Artificial trans fats have become notorious for their undesirable effects on cholesterol levels. But a small clinical trial suggests that natural trans fats may not do the same damage.
When 61 healthy women followed a diet with a hefty dose of natural trans fats for four weeks, there were no changes in low-density lipoprotein cholesterol (LDL) and only small changes in high-density lipoprotein cholesterol (HDL).
Since food manufacturers have been removing artificial trans fats from their products, the natural variety is becoming our main source of dietary trans fat, said Dr Benoit Lamarche, a professor of food sciences and nutrition at Laval University in Quebec, Canada.
"The question iswhether this is a problem'" said Dr Lamarche, the senior researcher on the new paper. "This study suggests it's not."
Avoid trans fats and limit saturated fat
Among overweight women in the study, however, HDL levels declined by an average of 5%, although the mean level remained in the desirable range.
That's a potential concern, Dr Lamarche told Reuters Health. But on balance, he said, "we don't see what we see with industrial trans fats".
"The effects seem to be different, particularly with LDL," Dr Lamarche said.
Does that mean a healthy; normal-weight woman can eat all the meat and butter she wants? No, according to Dr Lamarche, whose study – funded by Dairy Farmers of Canada, Dairy Australia, Agriculture and Agri-Food Canada and the Canadian Dairy Commission – appeared online December 28 in the American Journal of Clinical Nutrition.
"This doesn't change the nutritional guidelines," he said, noting that the conventional advice is to avoid trans fats and limit saturated fat.
Trans fats boost women’s LDL
In this study, the researchers used a butter enriched with natural trans fats to substantially boost the women's intake over four weeks – equivalent to what you'd get if you consumed eight servings of dairy products in a day.
The women spent another four weeks using control butter with about one-third the amount of trans fat. All of the other diet components – from kilojoules to protein, to fibre and other types of fat – were kept the same between the two diets.
Dr David J Baer, a researcher at the US Department of Agriculture who wrote an editorial published with the study, told Reuters Health there are still unanswered questions
Only a handful of studies have tested the potential short-term effects of consuming natural trans fats, he said, and those studies have involved different doses of the fats, different approaches to adding them to the diet and different groups of people.
The only previous study that included women found that natural trans fats did boost women's LDL but not men's. However, Dr Baer pointed out, it used a higher daily allotment of the fats than the current study did.
CLA promotes fat loss
So for now, he added, "it's hard to make a blanket statement" about natural trans fats.
He noted that some researchers believe the point is moot. If you follow conventional wisdom and limit saturated fat, you'll end up with little natural trans fat in your diet.
On the other hand, some researchers are looking at ways to boost the concentration of one natural trans fat in dairy products – known as conjugated linoleum acid, or CLA. Animal research has suggested CLA can be heart-healthy and promote fat loss.
That could be done by changing how dairy cows are fed.
"If you want to produce a high-CLA product," Dr Baer said, "it will probably have more of the other trans fats too."
So that, he noted, is one additional reason for studying the potential health effects of natural trans fats.
(Amy Norton, Reuters Health, January 2012)