By David Liu PHD

Saturday March 3, 2012 (foodconsumer.org) -- Trans fat is known to increase risk for heart disease and heart attack, but a new study now found an association between dietary intake of trans fat and elevated risk for ischemic stroke in women.

The study found that overall total fat intake or intake of other types of fat was not associated with stroke risk.  But women eating the highest amount of trans fat were found at 39 percent increased risk for ischemic stroke, compared to those who did not as much.  Other confounders including lifestyle and dietary factors were already considered in the analysis.

Researchers found the association after analysing data from more than 87,000 women enrolled in the Women Health Initiative Study.   The study was reported in the March issue of the journal Annals of Neurology.

"Trans fats are well-recognized risk factors for heart disease and heart attack, and our study finds that they are a risk factor for ischemic stroke," said Ka He, co-author of the study, of the University of North Carolina at Chapel Hill. 

Trans fat is also known as partially hydrogenated vegetable oils.  Natural vegetable oils such as corn oil, soy bean oil and canola oil etc are in liquid form at room temperature and they are easy to be oxidized or become rancid.  Trans fat is in solid form because some portion of the liquid oil, which is highly unsaturated, is hydrogenated and the chemical structures of the fatty acids are changed. The problem with the partial hydrogenation process is that some fatty acids become trans-form, which we natural humans can't handle well.

In the United States, the Food and Drug Administration requires food processors to list trans fat on the nutrition fact label.   However, the agency allows the industry to claim zero trans fat when the total trans fat falls below 0.5 gram per serving. Because the serving size is determined by the manufacturer, virtually any processed food with trans fat can be labeled as Zero Trans Fat.

How can you determine whether a processed food contains trans fat?

Read the ingredient statement.  If it contains partially hydrogenated oil (cotton, soy or corn or whatever edible oil), then the food contains trans fat even  if the label claims zero trans fat.

Many food companies and restaurants have stopped using trans fat in all or some of their products.  McDonald's and Pizza Hat claim they do not use trans fat for their foods.  

Trans fat is associated with more than 100,000 deaths from heart disease each year in the United States, according to Harvard nutritionists and epidemiologists.  Ischemic stroke is a deadly condition in which blood vessels in the brain are blocked.

Trans fat is also linked to increased risk for diabetes.