Identical twins who ate both high-fat and low-fat diets in a controlled
study put a dent in the popular belief that dietary fat increases people's
calorie intake. On average, the seven sets of male twins chose about the same
number of calories when served a diet containing 20 percent fat calories and a
diet containing 40 percent fat calories. The two diets had the same
palatability, fiber content and calories per ouncefactors that may affect
calorie intake. It now appears that the number of calories per ounce of food
may be more important than fat content, supporting some earlier, short-term
These findings may help explain why the U.S. population has added weight,
although fat intake has dropped and low-fat and fat-free products have flooded
the market. Many such products are calorically dense. The findings also suggest
that genes exert some control over a person's preference for a high- or low-fat
diet. Four sets of twins ate more calories from the high-fat menu. The other
three pairs preferred the low-fat diet, indicating that genes may influence the
tendency to overeat certain diets. The men metabolized both diets with equal
The study, published in the American Journal of Clinical Nutrition
(vol. 66, pp. 1332-1339), was funded jointly by ARS and the National Institutes
of Health. A larger study involving 90 sets of identical twins is now in
progress to determine to what extent people's genes contribute to body fat and
For more information, contact Edward Saltzman, (617) 556-3245,
or Susan Roberts, (617) 556-
3237, Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts, Boston, MA.
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Sweet-smelling methyl jasmonate, a natural compound in all plants, protects
produce from pathogens and doubles shelf life. Strawberries exposed to methyl
jasmonate vapor for 24 hours at 68 degrees F resisted gray mold for 14 days
with no change in fruit firmness. Gray mold, Botrytis cinerea, is a
major fungal disease of harvested fruits and vegetables. Treatment of fresh-cut
celery and green peppers eliminated browning and decreased bacterial growth a
thousandfold for up to 2 weeks at 50 degrees F. The treatment also controlled
soft rot on the peppers. Another plus: Methyl jasmonate slowed grey mold on
It is thought that the chemical elicits proteins in living plants and
harvested produce that make them more resistant to temperature changes and
attack by insects, bacteria and fungi. Most plants contain small amounts of
jasmonates, but jasmine and honeysuckle contain high levels. Methyl jasmonate
is available commercially and is inexpensive. Truckloads of produce can be
treated with less than one ounce, which costs about $30. It acts within a
couple of hours and leaves no residue.
In related research, the scientists mixed citric acid and
N-acetylcysteinea common, sulphur- containing amino acidto keep
banana slices for 14 days at 40 degrees F without browning. The treatment not
only allows bananas to be marketed as fresh-cut, but also retards browning and
reduces decay in fresh-cut slices of apple, pear, peach, plum, nectarine and
avocado. Treated apples did particularly well, holding up for 50 days in cold
storage without any change in flavor.
An article detailing the treatments is on the World Wide Web at:
For more information, contact J.
George Buta, Harold E.
Moline, and Chien Yi Wang,
(301) 504-6128, Horticultural Crops
Quality Laboratory, Beltsville, MD.
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Vegetarians who include milk and eggs in their diets can meet their zinc
requirements by eating plenty of whole grains and legumes such as beans and
peas, researchers have found. The researchers studied 21 women who consumed
both a lacto-ovo vegetarian dietone containing milk and eggs but no other
animal productsand a typical U.S. diet for 8 weeks each.
Among its many functions, zinc helps the body guard against infections and
repair wounds. In the U.S., however, meat is the major source of zinc. It's
important to know if the nearly 2 million U.S. lacto-ovo vegetarians may be
depriving themselves of adequate zinc. It's particularly important since
typical vegetarian diets contain 10 to 30 percent less zinc than non-vegetarian
diets. They also contain a lot of fiber and phytate, which tend to reduce
absorption of minerals such as zinc.
In the study, the vegetarian diet supplied 14 percent less zinc despite
efforts to include high-zinc foods. And the women absorbed 21 percent less zinc
from the vegetarian diet, putting their absorption deficit at 35 percent.
However, they absorbed enough to replace what they excreted, and their health
remained good. In fact, the two diets produced very little difference in
balance measurementsabsorption minus excretionfor zinc and several
The women's iron status was also assessed, because the body absorbs iron
much more readily from animal foods than from plant foods. The women absorbed
70 percent less iron while eating the vegetarian diet, but they showed no signs
of iron-poor blood after 8 weeks. Read more details on the World Wide Web at:
For more information, contact Janet R. Hunt, (701) 795-8328,
Grand Forks Human Nutrition Research
Center, Grand Forks, ND.
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Imagine eating triple-boiled green beans, carrots, chicken, turkey or ham at
lunch or dinner for weeks in a row. Now be thankful you don't have to: 10
dedicated women, aged 49 to 63, already took the challengefor the cause
of science. They volunteered in a 12-week study that yielded new information
about women's need for folate, an essential B vitamin. The findings add to
other evidence that the Recommended Dietary Allowance of folate for
women180 micrograms (mcg) dailymay need to be increased.
Researchers monitored several folate-linked indicators of good health. These
include DNA formation, white blood cell makeup, and regulation of the amino
acid, homocysteine. Blood levels of homocysteine can accumulate to unhealthful
levels in people who do not eat enough folate. All three indicators were
compromised in the women after nine weeks of eating meals that provided only 30
to 60 percent of the RDA for folate. (Triple-boiling key foods knocked out
about half of their folate.)
Even this mild folate deficiency hampered DNA formation. What's more, seven
of the women exhibited more DNA damage, based on an increase in the number of
micronuclei in their white blood cells. Excess DNA damage may increase risk of
cancer and birth defects. Half of the women continued to have high blood levels
of homocysteine two weeks after the low-folate diet ended, even though they
were getting 1.6 times the folate RDA for those two weeks.
Orange juice, liver, eggs, dark-green leafy vegetables, peas and beans, and
nuts and seeds are good sources of folate. The vitamin is especially important
to women of child-bearing age. It helps prevent birth defects such as spina
bifida. Makers of enriched bread, flour, cornmeal, rice, pasta and other grain
products are required to fortify these foods with folate. Read more about the
subject on the World Wide Web at:
For more information, contact Robert A. Jacob, (415) 556-3531,
Western Human Nutrition
Research Center, Presidio of San Francisco, CA.
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Special nutritional guidelines for teenage mothers who are nursing may be a
good idea, according to preliminary research results. In a comparison of breast
milk between 11 teen and 11 adult moms, the breast milk had similar nutrients.
But teens produced 37 to 54 percent less milk. Over the long term, that would
shortchange the teens on meeting their babies' nutritional needs. The results,
published in the Journal of Adolescent Health (vol. 20, pp. 442-449),
were statistically significant even after adjusting for differences in feeding
time and nursing frequency.
The average age of the teen moms was 16. Researchers suspect that their
lower milk production may be due to the fact that they have not yet completed
their own growth. Since a teen mother has this additional nutrient demand, her
body may "choose" to favor her and reduce milk production for her
To test this thesis, the research team measured body composition, diet and
milk production of 24 teenage mothers, half of whom breast-fed their babies.
Eleven other teens who had never been pregnant were studied for comparison.
Preliminary findings suggest that nursing teens continue to add muscle mass to
their bodies, indicating continuing growth.
Teens who breast-fed appeared to consume 23 percent more calories and
vitamin B6, and 40 percent more protein. Their dietary needs returned to
regular levels after they stopped breast- feeding. A more detailed article on
the subject is on the World Wide Web at:
For more information, contact Kathleen Motil, (713) 798-7180,
Children's Nutrition Research
Center, Houston TX.
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A single-cell parasite, Cryptosporidium parvum, has for the first
time been found in oysters. An ARS researcher and colleagues with Johns Hopkins
University and the National Oceanic and Atmospheric Administration found C.
parvum oocystsencased eggsin oysters taken from the mouths of
six rivers feeding the Chesapeake Bay. Some of the oysters had 4,000
oocystsmany times the infective dose.
The researchers also demonstrated that oocysts could develop in mice. This
indicates that they pose a potential risk to humans who eat raw oysters,
although there have been no human outbreaks attributed to oysters. A report on
the study is in Applied and Environmental Microbiology (vol. 64, pp.
C. parvum are protozoan parasites found in waterways worldwide. When
ingested, they can infect gastrointestinal cells, where they evoke cramping,
diarrhea and sometimes nausea and vomiting four to 10 days later. Because of
the long incubation period, C. parvum is often not connected with the
flu-like symptoms. Symptoms range from mild to severe in healthy people and can
lead to chronic diarrhea, dehydration and death in people who have a weak
The oocysts don't survive temperatures above 164 degrees Fahrenheit, so
boiling or frying shellfish would prevent infection. But they do survive
chlorine quite well. In 1993, more than 400,000 Milwaukee residents suffered
C. parvum infections from contaminated drinking water. Smaller outbreaks
have occurred around the country.
The parasite can infect all mammals. Feces from humans or domestic and wild
mammals, including white tail deer, can potentially contaminate waterways.
Geese can transport oocysts through their feces, the researchers found, and
contribute to their spread into waterways.
For more information, contact Ronald Fayer, (301) 504-8750,
Disease Resistance Laboratory, Beltsville, MD.
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A new ARS-developed product that reduces potential salmonella contamination
in poultry is being marketed by MS Bioscience of Dundee, IL. The
product, called PREEMPT, prevents salmonella bacteria from taking hold in the
intestines of newly hatched chicks. ARS researchers isolated 29 beneficial
intestinal bacteria from older birds and blended them into a mixture that can
be sprayed onto newly hatched chicks to give them the same level of natural
protection against salmonella as older chickens have.
The U.S. Food and Drug Administration has approved this bacterial mixture
based on field tests with 80,000 chickens in U.S. commercial chicken houses. It
marks the first time FDA has approved a mixture of bacteria as a type of animal
drug known as a "competitive exclusion product." ARS has patented the
bacterial mixture, known originally as CF-3, and the method for producing it.
While PREEMPT can help poultry producers reduce the risk of salmonella
transmission to people, it should be used as part of a comprehensive program of
proper food handling and preparation measures designed to minimize the risk
posed by all potential food borne pathogens. Chicken must still be properly
handled and thoroughly cooked to be safe.
There are an estimated 2 million cases of salmonella poisoning each year. Of
these, about 40,000 cases are culture-confirmed. Most exposure is from raw or
undercooked meat, poultry, milk and eggs. The human health care bill for
salmonellosis averages about $4 billion annually.
For more information, contact Larry H.
Stanker, (409) 260-9484, Food and Feed
Safety Research Unit , College Station, TX.
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A new way to detect unseen fecal contamination on fresh meat could help
industry meet new food safety regulations designed to control disease-causing
bacteria. Feces are the major source of bacterial contamination in livestock
and poultry slaughterhouses. ARS and Iowa State University researchers built a
detector, using fluorescent spectroscopy, that illuminates unseen fecal
contamination on meat. The device is adaptable to any size packing plant. When
redesigned as a hand-held unit, similar to metal detectors used in airports,
the instrument could alert meat packers to fecal contamination within seconds.
The contaminated carcass could then be sanitized before the contamination
Meat packers now visually inspect carcasses for fecal contamination. With
the new technology, this job will be easier, faster and more accurate. The
technology is timely because USDA's Food Safety & Inspection Service (FSIS)
is enforcing a zero tolerance standard for fecal contamination on livestock and
poultry carcasses. The researchers are patenting their technology, and
discussions are under way with industry cooperators on possible commercial
For more information, contact Mark A. Rasmussen, (515) 239-8350
or Thomas A. Casey, (515)
239-8376, National Animal Disease
Center, Ames, IA.
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A new vaccine promises to suppress future outbreaks of the Hong Kong
"bird flu"--H5N1. The flu jumped directly from chickens to humans,
killing several Hong Kong residents by late 1997. Researchers with ARS and
Protein Sciences Corporation of Meriden, Conn., originally developed a vaccine
to protect against an avian influenza strain that appeared in Mexico in 1995.
The Mexican strain is in the same genetic family as the Hong Kong virus, but
gave no evidence of infecting people. Its relatedness, however, prompted the
researchers to develop another similar vaccine against the Hong Kong strain
late last year. The tests proved 100 percent effective in protecting birds.
Scientists in Hong Kong are now retesting the vaccine's efficacy on that
side of the globe. In the United States, the H5 vaccines are being evaluated
for approval in case of future outbreaks on this continent. An effective
vaccine could reduce the likelihood of the virus' spread in poultry if it
returns. The virus is 100 percent lethal in chickens.
To develop the vaccines, Protein Sciences Corporation combined its own
patented technology with ARS insights on the virus' genetic makeup and
ARS-supplied genetic material. The technology uses an insect virus,
baculovirus, to produce huge quantities of a single viral protein.
For more information, contact Mike Perdue, (706) 546-3433,
Poultry Research Laboratory, Athens, GA, or
Bethanie Wilkinson, (203)
686-0800, Protein Sciences Corporation , Meriden, CT.
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Mouth-watering, eye-pleasing fruit could be one payoff of research to
increase the natural compounds in plant foods that appear to enhance health.
Many of these compounds, called phytonutrients, are produced during the
ripening process. The dilemma: how to allow fruit to ripen naturally on the
tree or vine to get the maximum in phytonutrients while retarding the softening
that occurs after the fruit is picked.
That's one research area suggested for exploration at ARS-sponsored
workshops on food, phytonutrients and health in March. About 115 nutrition,
health, plant and post-harvest scientists from ARS, universities and private
industry met for three days to define research priorities and discuss the
federal role. It will take such interdisciplinary research teams to ensure that
the U.S. food supply provides optimum nutrition.
News about potential benefits of broccoli, garlic, tea, soybeans and
tomatoes has raised public awareness and increased research on phytonutrients.
The U.S. may be on the threshold of the next agricultural revolutionnot
more products, richer ones. But scientists worry that the publicity for
phytonutrients is far ahead of the science.
Among the most pressing needs mentioned: Nutrition and health scientists
need to decide which phytonutrients are most promising before plant scientists
invest time and money in enriching crops or in identifying the cultivation,
harvesting, handling and storage practices that conserve phytonutrients.
Nutrition and health scientists are blocked in identifying the important
phytonutrients by a lack of sensitive assays to indicate small changes in risk
for cardiovascular disease, cancer or other maladies. And all said they need
accurate analytical methods for detecting phytonutrients.
Participants encouraged ARS to develop an Internet site to keep track of
phytonutrients as they emergethere are a dozen classes and thousands of
individual compounds that may qualifyand to exchange information.
Everyone agreed that new phytonutrient-enriched varieties must be as
high-yielding, insect resistant and as tasty as today's foods.
For more information, contact Roger
Lawson, (301) 504-5912, ARS National Program Staff, Beltsville, MD .
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