Their 14-year study of almost 46,000 men showed that those who consumed the most trans fats had a 23% higher risk of gallstone disease than those who ate the least amount of trans fats.
That's a "modest" increase, say the researchers, who included Chung-Jyi Tsai, MD, ScD, of the University of Kentucky Medical Center.
Gallstone disease is common in the U.S. and other Western countries, and it's increasingly a major cause of digestive illnesses that prompt hospitalization, say Tsai and colleagues. Gallstones occur in about 20% of women and 10% of men by the age of 60. The risk of having gallstones increases with age and obesity.
About Trans Fats
"There has been concern for years that high intake of trans-fatty acids could have adverse health effects because they are structurally similar to saturated fats and lack the essential metabolic activity of the parent compounds," write the researchers.
In other words, trans fats may be too much like artery-clogging saturated fats and too little like the original fats (vegetable oils) they're made from.
Trans fats also naturally occur in small amounts in some animal products, such as butter, milk, cheese, beef, and lamb, says the web site of the FDA's Center for Food Safety and Applied Nutrition (CFSAN).
Studies have been "inconclusive" about the impact of trans fats on blood lipid levels, say Tsai and colleagues. Some research has shown that trans fats can reduce HDL "good" cholesterol and increase LDL "bad" cholesterol, they say.
The CFSAN puts it more bluntly: "Trans fat behaves like saturated fat by raising LDL cholesterol that increases your risk of coronary heart disease."
LDL cholesterol is notorious for clogging arteries, raising the risk of heart attack and stroke. Research has shown that in Western countries, about 80% of gallstones are cholesterol stones, says Tsai's study.
The men in Tsai's study were all health professionals enrolled in a long-term health study. They completed questionnaires about their medical histories and the foods they ate in 1986 and every two years after that.
Data came from men who hadn't had a gallstone removed or gallstone disease before. When Tsai's team randomly checked the men's reports of gallstone removal or gallstone disease diagnosis, they found almost complete accuracy.
The modest increase in gallstone risk with high consumption of trans fats wasn't due to other factors, say the researchers.
They adjusted for age, body mass index (BMI), recent weight change, smoking, history of type 2 diabetes, alcohol and caffeine intake, dietary fiber, physical activity, other kinds of fats, and certain drugs.
Targeting Trans Fats
Most American adults eat 5.8 grams of trans fats per day, or 2.6% of their total daily calories. On average, they consume four to five times as much saturated fat, says the CFSAN.
"Saturated fat and trans fat raise LDL ('bad') cholesterol. Therefore, it is advisable to choose foods low in both saturated and trans fats as part of a healthful diet," says the CFSAN.
Keep in mind that all fats aren't bad and that the body needs a certain amount of fat to work properly.
Unsaturated fats (monounsaturated and polyunsaturated) are beneficial when consumed in moderation, says the CFSAN. Look for healthier fats in nuts, fish, and avocados, but don't overdo it -- calories still count.
Trans fats needn't be totally eliminated from the diet, says the CFSAN. That would require "extraordinary diet changes (e.g., elimination of foods such as dairy products and meats that contain trans fatty acids)," which could lead to shortfalls of some nutrients and create other health risks.