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More Bad News About Donuts, French Fries,
and Cereals; Crackers Too

'Bad' Fats Found in Processed Foods Linked to Diabetes Risk

By Salynn Boyles, WebMD

June 8, 2001: —  Want to reduce your risk of diabetes? A new study suggests it is possible if you throw out the stick of margarine and processed baked goods. And forget about fried fast foods.

Fats known as trans fatty acids, commonly seen in these foods, already have been linked to heart disease and high cholesterol. Now a study from the Harvard School of Public Health suggests that limiting their consumption also can greatly lower diabetes risk. The research is reported in the June issue of American Journal of Clinical Nutrition.

But not all fats are created equal, and the Harvard researchers found that consumption of polyunsaturated fat, found in many liquid vegetable oils, actually appeared to be protective against diabetes. The researchers suggest that replacing trans fats in the diet with polyunsaturated fats can reduce the risk of diabetes by as much as 40%.

"This is the first study to show a link between trans fatty acid consumption and type 2 diabetes," study author Frank Hu, MD, PhD, tells WebMD. "We think this is a very important finding because the incidence of diabetes is increasing dramatically in the United States and worldwide."

Trans fats are formed when liquid fats are hydrogenated, or partially hydrogenated, to make them solid at room temperature. They are routinely used in commercially sold crackers, baked goods, cereals, and breads because they increase the shelf life of the products. Most restaurants also deep-fry foods in the oils.

The average American eats approximately 5 grams of trans fatty acids per day. That translates into about 7.4% of total daily fat consumed.

In this research, Hu and colleagues analyzed data from more than 80,000 women taking part in the Harvard School of Public Health's Nurses' Health Study. All the women were aged 34-59 when the study began in 1980, and none had heart disease, cancer, stroke, diabetes, or high cholesterol. The women were followed for the next 14 years, during which time they routinely answered questions about lifestyle and diet.

During the study period, just over 2,500 of the women were diagnosed with diabetes. The researchers found that total fat intake compared with calories from carbohydrates was not associated with diabetes incidence in these women. They also found no significant link between diabetes and the intake of saturated fats, which are found largely in animal and dairy products, or between diabetes and monounsaturated fats, which are found in olive, canola, and peanut oils. But a significant increase in diabetes risk was associated with consumption of trans fats.

Animal [saturated] fats have been perceived as the most dangerous fats, but, ironically, the hardened vegetable oils appear to be more dangerous than saturated fats," Hu says. "Five years ago, even in the scientific community, there was a lot of skepticism about the adverse effect of trans fats, but the data have been very convincing."

So how do you know if the processed foods you are eating contain trans fatty acid?

Currently, fats are not listed separately on nutrition labels, but the FDA has proposed that they be. Mandatory labeling of trans fatty acid content is a top priority at the FDA, according to a spokesman, and may be in place by the end of the year. In the meantime, look for the words, "hydrogenated oil" or "partially hydrogenated oil" in the ingredients list of processed baked goods, and stay away from deep-fried foods like French fries when eating out.

"There are a lot of hidden trans fats," Charleston, S.C.-based dietitian Jeannette Jordan, MS, RD, tells WebMD. "We know it is probably not possible for people to eliminate trans fats, but they can limit their consumption by reading food labels and being aware of where these fats are. There are simple things you can do too, like baking at home where you can control the type of fat you use."

Hu and Harvard colleagues have published several major studies evaluating the health risks and benefits of different types of fats. In these studies, monounsaturated and polyunsaturated fats have routinely been shown to be "the good guys" and saturated- and trans fats "the bad guys," he says.

"In the past, government guidelines talked about the benefits of a low-fat diet without distinguishing good fat from bad fat, and I think that is scientifically wrong," Hu says. "I think our research has revolutionized the idea that not all fats have to be avoided. Some fats are bad, but others are good, and we should use the good fats to replace the bad ones, rather than just reducing total fat."

Still, Jordan warns this message shouldn't be taken as a license to abandon attempts to limit calories from fat. In other words, you can't drown that salad in olive oil or deep-fry everything in soybean oil just because they are among the good fats.

"The thing you have to remember is that all fats, no matter what kind they are, have the same number of calories per gram," she says. "We can't abandon limiting overall fat consumption, because obesity is strongly linked to both diabetes and heart disease."