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One-in-three girls and one-in-four boys had body fat levels considered
obese for adults, according to a study of more than 600 children and teens
living in the Houston area. That's a big jump from 20 years ago when
only one-in-six girls and boys exceeded the obesity threshold for adults32
percent fat for women and 25 percent fat for men. The study, still
ongoing, also found differences among white, black and Hispanic youths.
Hispanic youths had the highest average body fat32 percent for girls and
24 percent for boys. White girls had the lowest average body fat26
percentamong the females. And black boys averaged the lowest19
percentamong the males. All subjects were measured by two highly accurate
methods for assessing body composition: dual energy x-ray absorptiometry
(DEXA) and emissions of potassium-40, a radioactive form of the element
occurring naturally in the body in tiny amounts. This is the only study
worldwide to assess fat and lean composition of children in different
ethnic and racial groups. When complete, it should produce data on 1,000
childrenenough for developing charts that show normal ranges of body
composition similar to the height and weight growth charts in
pediatricians' offices.
Children's Nutrition Research
Center, Houston, TX
Kenneth J. Ellis, (713) 798-7132
Black children start their growth spurt two to five years earlier than
white or Hispanic children. This finding from a study of more than
600 children and teens points to the need to customize dietary
recommendations for different ethnic groups to provide the protein and
minerals for children when they need them. Black girls and boys tend to
grow taller and heavier and mature faster than white or Hispanic children.
At age 6, black girls begin adding significantly more muscle and bone than
white or Hispanic girls, while these two groups wait until around age
eight or nine for their growth spurt. Black boys begin to outpace white
and Hispanic boys at age seven and grow even faster at age 12, when white
and Hispanic boys are beginning their growth spurts. Current data on
changes in body compositionfat, muscle and boneduring childhood were
developed from data gathered in the 1950s, 60s and 70s on white children
only. And they only give an average value for different ages. This
ongoing study of boys and girls ages three to 18 aims to develop body
composition charts showing the range of normal growth patterns among the
major ethnic groups in this country. It shows that today's youths are
bigger and taller than those of three to four decades ago along with
having more body fat.
Children's Nutrition Research
Center, Houston, TX
Kenneth J. Ellis, (713) 798-7132
Black adolescent girls had lower aerobic capacity than their white
counterparts during a treadmill test, even though both ethnic groups had
the same amount of body fat. Researchers conducted the study of 93
girls, ages 11 to 16, because of scanty information on the physical
fitness of U.S. adolescents of different ethnic origins. Researchers
measured peak oxygen consumptionan indicator of fitness known as VO2maxin
40 black girls and 53 white girls while they ran on a treadmill to the
point of exhaustion. The black girls consumed 17 percent less oxygen than
the white girls during the test and reached exhaustion nearly a minute
earlier8.5 versus 9.4 minutes. Blood tests showed that hemoglobinthe
oxygen-carrying molecule in red blood cellswas six percent lower in the
black girls. Studies done in other countries suggest that ethnicity
contributes to differences in aerobic fitness. Researcher don't yet have
an explanation but suspect both genetics and lifestyle contribute to the
differences. They are currently analyzing data they collected on the
girls' body composition and resting metabolic rate for clues.
Children's Nutrition Research
Center, Houston, TX
William W. Wong, (713) 798-7168
James M. Pivarnik (formerly ARS), (517) 353-3520
Older people's need for dietary protein markedly differed in two
studiesindicating that more and larger studies are needed to resolve the
question of protein requirements after age 50. A two-week study of 12
men and women in their late fifties, sixties and seventies suggests that
the recommended dietary protein allowance (RDA) for people over age 50 may
need to be adjusted upwards to 1.0 to 1.25 grams per kilogram of body
weight each day (g/kg/d). The current RDA0.8 g/kg/dis the same as for
younger adults, because the data on older people has been too scanty to
establish a separate requirement. In this study, conducted at the ARS
center in Boston, researchers calculated the amount of protein volunteers
needed, using a formula adopted by the World Health Organization (WHO) in
1985. On average, the volunteers required a little more than the current
RDAabout 1.0 g/kg/djust to replace the protein they excreted daily. The
researchers also recalculated protein requirements for three earlier
studies using the newer WHO formula and got nearly the same estimatean
average of 0.9 g/kg/d. Their suggested 1.0 to 1.25 g/kg/d would cover
those who require more than average. By contrast, all 14 women in a
seven-week study stayed in balance while getting the RDA, suggesting that
0.8 g/kg/day is adequate. The women were between 51 and 70 years old.
Conducted at the ARS center in Grand Forks, ND, this study differed from
the Boston study in several ways. Most importantly, these diets provided
more calories per kilogram of body weight. When calorie intake is too low
to maintain body weight, people will burn protein to supply energy and
thus appear to need more than they actually do to renew tissues. Larger
studies need to be done to resolve the question of protein requirements
after age 50.
Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts, Boston, MA
Wayne W. Campbell (formerly ARS), (814) 865-3453
Grand Forks Human Nutrition Research Center, Grand Forks, ND
Janet Hunt, (701) 795-8328
Vitamin E, vitamin A and two other antioxidantslutein and
zeaxanthinhave been found in the eyes' lenses, suggesting they may help
protect against the formation of cataracts. Analyzing both healthy
and cataract-clouded human lenses removed during surgery, researchers
found significant levels of vitamins E and A, lutein and zeaxanthin.
These latter two compounds are carotenoidsplant pigments related to beta
caroteneand are abundant in yellow and dark green leafy vegetables, such
as spinach, broccoli and kale. No other carotenoids, including beta
carotene and lycopenetwo major carotenoids in human bloodwere found in the
lenses. Population studies have shown a relationship between carotenoid
or vitamin A levels in the blood and a lower incidence of cataracts. Of
the 31 lenses analyzed, those removed from Asian Indians, who
traditionally eat a lot of vegetables, had significantly higher levels of
the antioxidants than those from Americans. Among the American lenses,
antioxidant levels differed significantly, possibly reflecting a wide
difference in vegetable intake among Americans.
Jean Mayer Human Nutrition Research
Center on Aging at Tufts, Boston, MA
Kyung-Jin Yeum, (617) 556-3128
Obstetricians may someday monitor pregnant women's water weight gains
using harmless electrical current. A study by scientists with ARS and
the University of California at Berkeley may be the first to explore this
specialized use of a technique known as bioimpedance spectroscopy, or BIS.
During pregnancy, water accounts for most weight gain. But water buildup
outside cellsextracellular watercan lead to edema for the mother-to-be.
This sometimes painful swelling can raise blood pressure and cause other
complications. In tests of 10 pregnant women, aged 20 to 37, the
researchers found that BIS is faster and easier than options that require
drinking or injecting fluid containing a tracer. A BIS measurement also
is just as accurate, takes only two minutes and requires no blood samples,
unlike tracer methods. BIS sends a harmless sweep of electricity through
electrodes at the hand and foot. It distinguishes differences in
resistance, as the electricity travels easily through water or is impeded
by cell membranes. A computer converts these measurements into estimates
of total water in the body, and water outside and inside cells. Xitron
Technologies, Inc., San Diego, developers of the BIS instrument used in
the experiment, collaborated with ARS in the study.
Western Human Nutrition Research Center, San Francisco, CA
Marta D. Van Loan, (415) 556-5729
Children's Nutrition Research
Center, Houston, TX
William W. Wong, (713) 798-7168
A daily dose of the blue-green algae Spirulina may help prevent cancer
of the mouth, a study shows. The finding could benefit people in
developing countries where the algae is cheaper than vitamins. After one
year of consuming only one gram of the algae daily, 45 percent of the
volunteers had complete regression of the thick, white, pre-cancerous
patches in the mouth known as leukoplakia. Taking in to account those
volunteers who showed significant improvement raised the figure to 57
percent who benefitted from Spirulina. That compared to seven percent of
those who got a placebo. The studythe first human evaluation of the
cancer-preventive potential of Spirulinawas coordinated by an ARS
researcher and conducted in southwestern India where the incidence of
leukoplakia is high. The researchers tested Spirulina because it is an
inexpensive source of beta carotene and related carotenoids in many
developing countries. In other research, the algae has inhibited oral
cancer in animal studies, while beta carotene or vitamin A supplements
have reversed pre-cancerous conditions in people's mouths. Cancer of the
mouth and of the cervixwhich has the same kind of mucus membraneis on the
rise worldwide.
Beltsville Human
Nutrition Research Center, Beltsville, MD
Padmanabhan P. Nair, (301) 504-8145
Measuring blood levels of the amino acid homocysteine only after an
overnight fast could miss nearly half of the people with elevated
levels. Research has linked high homocysteine levels to increased
risk of heart disease and stroke. A second measurementtaken after a dose
of another amino acid, methionineis needed to identify all cases,
according to a study of 247 volunteers. That's because some people have a
low tolerance for methionine and convert it rapidly to homocysteine, which
raises blood levels. High blood levels of homocysteine may be damaging to
arteries. Researchers found that the test done after overnight fasting
failed to identify nearly half of the high-homocysteine cases. These
cases were detected only after volunteers got a dose of methionine. Both
tests are needed because three vitamins are involved in homocysteine
metabolism. The overnight fast test reveals those people with folate
(folic acid) or vitamin B12 deficiency, while the methionine test detects
people who lack vitamin B6. Also, the researchers streamlined the second
test so homocysteine can be measured two hours after a dose of methionine
instead of four or six hours.
Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts, Boston, MA
Andrew G. Bostom/Jacob Selhub, (617) 556-3356/-3191
People don't need to become severely deficient in magnesium for the
brain to become hyperactive. A new study confirms earlier reports
that a marginal magnesium intake overexcites the brain's neurons and
results in less coherencecreating cacophony rather than symphonyaccording
to electroencephalogram (EEG) measurements. Thirteen women consumed 115
milligrams of magnesium per day (mg/d)or about 40 percent of the
Recommended Dietary Allowancefor half of the six-month study. During the
other half, they got 315 mg/da little more than the 280 mg/d recommended
intake for women. After only six weeks on the marginal intake, EEG
readings showed significant differences in brain function. Magnesium is
the fourth most abundant element in the brain and is essential in
regulating central nervous system excitability. Clinical studies of
people severely deficient in this essential element have reported
epilepsy-type convulsions, dizziness and muscle tremors or twitching, as
well as many psychological symptoms, including irritability, anxiety,
confusion, depression, apathy, loss of appetite and insomnia. While the
marginal intake in this study did not produce such severe symptoms, it did
hype brain activity. This is the first experimental study in which
magnesium intakes were tightly controlled and EEG measurements were
analyzed by computer so that they could be statistically compared. Good
sources of magnesium include whole grains, nuts, peanut butter,
cottonseed, peanut and soybean flours, green leafy vegetables and
spices.
Grand Forks Human Nutrition Research Center, Grand Forks, ND
James G. Penland, (701) 795-8471
Last updated: October 29, 1996
Return to: Quarterly Report
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