Trans fatty acids (TFA) are still prevalent in U.S. supermarkets across a variety of common brand name foods, according to a new study.

The study, which analyzed trends in fatty acid content in common foods between 2007 and 2011, found that although some manufacturers have reduced TFA in their products, the scope of that reduction is unknown.

Other questions that remain include whether TFA reductions have varied by food type and by manufacturer.

In 2007, researchers identified 360 brand name products in major U.S. supermarkets that contained 0.5 g TFA or more per serving. The researchers re-examined those products again in 2008, 2010, and 2011.

The American Heart Association recommends no more than 2 g of trans fat per day, given a 2,000 calorie diet. This leaves virtually no room in the diet for eating industrially-manufactured trans fat.

The study also tracked hydrogenated vegetable oil content in 2011.

Of those products investigated in the study, researchers tracked changes in TFA content for the 270 products sold in all years between 2007 and 2011. The researchers found that by 2011, 66 percent of the products (178) had reduced TFA. The study also found that 82 percent of reformulated products - 146 out of 178 - had reduced TFA levels to below 0.5 g per serving, although half of those products still contained partially-hydrogenated vegetable oils.

Overall, the average of the 270 products decreased from 1.9 g to 0.9 g per serving.

TFAs are monosaturated or polysaturated fats that have been shown to increase risk for coronary heart disease, by increasing LDL cholesterol and lowering "good" HDL cholesterol.

Trans fats also increase likelihood of stroke, and are linked to higher risk of developing type-2 diabetes, according to the American Heart Association (AHA).

Small amounts of TFA occur naturally in meats and dairy products, but in modern American diets, the source of most TFA is industrially-produced partially-hydrogenated vegetable oils (PHVO). The partial hydrogenation of these oils is a commercially valuable feature, as it allows for the vegetable oils to be semi-solid at room temperature.

The reductions in TFA are slowing down, according to the study. However, overall, partially-hydrogenated vegetable oil use is still decreasing in the United States.

Trans fats can still be found in many foods, especially fried foods like French fries, doughnuts, and baked goods including pastries, pies, biscuits, pizza, crackers, and cookies. Trans fatty acids are also common in stick margarines and shortenings.

To stay within the daily recommended limits of trans fatty acids, the AHA recommends reading the nutrition facts panel on foods bought at the store. When at restaurants, ask in what kind of oil the food is cooked.

Source: Otite FO, Jacobson MF, Dahmubed A, Mozaffarian D. Trends in Trans Fatty Acids Reformulations of US Supermarket and Brand-Name Foods From 2007 Through 2011. Preventing Chronic Disease. 2013.