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A new thesis suggests that too little dietary copper—common in
industrialized countries—may contribute to aging. The thesis is
based on animal studies bolstered by indirect evidence. ARS researchers
are finding evidence that copper deficiency spurs sugar molecules to
attach to protein molecules. The process, known as protein glycation,
is thought to cause much of the tissue damage in people with diabetes.
And this glycation increases in all of us as we age.
When blood sugar is high, as often occurs in copper-deficient rats,
it's more likely that sugar molecules will attach to proteins—called
early glycation. If sugar levels stay high, the sugars' free ends can
attach to other proteins or other sites on the same protein—called
advanced glycation. These cross links bend proteins out of shape, rendering
them useless.
Researchers found that both the early and advanced stages of protein
glycation increased significantly in rats fed a copper-deficient diet.
One sensitive indicator of advanced glycation was at least sixfold higher
in the copper-deficient rats. It was nearly undetectable in the control
rats, they reported in the Journal of Nutritional Biochemistry,
1999 (vol. 10, pp. 210-214).
Human diets contain relatively more copper than the rat diets. But
the average copper content of U.S. diets falls below the suggested range
of 1.5 to 3.0 milligrams daily. The researchers speculate that years
of eating a diet low in the mineral may contribute to the age-related
decline in tissue function by increasing glycation. So far, they have
looked only at glycation of blood hemoglobin and serum proteins. But
it can also happen to structural proteins that form the tissues. High-copper
foods include whole grains, oysters, liver, nuts (particularly Brazil
nuts), seeds, cocoa and chocolate.
For more information, contact Jack T. Saari, (701) 795-8353, Grand
Forks Human Nutrition Research Center, Grand Forks, ND
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Peak athletic performance depends on adequate zinc, according to a
study of the effects of a low-zinc diet on 12 athletic men in their
twenties. While most athletes don't have to worry, those who avoid beef
and load up on carbohydrates may fall short in zinc. Beef is the major
source of this essential trace element in the U.S. diet. Wrestlers,
gymnasts and ballerinas who eat sparingly to maintain a low body weight
may also be at risk of too little zinc. The recommended 12-15 milligrams
per day is adequate for peak performance. Supplementing with several
times that level can cause health risks.
The study focused on a zinc-containing enzyme—carbonic anhydrase—in
red blood cells. The enzyme helps red blood cells pick up carbon dioxide
and drop it off in the lungs to be exhaled. This exchange helps maintain
the chemical environment muscle cells need to contract and produce energy.
If the exchange is sluggish, the athlete pays the price in performance.
For nine weeks each, the men ate a diet containing 18 mg of zinc daily
and another containing only 3 mg. After the low-zinc diet, the activity
of the carbonic anhydrase enzyme was lower. The men had significant
drops in peak oxygen uptake and peak carbon dioxide output as they cycled
all-out on an ergometer. Their respiratory exchange ratios also dropped,
indicating energy production during peak exercise was not up to snuff.
The low-zinc diet also depressed these measurements while the men cycled
at 75 percent of peak capacity.
For more information, contact Henry
C. Lukaski, (701) 795-8355, Grand
Forks Human Nutrition Research Center, Grand Forks, ND
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Getting blueberry extract daily for eight weeks reversed some loss
of balance and coordination in aging rats. And it improved the animals'
short-term memory, as did strawberry and spinach extracts, researchers
reported in the Journal of Neuroscience, 1999 (vol. 19, pp. 8114-8121).
The 19-month-old rats were the equivalent of 65- to 70-year-old humans.
They ate the human equivalent of at least a half cup of blueberries
daily.
The most significant findings are the improvements in coordination
and balance, the researchers say, because little else has reversed deficits
in motor function. They attribute the reversals largely to improvements
in nerve cell signaling in the neostriatum—an area of the brain
that controls both motor and cognitive function. The same researchers
earlier reported that high-antioxidant fruits and vegetables prevented
some loss of function in aging rats (see April 1999 Food & Nutrition
Research Briefs).
The findings hold hope for older people. Memory and motor function
are among the first to go in humans as well as rats. Blueberries score
highest in the ORAC assay, with strawberries and spinach in the top
seven. Other high scorers include prunes, raisins, kale, blackberries
and raspberries. ORAC measures the ability of foods, blood plasma and
just about any chemical mix to subdue oxygen free radicals in the test
tube. These oxygen radicals can damage cell membranes, DNA and other
delicate machinery and are blamed for many of the dysfunctions and diseases
of aging.
In the study rats, motor function starts to decline at about 12 months
and is obvious by 15 months. By 19 months, the length of time these
rats are able to traverse a narrow rod before losing balance normally
drops from 13 seconds for a young rat to 5 seconds. After getting the
blueberry extract, the rats stayed on the rod for an average 11 seconds.
Daily doses of strawberry and spinach extracts improved short-term
memory about as well as the blueberry extract, but none improved long-term
memory. For humans, an example of short-term memory is the ability to
remember a phone number long enough to dial it.
For more information, contact James A. Joseph, (617) 556-3178, or
Barbara Shukitt-Hale, (617)
556-3118, Jean Mayer USDA Human
Nutrition Research Center on Aging at Tufts University, Boston,
MA
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Some day, health professionals will have a fairly complete profile
of the human genes that influence heart disease risk. Individuals could
then adopt the habits most likely to reduce risk because different genes
or combinations of genes respond differently to changes in diet, exercise,
smoking, alcohol consumption or medications such as cholesterol-lowering
drugs.
One pioneer in this field—located at the ARS center in Boston—focuses
on genes that control blood lipids. His team has identified several
of the 40 or so genes so far known to affect cardiovascular health.
He estimates that hundreds of genes may ultimately go into a risk-analysis
database.
Four main disorders under genetic control contribute to heart-disease
risk: high blood lipids, high blood pressure, obesity in the abdomen,
and impaired glucose tolerance, resulting in type II diabetes. Whether
a disorder manifests itself depends upon an individual's lifestyle and
age. Moreover, one gene can affect another. For example, in an obese
individual, an obesity gene can trigger a normally beneficial gene for
blood lipids to express high LDL ("bad") cholesterol and triglycerides.
But if the individual stays lean, the beneficial gene could prevail—all
other things being equal.
Such genetic interactions have produced conflicting results in diet
intervention studies and led to public confusion over the value of changing
one's fat intake. One group that can benfit are people with a genotype
known as APOE4, according to the researcher. If they follow the standard
cholesterol-lowering diet, they can expect about a 30-percent decrease
in LDL cholesterol. That's about the level of decrease expected from
cholesterol-lowering drugs—except for people with this genotype.
They respond poorly to the best of these drugs.
For more information, contact Jose M. Ordovas, (617) 556-3102, Jean
Mayer USDA Human Nutrition Research Center on Aging at Tufts University,
Boston, MA
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The level of lactase—the enzyme responsible for the digestion
of milk sugar—might help physicians identify premature infants
at risk for feeding intolerance, a common complication and main cause
of extended hospitalizations. In a recent study of 135 premature infants,
lactase activity was a strong indicator of intestinal maturity, which
affects an infant's ability to handle feedings.
Premature infants can't be released from the hospital until they are
on full human milk or formula feedings. As a rule, they are started
on intravenous feedings at birth. Generally after two weeks, they receive
supplemental feedings of human milk or special preemie formula, which
are gradually increased.
In the study, however, half of the infants began receiving supplemental
feedings at four days of age, the remainder at the traditional 15-day
mark. At 10 days of age, the early feeding group's lactase activity
was double that of the infants receiving only intravenous feedings.
At 28 days, it was still 60 percent higher even though both groups were
getting similar amounts in their supplemental feedings, the researchers
reported in the Journal of Pediatrics, 1998 (vol. 133, pp. 645-649).
Infants with the highest lactase activity were most likely to achieve
full feedings sooner and least likely to have abdominal complications.
Those who received early feedings of human milk had the highest lactase
activity.
For more information, contact Robert Schulman, (713) 798-7145, Children's
Nutrition Research Center at Baylor College of Medicine, Houston,
TX
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Premature infants fed breast milk fortified with extra nutrients fare
better than those receiving special preterm formulas. That's what researchers
found in a study of 108 infants born between 11 and 13 weeks prematurely
and weighing less than 2.5 pounds each.
The preemies were fed either a special preterm formula or fortified
breast milk, depending on parental wishes. Within each group, milk feedings
were initiated at different times, and the tube-feeding method was varied
to determine an optimal feeding regimen. Of all the strategies tested,
fortified human milk influenced premature infant health the most, the
researchers reported in Pediatrics, 1999 (vol. 103, pp. 1150-1157).
The infants receiving fortified human milk "graduated" from
intravenous to milk feedings faster and had fewer of the complications
common in premature infants. For instance, they had fewer infections
in the blood and fewer cases of an intestinal inflammation that often
requires surgery. They also needed less medication to control spitting
up and were discharged from the hospital an average of two weeks sooner
than their formula-fed counterparts.
Breast milk contains antibodies and other substances that encourage
the growth of good bacteria in an infant's intestinal tract and also
inhibit the harmful ones that can invade an infant's system and cause
problems. But human milk fed to premature infants must first be fortified
with additional protein and minerals like calcium and phosphorus. Before
these extra nutrients were added to formulas or incorporated into fortifiers
for human milk, premature infants grew poorly and developed bones that
fractured easily.
For more information, contact Richard J. Schanler, (713) 798-7176, Children's
Nutrition Research Center at Baylor College of Medicine, Houston,
TX
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A new ARS-patented antibody quickly pinpoints a major antibiotic given
to dairy cows and meat animals. ARS researchers developed a new test,
using this antibody, to detect the antibiotic Ceftiofur. Ceftiofur is
used to treat mastitis in dairy cows and respiratory diseases in cattle,
pigs, and poultry.
The federal Food and Drug Administration routinely screens milk, and
USDA's Food Safety Inspection Service routinely checks meat products,
to make sure they don't exceed the tolerances for residues from antibiotics
approved to treat animals. Currently, these agencies measure residues
by using time-consuming laboratory analytical methods.
The test, with the ARS-patented antibody called CEFT-116, is much quicker
and easier than chemical analyses. It can detect Ceftiofur in the low-part-per
million (ppm) range in hundreds of milk samples per day. The immunoassay
is reported in Food and Agricultural Immunology, 1998 (vol. 10,
pp. 121- 132). The antibody is licensed to a company for incorporation
into an immunoassay for measuring Ceftiofur in milk.
The researchers envision that CEFT-116 can be used alone or incorporated
in a test kit along with other antibodies. The advantage of developing
an immunoassay kit is that it can be used in the field by the dairy
and meat industries as a way to prescreen their products for safety.
For more information, contact Larry H. Stanker, (409) 260-9484, Food
and Feed Safety Research Unit, College Station, TX
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An artificial gut invented by ARS scientists promises to accelerate
knowledge about the amount of iron available from food and food supplements.
The system is the first to model in the lab what occurs in the human
intestinal tract. The research has already led to suggestions for improving
the nutritional makeup of infant formula.
Iron deficiency is the world's most prevalent nutrient deficiency.
Even in developed countries, it remains a serious concern for women
during pregnancy and childbearing years. Children, too, must receive
proper iron nutrition. So researchers developed an in vitro model that
couples simulated food digestion with a human intestinal cell line,
Caco-2. The model, reported in the Journal of Nutrition, 1998
(vol. 128, pp. 1555-1561), allows food digestion to occur simultaneously
with opportunity for nutrient uptake by Caco-2 cells.
It is a fast, inexpensive, easy method for determining the relative
availability of iron from different foods or from different crop varieties
of the same food. So far, researchers have used the system to investigate
the iron availability of rice cereal, infant formulas and iron supplements.
It should have broad applications for studying staples like rice, corn,
wheat and beans; food supplements; pharmaceutical iron preparations,
and baby foods such as formula, cereals and purees. With continued improvement,
the model may eventually be used to measure the bioavailability of other
micronutrients, such as vitamin A, zinc, selenium and iodine.
For more information, contact Raymond P. Glahn, (607) 255-2457, U.S. Plant,
Soil and Nutrition Laboratory, Ithaca, NY
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Rats raised on a chromium-deficient diet showed the earliest stage
of diabetes—high blood insulin levels—in a study recently
reported in Metabolism, 1999 (vol. 48, pp. 1063-1068). The finding
underscores that chromium is necessary for maintaining normal glucose
tolerance, the researchers concluded. And it suggests that low-chromium
intakes—very common in industrialized nations—may contribute
to the onset of Type 2 diabetes mellitus, or middle-age diabetes, over
the long term.
The hormone insulin escorts blood glucose into body cells and enables
the cells to use that glucose for fuel. Diabetes begins when the cells
become less sensitive to insulin. As the cells become insensitive to
insulin, the body produces more of it. So high blood insulin is an early
indicator of potential diabetes. By the time blood glucose is elevated,
a person already has the disease. Chromium is one of the keys to maintaining
the cells' sensitivity to insulin. Good sources of the mineral include
fortified cereals and whole grain products.
During a glucose tolerance test, rats that got virtually no chromium
in their food or water for three months had insulin levels twice as
high as a group that got chromium-fortified water or a control group
fed a standard chow that contains chromium. In animal studies, the effects
of chromium deficiency are seldom obvious until the animals are stressed.
The glucose tolerance test with its sugar load was the stressor in this
study.
For more information, contact Richard
A. Anderson, (301) 504-8091, Beltsville
Human Nutrition Research Center, Beltsville, MD
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For the first time, food and nutrient intakes of Mexican Americans
and other people of Hispanic origin are available from USDA. The data
are drawn from the 1994-96 What We Eat in America Survey, also known
as CSFII, managed by ARS.
The data show that Mexican Americans eat more fiber than other Hispanics,
non-Hispanic whites and non-Hispanic blacks. The average fiber intake
for all Mexican Americans was 17 grams daily, closer than the other
groups to the 20-30 grams recommended by the National Institutes of
Health. Adult Mexican-American males age 20 and over consumed nearly
24 grams of fiber on average, while teenage males consumed nearly 20
grams.
Legumes may contribute a large portion of that fiber in the Mexican-American
male diet. Adult males averaged 107 grams of legumes a day. That's double
the intake of other Hispanics and almost four times greater than the
non-Hispanic groups. Teenage Mexican-American males consumed two to
six times more legumes than the other groups, averaging 71 grams daily.
Not surprisingly, Mexican Americans eat more tortillas and taco shells
than other Hispanics—about twice as much. The latter group eats
three times more rice than Mexican Americans. Mexican Americans also
lean toward whole milk, which accounts for 63 percent of milk consumed,
compared to 59 percent for other Hispanics, 70 percent for blacks and
25 percent for whites.
Both Hispanic groups were low in the same nutrients as the general
population, with intakes of vitamin E, calcium and zinc below recommendations.
To view the data tables, visit the web site of USDA's
Food Surveys Research Group. The raw data are available on CD-ROM
from the National Technical Information Service at 1-800-553-6847 (Accession
No. PB98-500457).
For more information, contact Katherine Tippett, (301) 504-0344,
Beltsville Human
Nutrition Research Center, Beltsville, MD
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