primary health risk identified for trans fat consumption is an elevated risk of coronary heart disease (CHD).^[36] A comprehensive review of studies of trans fats was published in 2006 in the New England Journal of Medicine reports a strong and reliable connection between trans fat consumption and CHD, concluding that “On a per-calorie basis, trans fats appear to increase the risk of CHD more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3 percent of total energy intake)”.^[4] This study estimates that between 30,000 and 100,000 cardiac deaths per year in the United States are attributable to the consumption of trans fats.^[37]

The major evidence for the effect of trans fat on CHD comes from the Nurses’ Health Study (NHS) — a cohort study that has been following 120,000 female nurses since its inception in 1976. In this study, Hu and colleagues analyzed data from 900 coronary events from the NHS population during 14 years of followup. He determined that a nurse’s CHD risk roughly doubled (relative risk of 1.94, CI: 1.43 to 2.61) for each 2% increase in trans fat calories consumed (instead of carbohydrate calories). By contrast, it takes more than a 15% increase in saturated fat calories (instead of carbohydrate calories) to produce a similar increase in risk. Eating non-trans unsaturated fats instead of carbohydrates reduces the risk of CHD rather than increasing it.^[38] Hu also reports on the benefits of reducing trans fat consumption. Replacing 2% of food energy from trans fat with non-trans unsaturated fats more than halves the risk of CHD (53%). By comparison, replacing a larger 5% of food energy from saturated fat with non-trans unsaturated fats reduces the risk of CHD by 43%.^[38]

Another study considered deaths due to CHD, with consumption of trans fats being linked to an increase in mortality, and consumption of polyunsaturated fats being linked to a decrease in mortality.^[36][39]

There are two accepted tests that measure an individual’s risk for coronary heart disease, both blood tests. The first considers ratios of two types of cholesterol, the other the amount of a cell-signalling cytokine called C-reactive protein. The ratio test is more accepted, while the cytokine test may be more powerful but is still being studied.^[36] The effect of trans fat consumption has been documented on each as follows:

• Cholesterol ratio: This ratio compares the levels of LDL (so-called “bad” cholesterol) to HDL (so-called “good” cholesterol). Trans fat behaves like saturated fat by raising the level of LDL, but unlike saturated fat it has the additional effect of decreasing levels of HDL. The net increase in LDL/HDL ratio with trans fat is approximately double that due to saturated fat.^[40] (Higher ratios are worse.) One randomized crossover study published in 2003 comparing the postprandial effect on blood lipids of (relatively) cis and trans fat rich meals showed that cholesteryl ester transfer (CET) was 28% higher after the trans meal than after the cis meal and that lipoprotein concentrations were enriched in apolipoprotein(a) after the trans meals.^[41]

• C-reactive protein (CRP): A study of over 700 nurses showed that those in the highest quartile of trans fat consumption had blood levels of CRP that were 73% higher than those in the lowest quartile.^[42]

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