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Consuming small amounts of milk or yogurt can significantly
increase zinc absorption among impoverished people
living on plant-based diets, but has little effect
on iron absorption, according to a CNRC study recently
published in the Journal of Nutrition.
"Milk is the most common animal food provided
in nutritional support of impoverished populations,
yet there has been controversy over the specific effects
of milk on zinc absorption and whether the calcium
present in milk significantly impairs the absorption
of iron from plant-based diets," said Dr. Ian
Griffin, an assistant professor of pediatrics at Baylor
College of Medicine who studies zinc metabolism at
the CNRC.
Zinc and iron deficiencies, which causes poor growth,
impaired immune function, and delayed mental development,
are major health problem in developing countries.
"People living in low-income areas of developing
countries have little access to zinc-rich foods like
meat," he said. "In addition, the cereals and
legumes that make up the bulk of their diets contain
large amounts of fiber and compounds called phytates,
which severely limit the body's ability to absorb
the little zinc that is present."
For the study, forty eight women living in rural
Mexico who normally consumed a plant-based diet ate
two test meals a day consisting of tortillas and black
beans plus either water, one cup milk, or one-half
cup flavored yogurt, for two weeks. Iron and zinc absorption
was measured using stable-istotope "tracers."
Griffin found that compared to the women in the
water group, zinc absorption was 50 percent higher
in the milk group and 68 percent higher in the yogurt
group. Iron absorption rates did not differ among the
women.
According to Griffin, although calcium is known
to reduce iron absorption from a single meal,
finding no effect on iron absorption
in this study was not entirely unexpected. "Other
studies have suggested that over time people adjust
their iron absorption to account for the increased
calcium intake, and their iron absorption returns to
normal," he said.
The reason why dairy products, which are not zinc-rich
foods, increased zinc absorption remains unknown. However,
Griffin believes that the proteins in milk may help
keep the little zinc that's there in a form that is
easily absorbed by the body.
"Although the amount of zinc in milk might
appear to be a 'drop in the bucket,' the overall affect
is large because so little zinc is absorbed from a
plant-based diet," he said.
ut is this significant an individual's zinc health? "When
nutritional status is so poor, every 'drop' counts," he
said. |
