Trans fats are commonly found in foods made using partially hydrogenated oils.
Researchers reviewed the findings of a series of six surveys carried out as part of the Minnesota Heart Survey, from 1980-2009. The surveys included data from over 12,000 adults aged 25-74 in the Minneapolis-St. Paul area.
Intake of both trans fat and saturated fats fell during this period but was still some distance away from the levels recommended as healthy by the American Heart Association (AHA).
"There's a downward trend in trans and saturated fat intake levels, but it's clear that we still have room for improvement," says Mary Ann Honors, lead author of the study published in the Journal of the American Heart Association.
Trans fats raise low-density lipoprotein (LDL, or "bad") cholesterol levels in the body and lower levels of high-density lipoprotein (HDL, or "good") cholesterol. They have been found to increase the risk of coronary heart disease - the number one cause of death in the US - along with stroke and type 2 diabetes.
The main source of trans fats in American food is in partially hydrogenated oils, created when hydrogen is added to vegetable oils in order to make them more solid. These trans fats are referred to as artificial trans fats. Partially hydrogenated oils are utilized as an inexpensive way to extend the shelf life of food and improve texture and flavor stability.
Fried, processed and commercially baked goods are the main sources of artificial trans fats. Cookies, doughnuts, pastries, pies, pizzas and sticks of margarine are all regularly made using partially hydrogenated oils.
The US Food and Drug Administration (FDA) state that there is no safe level of artificial trans fats consumption and so consumption should be kept as low as possible. The AHA recommend limiting trans fats to no more than 1% of total calories consumed.
According to the Centers for Disease Control and Prevention (CDC), avoiding artificial trans fats completely could prevent up to 20,000 heart attacks and 7,000 coronary heart disease deaths in the US every year.
Trans fat intake has decreased by about one third
The researchers found that trans fat intake had decreased by around 32% in men and 35% in women over the course of the study. However, men and women still consumed 1.9% and 1.7% of their daily calories, respectively, from trans fats - significantly higher than the AHA's recommended level.
Similarly, the intake of saturated fats dropped but levels were still much higher than what the AHA consider to be healthy. Men and women took 11.4% of their daily calories from saturated fats, whereas it is recommended that saturated fat consumption should be limited to just 5-6%.
Intake of omega-3 fatty acids was also measured and found to have not changed significantly over the last 3 decades. Omega-3 fatty acids are believed to reduce the risk of cardiovascular disease, yet the researchers found that the current level of intake is relatively low.
"To make your diet more in line with the recommendations," says Honors, "use the nutrition panel on food labels to choose foods with little or no trans fats." Caution is needed; the AHA advise that products can be listed as containing 0 grams of trans fats if they contain 0-0.5 g of trans fats per serving. Look out for partially hydrogenated oils in lists of ingredients.
Although the study participants were predominantly white men and women living in a small area of the country, the authors write that similarities between their study and levels of intake reported in national data suggest their findings may generalize well to the US population.
The authors state that future research is needed in order to determine public health strategies to reduce further the levels of trans and saturated fat intake. In the meantime, the CDC suggest that eating a balanced diet rich in fruits, vegetables, whole grains, lean sources of protein and low-fat or fat-free dairy products is the best way to avoid trans fat.
Medical News Today recently reported on a study finding a disparity in overall dietary quality between different socioeconomic, racial and ethnic groups, which continues to grow.