Are you overweightwith a body mass
index (BMI) between 25 and 30and your blood lipids are higher than your
doctor would like? Then you'll probably benefit more from cutting those extra
pounds by eating fewer calories and increasing physical activity than you would
from cutting dietary fat. That's the gist of a study done in Spain by
researchers at the University of Cordoba Medical School and at the ARS-funded
center in Boston.
Two different heart-healthy diets were less
effective at improving the cholesterol profile of overweight men than of
normal-weight men. The findings extend earlier evidence that dietary changes
don't have much of an effect on the blood lipids of obese peoplethose who
have a BMI over 30.
Total cholesterol in the overweight men
dropped less than half that of the lean men7 versus 16 percentafter
switching from a diet high in total fat and saturated fat to one recommended by
the National Cholesterol Education Program (NCEP). Likewise, artery-damaging
LDL cholesterol dropped 9 percent in the overweight group versus 21 percent in
the lean group. The NCEP diet is low in fat28 percent of total
calorieswith only 10 percent saturated fat.
A second heart-healthy diet also had less
impact on total and LDL cholesterol in the overweight men. Although this diet
was high in fat38 percent of total caloriesmore than half of it (22
percent) was monounsaturated fat, the predominant fat in olive or canola oils.
However, this diet produced a much bigger drop in triglycerides in the
overweight group, compared to the lean group: 26 percent versus 4 percent. High
triglycerides are associated with reduced glucose tolerancethe earliest
stage of diabetes. And evidence is mounting that high trigylcerides
independently increase risk of heart disease, say the researchers.
They concluded, in the Journal of
Nutrition, 1998 (vol. 128, pp. 1144-1149), that it's more important for
overweight people to lose weight than change the fat composition of their
diets. And it appears that these people would benefit from substituting olive
or canola oil for saturated fat in their diet
For more information, contact
Jose M. Ordovas, (617)
556-3102, Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts University, Boston, MA
Back to
Contents
Few teens have eating habits that mirror the
Dietary Guidelines for Americans for fat and fiber. But those who do have more
nutritious diets overall. That's according to a survey of 319 teens who were
asked to recall what they had eaten in the prior 24 hours. Only one-third of
the students in the study had the more healthful eating pattern, including just
nine percent of non-white teens.
The teens who reported diets rich in fiber
and low in total fat consumed more vitamins and minerals and less total
cholesterol and saturated fat than their peers. Their diets included more iron,
zinc, calcium, folate and vitamin C, niacin, thiamin, riboflavin, magnesium,
phosphorus and vitamins A, B6, and B12. And the energy level was about the same
as those from most other groups, easing concern that low-fat, high-fiber diets
might be too low in energy for growing teens. The findings are reported in the
online issue of the Journal of Pediatrics: Pediatrics 2000 (vol. 105,
p. e21).
The teens were grouped into one of four
eating patterns: high-fat/high-fiber, high-fat/low-fiber, low-fat/low-fiber,
and low-fat/high-fiber. Food reports classified as low-fat met the dietary
guidelines that fat should provide no more than 30 percent of total daily
energy, while high-fat diets had levels of 40 percent or more. High-fiber diets
provided at least 20 grams of fiber and met the "age plus five"
recommendation for this age group. This recommends five grams of fiber plus one
gram per year of life through age 20. Low-fiber diets contained 15 grams or
less.
Individuals who met the dietary
recommendations for fat and fiber ate more whole-grain breads and ready-to-eat
cereals, fruit, salads, beans, vegetables, smaller portions and leaner cuts of
meat, skinless poultry, low-fat dairy products, and few fried and high-fat
foods.
For more information, contact
Theresa Nicklas, (713) 798-7087,
Children's Nutrition Research Center at
Baylor College of Medicine, Houston, TX
Back to
Contents
Each year, 180,000 new breast cancer cases
are diagnosed in U.S. women. Preliminary findings with rats suggest that adding
whey or soy protein to the diet may help guard against breast cancer.
Researchers compared the protective effects
of soy protein and whey protein against chemically induced tumors in the
milk-producing glands of rats. The test ratsa major animal model for
breast cancergot one of three diets, each with a different protein: a
control diet containing the major milk protein casein; a diet made with soy
protein isolate; or a diet with processed whey protein. Whey is a class of
minor proteins found in milk.
All rats in the control group developed at
least one tumor. But soy protein cut the rate by nearly one quarter, with 77
percent developing at least one tumor. Whey protein cut the rate nearly in
half; only 54 percent of the rats eating whey protein had tumors. And among the
whey group, the animals that developed mammary cancer had fewer and smaller
tumors than control rats, the researchers reported in Cancer, Epidemiology,
Biomarkers and Prevention, 2000 (vol. 9, pp. 113-117). They have filed a
patent on the whey compound.
For more information, contact
Thomas M. Badger, (501)
320-2785, Arkansas Children's Nutrition
Center, Little Rock, AR
Back to
Contents
Our body cells are constantly barraged with
chemical signals that pester them to respond. Miraculously, they do a pretty
good job of filtering out the "noise" and staying on purpose. But
some cells lose the ability to regulate these signals, and they react before
they should. Researchers now believe this loss contributes to chronic diseases,
such as cancer and heart disease. For example, if an order to divide gets
"heard" by too many cells, it could lead to unrestrained growth, as
in cancer or an overactive immune system.
Test-tube studies more than a decade ago
showed that a phytonutrient in soy foodsgenisteindampens
communication from the cell's surface to its interior. Now, an ARS study gives
the first evidence of this dampening effect in an animal.
For four weeks, researchers fed young rats
diets containing soy protein with high or low levels of genistein. Then they
measured how the animals' blood platelets responded. Platelets are quite
sensitive to outside signals and so are a good model for studying cell
signaling. In three different tests, the platelets from the animals receiving
the high-genistein diet showed less response to such signals, the researchers
reported in the Journal of Nutritional Biochemistry, 1999 (vol. 10, pp.
421-426).
Japanese diets, on average, contain about 10
times more soy than North American diets, and the Japanese have a lower
incidence of cancer and heart disease. The genistein-rich diet in this study
had the equivalent of twice the average Japanese genistein intake. The
genistein-poor diet contained the equivalent of the U.S. intake of soy. Tofu,
tempeh, and miso are some soy foods rich in genistein and other isoflavones.
For more information, contact
Norberta W. Schoene, (301)
504-8388, Nutrient Requirements
and Functions Laboratory, Beltsville, MD
Back to
Contents
A new study to define the antioxidant needs
of people with spinal cord injuries should also help clarify the nutrient
requirements of other, less severely injured individuals. The investigation,
apparently the first of its kind, will determine whether paralyzed people need
more antioxidant nutrients, such as vitamins A, C, and E, or
beta-carotenea compound that the body uses to make vitamin A. The
findings could also be applicable in determining the antioxidant requirements
of people who have injuries that leave them sedentary for months at a time or
who are gradually losing their mobility because of worsening arthritis, for
example.
ARS and University of California at Davis
scientists aim to work with 75 northern California adults with spinal cord
injuries to learn about their eating habits and to test their antioxidant
levels. The findings may help paralyzed people live longer and healthier lives.
Right now, Americans with spinal cord injuries live only about 80 percent as
long as their peers. Very little research has been done on the special nutrient
requirements of those with paralysis. Gunshot wounds and car, motorcycle, or
swimming pool accidents are among the leading causes of spinal cord injuries in
the United States today. The Paralyzed Veterans of America Spinal Cord Research
Foundation, Washington, DC, is funding part of the study.
For more information, contact
Betty J. Burri, (530) 752-4748,
Western Human Nutrition Research
Center, Davis, CA
Back to
Contents
A little extra cholesterol in our diets may
render the "bad" LDL cholesterol in our bloodstream more susceptible
to oxidation. That's what happened to the LDL from a group of older men and
women in a study reported in Atherosclerosis, 2000 (vol. 149, pp.
83-90). And that's not good: Evidence suggests that oxidized LDL cholesterol is
more apt to provoke the plaques that build up in arteries and increase risk of
heart attack and stroke.
The researchers designed 30-percent-fat diets
that differed only in the type of fat. One was rich in polyunsaturated fat from
corn oil; the other was rich in saturated fat from beef tallow. Otherwise, the
foods were identical. And by adding extra cholesterol to each dietranging
from around 220 to 330 milligrams, depending on the volunteer's total calorie
intakethey approximately doubled the diets' cholesterol content.
Thirteen men and women between the ages of 46
and 78 ate each of four diets: the corn oil with and without extra cholesterol
and the beef tallow with and without extra cholesterol. The type of fat didn't
significantly affect the susceptibility of the volunteers' LDL to oxidation in
a test-tube assay. But the extra cholesterol increased oxidation susceptibility
by 28 percent during the corn oil diet and 15 percent during the beef tallow
diet.
The volunteers began the study with
moderately elevated LDL cholesteroleach having levels greater than 130
milligrams per deciliter. Adding the extra dietary cholesterol prompted a
further rise in their total as well as their LDL cholesterol, regardless of the
type of fat in the diet. The researchers concluded that the current
recommendation to limit dietary cholesterol is both valid and prudent.
For more information, contact
Alice H. Lichtenstein, (617)
556-3127, Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts University, Boston, MA
Back to
Contents
An explosion of "super-sized" kids
has American health professionals clamoring for improved obesity-screening
tools. But preliminary findings from a large-scale study suggest the body mass
index (BMI) can produce inaccurate results if factors such as age, sex,
maturity, ethnic background, and physical activity are not considered.
The study compared the results of two obesity
indexes, the BMI and percent body fat (%Fat), in an ethnically diverse
population of 979 boys and girlsages 3 to 18. One out of six children in
the study who had a BMI in the normal range had an unhealthy level of body fat.
And one out of four with a BMI in the at-risk-to-obese range had a body-fat
level that was normal, the researchers reported in the American Journal of
Epidemiology, 1999 (vol. 50, pp. 939-946). The %Fat was determined with a
special instrument called DXA .
Two basic assumptions regarding body
composition lead to inaccuracies when the BMI is used as a one-size-fits-all
screening tool for fatness. One is that individuals who have a BMI within the
normal range have an average amount of body fat. The other is that every ounce
of body weight over the standard weight for height is fat.
These assumptions generated the most errors
for children with BMI values in the gray area between normal weight and
overweight, which is a BMI between 18 and 20 for most ages. Body fat in the
study children in this BMI range varied from 10 to 40 percent. Males with
body-fat levels over 25 percent and females with levels over 30 percent are
generally considered obese.
Relying on BMI alone risks the possibility
that kids who need some type of intervention to improve their physical activity
and eating habits will fall through the cracks. Of equal concern is the risk of
mislabeling 25 percent of high-BMI children as at-risk or overweight, despite
their normal body-fat percentage, the researchers caution.
For more information, contact
Kenneth Ellis, (713) 798-7131,
Children's Nutrition Research Center at
Baylor College of Medicine, Houston, TX
Back to
Contents
Ethnic differences in glucose metabolism
might help explain why Mexican-Americans are two to three times more likely to
suffer from diabetes than their European-American counterparts. Researchers
have found that one of the body's metabolic responses to insulinwhich is
to minimize the liver's conversion of glycogen into glucoseis
significantly reduced in Mexican-Americans. Glycogen is the storage form of
glucose in the liver and muscle tissues.
The researchers believe this could be one of
the earliest markers of insulin resistance in Mexican-Americans and a defect
that could be contributing to the high rates of type-2 diabetes in this group
as a whole. Insulin resistancethe body cells' insensitivity to the action
of insulinis responsible for 90 to 95 percent of all diabetes cases in
Mexican-Americans.
The study involved six Mexican-American males
and six European-American males matched for age and body mass index. All were
healthy and showed no sign of insulin resistance on a glucose tolerance test,
and none had close relatives with diabetes. Their liver glucose production was
monitored while fasting and during a six-hour feeding period designed to test
the liver's ability to minimize its own glucose production when food is
ingested.
Although no significant differences were
noted between the two groups during the fasting studies, important differences
appeared when the men were fed. In the European-American men, both of the
liver's glucose-producing pathways responded to insulin as
expectedquickly shutting down to a trickle. But in the Mexican-Americans,
the pathway that converts glycogen to glucose took much longer and required
higher levels of insulin to significantly reduce glucose production, the
researchers reported in the American Journal of Physiology (Endocrinology
and Metabolism), 1999 (vol. 277, pp. E905-914).
Knowing which pathway is affected
could help scientists identify the causesuch as a unique
generesponsible for this disregulation. This might lead to therapies and
early lifestyle interventions that help at-risk Mexican-American children
before the clinical symptoms of insulin resistance and diabetes appear later in
life.
For more information, contact
Farook Jahoor, (713) 798-7084,
Children's Nutrition Research Center at
Baylor College of Medicine, Houston, TX
Back to
Contents
Tomorrow's tortillas, if made
with a unique corn from ARS research, may help reduce iron-deficiency anemia.
That could be a boon in developing countries where corn-based foods are a part
of nearly every meal and in developed nations where iron deficiency is also
common. The novel corn has about 66 percent less phytic acid, or phytate, than
most common varieties. Phytic acid is thought to reduce the body's ability to
absorb certain nutrients, like iron.
In a study of 14 men, scientists
from the Institute of Nutrition of Central America and Panama and from the
University of California's Berkeley and Davis campuses showed that iron
absorption was about 50 percent greater if the men ate tortillas made from
flour of the low-phytic-acid corn, compared with normal corn flour. The
findings are reported in the American Journal of Clinical Nutrition,
1998 (vol. 68, pp. 1123-1127).
Now, University of Colorado
researchers are leading an investigation of the effects of the corn on zinc
absorption in a study with Guatemalan villagers.
For more information, contact
A. Victor Raboy, (208) 397-4162, ext.
15, Small Grains and
Potato Germplasm Research Unit, Aberdeen, ID
Back to Contents
In late summer, up to 28 percent of cattle
entering processing plants may carry with them strains of the E. coli
bacterium that causes food poisoning in humans, according to a recent
study. Improved laboratory methods allowed the scientists to ferret out the
microbe and detect this prevalence level, which is higher than previously
reported.
But the research also showed that normal
processing procedures can reduce the incidence of E. coli 0157:H7 on
beef carcasses to less than 2 percenteven in the peak contamination
season of July and August. The study, reported in the Proceedings of the
National Academy of Sciences, 2000 (vol. 97, pp. 2999-3003 ), included
examination of E. coli shed in the feces of live cattle, as well as
microbes on beef carcasses in commercial processing plants.
During the summer E. coli peak, 28
percent of the live cattle entering the processing plants were actively
shedding E. coli 0157:H7 in their feces. Eleven percent of hide surfaces
were also contaminated with the bacterium. After processing was complete, only
six of 330 carcasses, or 1.8 percent, showed some level of
contamination.
For more information, contact
Danny B. Laster, (402)
762-4109, Roman L. Hruska U.S. Meat Animal
Research Center, Clay Center, NE
Back to
Contents
|