Trans fats: We've been told that they're worse for our hearts than saturated
animal fats. Now, as consumers increasingly turn to food that's trans-fat-free
and manufacturers pull them from more and more processed foods, comes a twist.
Some trans fats, ones that exist naturally, may be good for you.
In a 4-month study at the University of Alberta presented in March at a
scientific meeting, obese rats fed a diet enriched with vaccenic acid -- a
naturally occurring trans fat found in milk and yogurt -- had significant
reductions in total cholesterol, LDL (or "bad") cholesterol and triglycerides.
The researchers reported that a key benefit of vaccenic acid is its ability to
reduce the production of chylomicrons -- small particles of fat, protein and
cholesterol formed in the gut that transport fats to various tissues of the
body.
Like humans, obese rats produce too many chylomicrons, which raises lipids in
the bloodstream. After 16 weeks of consuming vaccenic acid-enriched chow,
however, the levels of chylomicrons dropped by more than half.
It's not clear what this finding means for humans. First, the study was done in
rats -- the researchers say they're planning some human clinical trials with
vaccenic acid supplementation. Second, because the study diets were supplemented
with vaccenic acid, the amounts the rats ate relative to their body weight was
more than we would naturally eat in our usual diet.
The study is in line with other reports that natural trans fats have different
effects on the body than the industrially created ones.
Most of the trans fats we eat -- by far -- come from partially hydrogenated
vegetable oils, produced from liquid oils by industrial processing to create a
firmer fat. Others occur naturally in milk products, formed in the rumen (or
first stomach) of ruminant animals such as cows, goats, sheep and yaks when
they're fed a grass-rich diet.
Several studies of large populations have looked at the link between trans fatty
acid intake and risk of developing atherosclerosis, and all have shown that the
risk goes up only with the intake of "industrial" trans fatty acids, not the
natural ones. Several clinical trials -- in which people were fed special diets
for weeks or months -- have shown that manufactured trans fats raise LDL
cholesterol levels to the same degree as saturated fats, and also lead to lower
levels of the good, or HDL, cholesterol. It's been estimated that it takes only
about 12 grams of manmade trans fats to see this effect.
Trans-fat-free foods are big business, and today the majority of margarines,
cookies, snack cakes and chips are devoid of the stuff. The change was fueled by
the fact that, two years ago, it became law that food labels disclose industrial
trans fat content.
Even if all the partially hydrogenated vegetable oil disappeared from our foods,
we'd still consume about 1% to 5% of our calories from naturally occurring trans
fatty acids, mostly vaccenic acid.
At this point, it's not known how much vaccenic acid we'd need to consume to
reap benefits. But in the meantime, anyone wanting to increase their
natural-trans-fat intake might want to develop a taste for exotic cheese.
A study published in February in the Journal of Agriculture and Food Chemistry
reported that yak cheese, from animals grazing in alpine grassland, contains
more than four times the vaccenic acid of conventional cheddar cheese from
grain-fed dairy cows. (The study didn't investigate the levels in cheese from
grass-fed cattle.) It also contains three times more beneficial omega-3 fatty
acids. The authors conclude that a daily serving of 3 ounces of yak cheese might
promote health.
Yak cheese isn't easy to find -- but the bottom line seems to be that the fatty
acid composition of milk, cheese and yogurt from grass-fed animals may be more
healthful than we knew -- and perhaps, when the clinical trials are done,
vaccenic acid-rich milkfat may join the ranks of other healthful fats along with
those found in fish oil and nuts.
Cheese as a new, heart-positive snack? Just make sure you put it on a
whole-grain, trans-fat-free cracker.
Susan Bowerman is a registered dietitian and assistant director of the UCLA
Center for Human Nutrition.
