NEW YORK - Pregnant women who down trans fats from snack foods, fast food and other less-than-ideal fare may give birth to bigger babies, a new study suggests.
The study, of nearly 1,400 pregnant women, found that the higher a woman's intake of trans fats during the second trimester, the larger her newborn.
Exactly what the findings mean is uncertain. For one, they don't prove that trans fats, per se, boost fetal growth. And if they do, it's not clear how harmful that could be. Better growth in the womb could be a good thing, since it would lower the risk of low birthweight.
On the other hand, there are risks to having a larger-than-normal newborn, said lead researcher Juliana Cohen, of the Harvard School of Public Health in Boston.
Big babies may have to be delivered by C-section. And, Cohen, said, studies have found that they may have increased risks of diabetes and heart disease later in life.
Even though the effects of trans fats on fetal growth are unclear, they are already thought to be a health risk, Cohen noted.
"It's prudent to limit trans fats in your diet anyway," she said in an interview. "Pregnant women may want to think about how (the fats) could affect fetal growth as well."
Artificial trans fats are found in foods that contain partially hydrogenated oils -- including many baked and fried packaged foods like chips, crackers and cookies, as well as fast food. Trans fats are considered particularly unhealthy because they not only raise "bad" LDL cholesterol, but also lower heart-healthy HDL cholesterol.
Some meat and dairy products contain natural trans fats. But people get the bulk of their trans fat in the artificial form -- though, with all the bad publicity, food producers and some restaurants have been cutting back on trans fats.
The American Heart Association recommends that people get less than 1 per cent of their daily calories from trans fat. For someone who gets 2,000 calories a day, that would translate into fewer than 2 grams of trans fat.
The current findings, reported in the American Journal of Clinical Nutrition, are based on about 1,400 Boston-area women who gave birth between 1999 and 2002. The women completed dietary questionnaires during their first and second trimesters.
Overall, Cohen's team found that as women's intake of trans fats during the second trimester rose, their newborn's birth size also crept up.
The relationship held even after the researchers accounted for other factors, like pre-pregnancy body weight, income, education and calorie intake during pregnancy.
The researchers calculated that for every 1 per cent increase in trans fat as a replacement for carbohydrates in a woman's daily diet, her baby's fetal growth "Z score" inched up slightly.
The Z score takes into account a newborn's birthweight and the week of pregnancy during which the baby was born.
The Z-score effect linked to trans fats would be modest in real life, according to Cohen.
But, she said, the foods that contain trans fat are best limited for overall health -- though unfortunately, she added, they are also often the ones women "crave" during pregnancy.
In general, experts recommend reading nutrition labels to see if a product contains partially hydrogenated oils, and limiting processed foods in favour of "whole" foods like fruits and vegetables, whole grains, fish and lean meat.
They also advise opting for the "good," unsaturated fats found in sources like olive oil, fatty fish and nuts.