Trans fatty acids (trans fats) have gained quite a reputation. Do they deserve their bad rap? The answer is yes. Their effect on cholesterol levels is worse than that of saturated fats. Identifying foods high in trans fats and reducing or even eliminating those foods from your diet is an important way to keep your heart healthy. In fact, it takes such a small amount of these so-called trans fats to negatively impact cardiovascular health that the American Heart Association recommends trans fats make up less than 1% of total calorie intake.
What Are Trans Fats?
The term “trans fat” refers to vegetable
(made up of mostly unsaturated fats) that have had hydrogen added to them. This process is known as
Partial hydrogenation of vegetable oils is done to make fats more solid at room temperature, to increase their shelf life by keeping their flavor stable over longer periods of time, and to guard against spoilage. Margarines, shortening, the oils used to cook fast food French fries, and commercial baked goods are all examples of foods that contain trans fatty acids.
The Harm of Trans Fats
Trans fats not only raise
LDL ("bad") cholesterol
levels (as saturated fats also do), they also lower levels of HDL cholesterol. Trans fat also increases blood triglyceride levels. Several studies have examined the effects of trans fats on cholesterol levels and heart disease risk.
Trans Fats and Cholesterol Levels
A study in the
New England Journal of Medicine
compared the effects on cholesterol levels of two different diets. One diet derived 20% of calories from fat sources containing varying amounts of trans fats (either soybean oil, semiliquid margarine, soft margarine, shortening, or stick margarine), and the other diet was enriched with butter. The researchers found that the use of soybean oil or semiliquid margarine (which contain the lowest amounts of trans fats) resulted in the most favorable effects on total and LDL cholesterol levels and ratios of total cholesterol to HDL cholesterol. The use of stick margarine (which contains the highest levels of trans fats) had the least favorable effects.
The researchers also found that trans fats lowered HDL cholesterol levels to the same degree that saturated fats raised HDL cholesterol levels. So, while both saturated fats and trans fats raise LDL levels to a similar degree, trans fats do the added damage of lowering levels of protective HDL cholesterol. Stick margarine lowered HDL cholesterol levels to a greater degree than sources containing less trans fats.
Studies also suggest that trans fats are associated with inflammation, which is a risk factor for CHD,
heart failure, and sudden death from heart failure. A few studies have examined the relationship between trans fat intake and the risk of developing
type 2 diabetes.
Another study showed that eating trans fat causes weight gain in the abdomen, more so than other types of fat. All fats have the same calories, but the chemical makeup of trans fat is such that it deposits fat in the abdomen. Increased girth in the abdomen is associated with higher risk of most diseases.
For now, it is clear that all it takes is a small amount of trans fat, just 1%-3% of total calorie intake, to negatively impact health—for someone consuming 2,000 calories a day this translates into two to seven grams of trans fat.
Food Labels and Trans Fats
Because of the strong evidence showing that trans fats increase the risk of heart disease, the US Food and Drug Administration (FDA) requires food manufacturers to list trans fat amounts on the
nutrition facts panel of the food label.
Under this rule, trans fat is listed as a separate line item under saturated fat. However, if a food contains less than 0.5 grams of trans fat per serving, food manufacturers may list it as containing 0 grams of trans fat. So, a food may contain trans fats in small amounts, but still be considered “trans-fat free.”
The only way to be sure that a food is completely free of trans fat is to carefully inspect the ingredient list for the phrases “partially hydrogenated” or “shortening." These terms indicate that the food contains trans fats. This also makes it important to pay attention to serving sizes, since eating just two servings of a food could boost the trans fat content to a higher level.
Which Foods Contain Trans Fats?
In addition to reading the Nutrition Facts panel, here are some ways for identifying foods that contain trans fats:
Partially hydrogenated oils is listed as an ingredient
Certain groups of foods tend to be high in trans fats, including:
Deep fried foods, such as doughnuts and French fries
Foods that sit on the shelf, but still stay fresh (eg, cookies, chips, crackers, baked goods)
Frozen foods, especially frozen meals and pizzas
Foods that are solid at room temperature when they should be liquid (eg, margarine that is solid, but made from oil)
Meat and dairy products (small amounts of trans fat are found naturally in these foods)
Since the FDA's rule went into effect, many food companies have eliminated trans fats from their products. But because food labels are only required on packaged foods, foods served at restaurants and bakeries are still likely to contain partially hydrogenated vegetable oils or shortening. Some cities in the US have banned restaurants from using trans fats. For example, restaurants in New York City are now trans-fat-free. Some large fast food companies, like McDonald's and Kentucky Fried Chicken, have also made the switch.
Margarine (particularly stick margarine) is another food high in trans fats. When it comes to margarine, the more solid it is, the more trans fat it contains. The following table compares the amount of total fat, saturated fat, and trans fat in butter and margarine.
Fat Per Serving of Butter or Margarine (grams/serving)
Adapted from: US Food and Drug Administration
Lowering How Much Trans Fat You Eat
Use the following strategies to cut down on your trans fat intake:
Eat less of the following foods:
Margarine (particularly stick margarine)—Use olive oil, canola oil, liquid, or trans-fat-free tub margarines instead.
Cookies, cakes, and pastries
Crackers, cereals, and snack foods containing partially hydrogenated vegetable oil
French fries and other fried foods
If you enjoy margarine on your morning toast, use tub margarine that contains no trans fat and is low in saturated fat and use a smaller amount.
Check the list of ingredients. If partially hydrogenated oils appear on the list, the food contains trans fats, even though it may be a very small amount.
Ascherio A, Hennekens CH, Buring JE, Master C, Stampfer MJ, Willett WC
. Trans-fatty acids intake and risk of myocardial infarction.
Board of Health votes to phase out artificial trans fat from New York City's restaurants. New York City Department of Health and Mental Hygiene website. Published December 2006. Available at:
http://www.nyc.gov/html/doh/html/pr2006/pr114-06.shtml. Accessed July 17, 2008.
Center for Food Safety and Applied Nutrition. Questions and answers about trans fat nutrition labeling. US Food and Drug Administration website. Available at:
http://www.cfsan.fda.gov/~dms/qatrans2.html. Accessed September 10, 2006.
Hu FB, Stampfer MJ, Mansonet JA, et al. Dietary fat intake and the risk of coronary heart disease in women.
N Engl J Med. 1997;337:1491-1499.
Lichtenstein AH, Ausman LM, Jalbert SM, et al. Effects of different forms of dietary hydrogenated fats on serum lipoprotein cholesterol levels.
N Engl J Med. 1999;340:1933-1940.
Lichtenstein AH, Appel L, Brands M, et al. Diet and lifestyle recommendations revision 2006. A scientific statement from the American Heart Association Nutrition Committee.
Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular diseases.
N Engl J Med.
Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a