Novel research conducted in Malaysia and at
Brandeis University shows that a new method of modifying fat
in commercial products to replace unhealthy trans fats raises
blood glucose and depresses insulin in humans, common precursors
to diabetes. Furthermore, like trans fat, it still adversely
depressed the beneficial HDL-cholesterol.
Published online in Nutrition and Metabolism, the study demonstrates
that an interesterified fat--(a modified fat that includes hydrogenation
followed by rearrangements of fats molecules by the process
called interesterification) enriched with saturated stearic
acid--adversely affected human metabolism of lipoproteins and
glucose, compared to an unmodified, natural saturated fat. Interesterification
to generate a stearic acid-rich fat is fast becoming the method
of choice to modify fats in foods that require a longer shelf
life because this process hardens fat similar to oils containing
trans-fatty acids. The new study shows that interesterification,
which unnaturally rearranges the position of individual fatty
acids on the fat molecule, can alter metabolism in humans.
"One of the most interesting aspects of these findings
is the implication that our time-honored focus on fat saturation
may tell only part of the story," explained biologist
and nutritionist K.C. Hayes, who collaborated on the research
with Dr. Kalyana Sundram, nutrition director for palm oil
research at the Malaysian Palm Oil Board in Kuala Lampur.
"Now it appears that the actual structure of the individual
fat molecule is critical, that is, the specific location of
individual fatty acids, particularly saturated fatty acids,
on the glycerol molecule as consumed seems to make a difference
on downstream metabolism of fat and glucose," said Hayes.
Both Hayes and Sundram are experts on human lipid metabolism
and were instrumental in the development of Smart Balance®
Buttery Spreads, a blend of vegetable oils that improves the
cholesterol ratio.
Trans-fatty acids, which became ubiquitous in baked goods,
processed foods and restaurant cooking decades ago because
of their shelf life and other properties, are now being abandoned
by many producers of commercial products such as cookies,
crackers, pies, doughnuts, and French fries because they raise
LDL ("bad") cholesterol, lower HDL ("good")
cholesterol and contribute to heart disease.
The Malaysian-Brandeis collaboration compared trans-rich
and interesterified fats with an unmodified saturated fat,
palm olein, for their relative impact on blood lipids and
plasma glucose. Thirty human volunteers participated in the
study, which strictly controlled total fat and fatty acid
composition in the subjects' diet. Each subject consumed all
three diets in random rotation during four-week diet periods.
This study further confirmed previous studies in animals and
humans, indicating once again that trans fats negatively affect
LDL and HDL cholesterol. Surprisingly, the interesterified
fat had a similar, though weaker impact on cholesterol.
"In this study we discovered that trans fat also has
a weak negative influence on blood glucose. The newer replacement
for trans, so-called interesterified fat, appears even worse
in that regard, raising glucose 20 percent in a month,"
said Hayes.
"This is the first human study to examine simultaneously
the metabolic effects of the two most common replacement fats
for a natural saturated fat widely incorporated in foods.
As such, it is somewhat alarming that both modified fats failed
to pass the sniff test for metabolic performance relative
to palm olein itself," noted Sundram.
"Whether this reflects the amount of test fat consumed,
underlying genetics of the specific population examined, or
some unknown factor, requires further study because the apparent
adverse impact on insulin metabolism is a troubling finding,"
he added.
Note: This story has been adapted from a news release
issued by Brandeis University.
