NEW YORK—Cholesterol-raising trans fats may be disappearing from supermarket shelves and restaurants, but one type of fat taking their place may be no healthier, new research suggests.
Artificial trans fats are formed when food manufacturers add hydrogen to vegetable oil to make it solidify, in a process called hydrogenation. Partially hydrogenated oil boosts the stability of a food's flavor, as well as its shelf life, and the oils have long been a key ingredient in baked and fried foods.
Research has shown that trans fats in these oils may be even worse for heart health than the saturated fat found in foods like meat and butter. Not only do trans fats raise "bad" LDL cholesterol, as saturated fat does, but they also lower heart-healthy HDL cholesterol.
With trans fats so out of favor—New York City recently banned them from restaurants, and other cities may follow suit—the search for replacements is on.
However, one of those replacement fats—so-called interesterified fats—may carry their own health threats, according to a study published in the journal Nutrition & Metabolism. The interesterified oils may not only lower HDL levels but also cause a significant rise in blood sugar, researchers found.
The findings are a cause for concern, study co-author Dr. K. C. Hayes told Reuters Health, in part because the study volunteers used the interesterified fats for only 4 weeks. "Blood glucose went up quite precipitously," said Hayes, a professor of biology at Brandeis University in Waltham, Massachusetts.
The problem, he and his colleagues found, seems to be that interesterified fats change the body's levels of insulin, which regulates blood sugar.
The researchers arrived at their findings after having 30 healthy volunteers follow each of three diets for four weeks apiece. In each diet, participants got about 30 percent of their calories from fat, with the major source being either a natural saturated fat (palm oil), or partially hydrogenated soybean oil, or an interesterified soybean oil.
Compared with the palm oil, the interesterified fat increased volunteers' blood sugar by 20 percent, while also lowering their HDL.
Interesterified fats are already being used as a replacement for trans fats in commercial foods. "It's probably the number-one process to replace trans fats," Hayes noted. The current findings, he said, suggest that more research is needed before the fats become the new standard.
Hayes said consumers can find out whether their newly "trans-fat-free" crackers and cookies have interesterified fats by looking for "fully hydrogenated oil" on the package's ingredient list.
Source: Nutrition & Metabolism, online Jan. 15, 2007
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