Although much-criticized trans fats raise levels of "bad"
cholesterol, they don't appear to have a lasting impact on blood
sugar levels, according to a U.S. study.
Researchers, writing in The American Journal of Clinical
Nutrition, found that both blood sugar and insulin, the hormone
that keeps blood sugar levels in check, were similar regardless
of how much trans fat people ate.
The link between trans fats and high cholesterol levels is
widely accepted, but there has been a lack of clarity on the
effect on blood sugar control, which is involved in diabetes.
"Although evidence from cohort studies has suggested that trans
fatty acid (TFA) consumption may be associated with insulin
resistance and diabetes, randomized placebo-controlled trials
have yielded conflicting results.
Trans fats, technically known as trans fatty acids, are found in
animal products and chemically processed vegetable oils.
Some cities and states have banned them in restaurants or
In five of the studies, the participants' blood sugar, insulin
and cholesterol levels were monitored for several weeks under a
diet of high trans fat consumption, and again for a few weeks
when the trans fats were substituted for other fats, such as
palm or soybean oil.
Two of the studies compared people who ate a diet that included
trans fats to others who ate a diet without trans fats.
There were no changes in blood sugar or insulin levels during
the times when people ate trans fats, compared to when they ate
the other fats.
However, the researchers found that during the trans fat-eating
weeks, "good" HDL cholesterol went down and "bad" LDL
cholesterol went up.
Pereira, who was not involved in the study, said it isn't
definitive proof that trans fats can't influence blood sugar
Although several weeks is enough time to see an effect on
cholesterol, he said, a potential impact on metabolism might not
show up until later.