Reduced-calorie diets that provide nutritious, well-balanced meals
might nevertheless weaken the body's immune system. That's the suggestion
of ARS researchers who conducted a preliminary study of 10 women volunteers.
The scientists wanted to pinpoint how dieting affects the immune system,
since one-third of all Americans are overweight, and many choose to cut
calories to shed pounds. Most of what is known about the interaction between
dieting and the immune system is based not on moderate dieting but on extreme
cases such as anorexia nervosa or acute starvation. In the experiment, scientists
cut the volunteers' calories by about half--a moderate amount. That meant
volunteers ate about 1,300 calories a day for 12 weeks. Women in the study
were 28 to 46 years old and 45 to 75 pounds overweight. Scientists monitored
two dozen standard indicators of the women's immune systems before, during
and after the reduced-calorie stint. All the women remained healthy during
the study. But scientists noted a 30 to 35 percent drop in the number of
natural killer cells--part of the body's defense against tumors and viral
infection--in the blood. And three serum immune system proteins (IgG, IgA
and C3) decreased 10 to 15 percent. More needs to be learned about these
changes. But researchers say the findings underscore the importance of medical
supervision for any weight loss program.
Western Human Nutrition Research Center, San Francisco, CA
Darshan S. Kelley, (415) 556-4381
More evidence of a B vitamin's importance for a healthy heart emerged
from an ARS study. Researchers found that skimping on the vitamin, folate,
may raise blood levels of an amino acid, homocysteine, in about a month.
High homocysteine levels have been linked to low folate and blamed for increased
risk of heart attack or stroke. Ten men, age 33 to 46, volunteered for the
108-day study by researchers with ARS and the University of California at
Los Angeles. At various times, volunteers received 12, 84 or 220 percent
of the Recommended Dietary Allowance (RDA) of folate. The current RDA for
men is 200 micrograms. The low-folate stints made the test unique. Four
volunteers in the study showed moderately elevated homocysteine after only
30 to 45 days of the lowest-folate intake. Their homocysteine levels quickly
dropped to normal with the 220 percent RDA intake. Raising the RDA would
increase the margin of safety, the researchers suggest. Folate is essential
for growth and health of cells and proper functioning of the brain and hormones.
The many good dietary sources include liver, leafy green vegetables, lentils
and other dry legumes, orange juice and fortified breakfast cereals.
Western Human Nutrition Research Center, San Francisco, CA
Robert A. Jacob, (415) 556-3531
Today's method for checking the body's supply of vitamin A might be replaced
within a few years by a simple, fast and easy blood test that ARS researchers
are now developing. When ready, the blood test would make the current
technique--a liver biospy--unnecessary. Researchers have newly paired two
laboratory techniques--supercritical fluid extraction and reversed phase
liquid chromatography--to more accurately measure vitamin A supplies in
liver samples. Their analyses should quicken their search for a compound
in blood that would give an equally accurate reading. Liver biopsies, though
painful, are currently used for vitamin A tests because that is where the
body keeps its largest reserves of this vitamin. The blood test that the
researchers envision could be used by physicians and other healthcare professionals
to check their patients' vitamin A stores. And it might be used in the national
health and nutrition surveys, co-sponsored by USDA, that are a key source
of new information for evaluating and fine-tuning the nation's Recommended
Dietary Allowances--or RDAs--for essential nutrients such as vitamin A.
According to current USDA estimates, about 55 percent of all Americans receive
less than the RDA for vitamin A.
Western Human Nutrition Research Center, San Francisco, CA
Betty J. Burri (415) 556-6285
Find out more by visiting Human Nutrition Research
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