Food labels now list the amount of trans fat in foods. Consumers, however, need to develop some strategies to use this new information effectively.
The amount of trans fat per serving is listed on food labels underneath total fat, along with other types of fat, like saturated, polyunsaturated or monounsaturated. Although trans fat occurs naturally in some animal fat, most trans fats in the American diet come from partially hydrogenated oils. These are vegetable oils that have hydrogen forced into their chemical structure to give them a longer shelf life before spoiling. Because hydrogenated oils harden, they can be used in margarine or shortening. Almost a third of the fat in these products is trans fat.
Many consumers are aware that trans fat is unhealthy, but researchers don't yet agree on what amount is safe. There is no recommended limit or Daily Value (DV) for trans fat. For now, the message from nutrition experts is to get as little as you can while eating a balanced diet. You shouldn't try to eat zero trans fat, because you would have to avoid foods that provide healthful nutrients and only trace amounts of trans fat.
In some ways, trans fat has the same effect as saturated fat. Trans fat raises blood levels of LDL ("bad") cholesterol just like saturated fat. Although some researchers suggest that trans fat reduces good ("HDL") cholesterol, supporting evidence is inconsistent. Both saturated fat and trans fat may promote cancer development, too. But there is insufficient evidence to draw that conclusion yet.
When you try to reduce trans fat in your diet, you should consider both the amount of trans fat and saturated fat in your food choices. The federal government estimates that adult Americans consume on average about 5.8 grams of trans fat a day (about 2.6 percent of our calories). We consume four to five times as much saturated fat.
One simple strategy to lower your consumption of trans fat and saturated fat is to add the amounts listed for both on one product and compare that total against the totals of other products. You can even compare this total to the DV for saturated fat to see roughly whether it's high or low.
Comparing this total to a benchmark designed for saturated fat alone may seem too strict. But the DV for saturated fat is high for two reasons. It overestimates the amount needed by people who should have less than 1,800 calories per day because they are sedentary or overweight. It also overestimates how much the average person with high blood cholesterol should have. Their saturated fat should be below seven percent of their calorie total.
Checking the combined total of saturated and trans fat is an important health strategy because food manufacturers are experimenting with a wide range of new fats to replace partially hydrogenated oils. Some of these oils may reduce trans fat, but since they contain higher levels of saturated fat, there is no overall improvement.
The old suggestion to check the list of ingredients for partially hydrogenated oils to avoid trans fat is now less accurate advice than before and unnecessary. Plant breeding techniques have developed variations on common oils that contain fewer polyunsaturated fats, which require less hydrogenation to remain stable. Other fats may be blends of oils with varying characteristics. Since trace amounts of partially hydrogenated oils may be used to stabilize a product, don't rule out a food simply because you see a hydrogenated oil listed.
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If there is less than 0.5 grams of trans fat in a standard serving of a product, the label can declare that the trans fat content is zero, or the product is "not a significant source." But remember, if you eat three times the serving size of one of these products, you could get up to 1.4 grams of trans fat, an amount you may not want. Even when you select healthier food choices, don't forget that portion size matters.