This conclusion, based on animal studies by researchers at Wake Forest University School of Medicine, was presented Monday at the 66th annual Scientific Sessions of the American Diabetes Association (ADA) in Washington, DC.

Trans fats are found in vegetable shortenings, margarines, crackers, cookies, snack foods, and other foods made with, or fried in, partially hydrogenated oils, according to the Food and Drug Administration (FDA). Trans fat is formed when food manufacturers add hydrogen to liquid oils, which turns them into solid fats like shortening and hard margarine.

Trans Fats Trigger Weight Redistribution

Consumption of saturated fat, trans fat, and dietary cholesterol raises low-density lipoprotein (LDL), or "bad" cholesterol, levels, which increases the risk of coronary artery disease, the FDA warns.

"Diets rich in trans fat cause a redistribution of fat tissue into the abdomen and lead to a higher body weight even when the total dietary calories are controlled," said Lawrence L. Rudel, PhD, professor of pathology and biochemistry and head of the Lipid Sciences Research Program at Wake Forest.

Over the six-year course of the study, male monkeys fed a western-style diet that contained trans fats had a 7.2 percent increase in body weight, compared to a 1.8 percent increase in monkeys that ate monounsaturated fats such as olive oil, said Kylie Kavanagh, DVM, in presenting the findings to the ADA.

All that extra weight went to the abdomen -- and some other body fat was redistributed to the abdomen. The monkeys on the diet containing trans fats had dramatically more abdominal fat than the monkeys on the monounsaturated fat, computed tomography (CT) scans showed.

The monkeys on the trans fat diet "deposited 30 percent more fat in their abdomen," said Kavanagh.

Same Calories, Greater Weight Gain

All of the monkeys consumed the same amount of daily calories, with 35 percent of the calories coming from fat. The amount of calories they got should only have been enough to maintain their weight, not increase it, Rudel pointed out. "We believed they couldn't get obese because we did not give them enough calories to get fat."

One group of monkeys got 8 percent of their calories from trans fat while the other group received those calories as monounsaturated fat. The amount of trans fat iin the monkeys' diet was comparable to the amount consumed by people who eat a lot of fried food, the researchers said.