BHNRC Success Stories
GOOD NUTRITION COULD HELP PREVENT BAD VIRUSES
Once again, a relatively benign virus has mutated into a nasty pathogen in laboratory mice that were raised on diet deficient in selenium--a potent antioxidant. This time the mutations occurred in a common influenza virus--a strain isolated in Bangkok in 1979. And the mutations persisted in mice fed ample selenium, causing a much more severe case of flu than the original strain.
The discovery, according to the researchers, demonstrates a unique mechanism by which viruses can mutate and points to the importance of antioxidant protection against viral diseases. The selenium level in the study's deficient diet was one-sixtieth that of the adequate diet.
Seven years ago, UNC virologist Melinda A. Beck and BHNRC nutritionist Orville Levander reported that a lesser known obscure virus--a strain of coxsackie--mutated from "Jekyll" to "Hyde" in selenium-deficient mice. This April, the two researchers and their colleagues reported that the Bangkok strain of influenza virus also caused a much more severe case of flu in selenium-deficient mice than in animals given adequate selenium in their feed. In today's report, they explain why.
Twenty-nine bases in a normally stable section of the viral genome had mutated in the selenium-deficient mice. By contrast, there were no mutations in the same area of the viral genome from selenium-adequate mice. It shows that the host's nutrition can have considerable influence on the virulence of viral pathogens and that the virulence persists in well-nourished animals and, presumably, people.
The findings have global implications, according to Dr. Levander. While Americans generally get the recommended dietary levels of selenium, there are pockets of selenium deficiency around the world that might be generating harmful mutations in a number of viruses. And viruses know no boundaries.
Diet, Genomics and Immunology Laboratory
Back to Top
LOW-FAT FOODS CAN HELP LOWER FAT INTAKE - BUT IT'S NOT GUARANTEED
Switching to reduced-fat or fat-free foods--like lean meats, low-fat desserts or skim milk--can help cut your fat intake to the recommended 30 percent of total calories or less. But you need to watch your fat intake from other foods as well, an Agricultural Research Service study shows.
BHNRC nutritionist Shanthy Bowman and former USDA deputy undersecretary Eileen Kennedy analyzed data from the 1996 USDA nationwide food consumption survey to determine the impact of reduced-fat products on total fat intake. For comparison, they divided a sample of 1,731 adults into two groups-those who met the recommended fat intake and those who exceeded it.
While the majority of adults who exceeded the fat recommendation either didn't consume reduced-fat products on the survey day or ate only one or two, some of them ate three or more such foods. They simply got too many fat calories from the rest of their diet.
Among the group that met the recommended fat intake, a larger percentage consumed reduced-fat products, showing that these foods can be helpful in reducing fat intake.
One doesn't have to make many reduced-fat substitutions, according to Bowman. Just one or two will do, as long as people don't add the fat back with other food choices. Naturally low-fat fruits and vegetables are good choices because they are packed with fiber and nutrients.
The analysis also showed that consuming reduced-fat products was associated with a more varied and nutritious diet-among both groups. Men and women who chose reduced-fat products- especially those who ate three or more daily-got more vitamin A, carotene, folate, calcium and iron than those who didn't. Nonusers tended to substitute carbohydrates and carbonated sodas to replace fat.
Not surprisingly, the men and women who met the recommended fat intake consumed fewer calories than those who exceeded it-400 to 500 less calories on average. And their body mass index (BMI) tended to be lower, especially among the women.
Community Nutrition Research Group
Back to Top
SELENIUM DEFICIENCY INCREASES SEVERITY OF FLU VIRUS IN MICE
If young mice are given a diet deficient in selenium and subsequently exposed to a human influenza virus, they get a more severe case of flu than animals fed adequate amounts of this essential trace element.
That's the finding of a collaborative study by researchers at the University of North Carolina (UNC) in Chapel Hill, Nestle Research Center in Lausanne, Switzerland, and the Beltsville Human Nutrition Research Center. And it follows the pattern seen in earlier studies with a lesser known virus. This indicates that a selenium deficiency can increase the virulence of a variety of viruses.
The research indicates that the mice getting selenium-deficient diets developed significantly more lung pathology than the animals getting ample selenium. The deficient mice had significantly more inflammation in their lungs, and the inflammation lasted much longer.
Selenium is a critical part of a major antioxidant enzyme that humans and animals produce to protect delicate cellular components against damage from oxygen free radicals. Americans get ample selenium in their diets, according to BHNRC nutritionist Orville A. Levander. Good sources include Brazil nuts, whole grain products and meat. But deficiencies can occur in parts of China, New Zealand other nations where agricultural soils lack this element.
Levander collaborated with study leader Melinda A. Beck, a viral immunologist at UNC's departments of Pediatrics and Nutrition, on this and the earlier studies. The researchers suspect that the influenza virus mutated to a more virulent form in the selenium-deficient animals because these animals lack antioxidant protection from the selenium-containing enzyme--glutathione peroxidase.
In 1995, the researchers reported that a normally harmless coxsackie virus mutated into a heart- damaging pathogen in selenium-deficient mice but not in selenium-adequate mice. Beck and collaborators are now looking for mutations in the influenza virus genome.
Diet, Genomic and Immunology Laboratory
Back to Top
MORE POTENT CHROMIUM SUPPLEMENT ON THE WAY
Numerous studies have demonstrated that taking extra chromium daily--in the form of a supplement--may improve glucose tolerance in people whose blood sugar levels range from slightly elevated to full-blown diabetes. Now, the BHNRC is applying for a patent on a new chromium formulation that people absorb into the bloodstream better than anything on the market.
Typical Western diets barely supply the new adequate intake for chromium--35 micrograms (mcg) daily for men, 25 mcg for women. And high sugar intakes, trauma and hard exercise can increase our chromium excretion. Because the mineral improves insulin function, a shortfall can impair the cells' ability to remove excess sugar from the blood stream.
The new BHNRC formulation is a complex of chromium and the essential amino acid, histidine. It is absorbed at least 50 percent better than chromium picolinate, according to its developer, Richard Anderson, a scientist at the Beltsville Human Nutrition Research Center. The picolinate formulation, patented by ARS nearly three decades ago, is the best absorbed and most popular chromium supplement sold today.
In tests at the BHNRC, men and women absorbed an average 3.1 mcg of chromium from the chromium-histidine complex, compared with 1.8 mcg from chromium picolinate, 0.4 mcg from chromium chloride and 0.2 mcg from chromium polynicotinate. The latter two formulations are also popular supplements.
The new complex should pose little or no toxicity as long as people understand that chromium itself can be toxic in doses many times higher than those found in supplements. In fact, people should benefit from the extra histidine because it is one of the required amino acids that the body doesn't manufacture.
In studies worldwide, supplemental chromium has improved blood sugar levels or other symptoms in people with glucose intolerance, type 1 and type 2 diabetes, steroid-induced diabetes, and gestational diabetes. However, chromium supplements won't help people who have high blood sugar in spite of getting adequate dietary chromium.
Diet, Genomics and Immunology Laboratory
Back to Top
WHAT WE EAT IN AMERICA - RESULTS FROM USDA'S FOOD CONSUMPTION SURVEY
American diets are changing in a number of ways according to data from the 1994-96 Continuing Survey of Food Intakes by Individuals, popularly known as "What We Eat in America."
Consumption of dietary fat has continued a downward trend. In 1994-96, fat accounted for 33 percent of total calories compared with 40 percent in the late 1970's. Despite this decrease, in 1994-96 only about one-third of adults met the 30 percent or less of calories from fat recommended by nutrition experts.
Vegetable and fruit consumption has remained about the same despite recommendations to eat more. Vegetable consumption has decreased slightly and fruit consumption has risen only about 20 percent since the late 1970's. In 1994-96, only a little over half of the population reported eating fruit on any given day. The biggest change in food consumption has been in grain products. Consumption of grain mixtures--such as lasagna and pizza--increased 110 percent since the late 1970's. Snack foods and ready-to-eat cereals have increased also.
Among young children, consumption of fluid milk has decreased by 16 percent since the late 1970's, while consumption of carbonated soft drinks has increased by 16 percent. Consumption of noncitrus juices, including grape- and apple-based mixtures, rose by 280 percent.
The percentages of individuals who eat away from home on any given day has increased by a third. In 1994-96, 57 percent of Americans ate away from home on any given day. Foods eaten away from home accounted for more than 25 percent of intakes of total calories and most nutrients. Beverages, particularly carbonated soft drinks, were the most popular food item consumed outside the home.
These results are based on personal interviews with about 16,000 Americans of all ages and incomes. The figures are average intakes, so many Americans either exceed or fall below the average. The data are used to make public policy decisions related to food safety, food fortification, food assistance, and nutrition education programs and also for research, food production and marketing, and many other areas.
Food Surveys Research Group
Back to Top
CAROTENOIDS SHOW THEIR REAL COLORS
Dark green and deep yellow vegetables and tomatoes are good sources of the carotenoids-- beta-carotene, lutein and lycopene, a preliminary study suggests.
Researchers wanted to know if people could increase their blood levels of these carotenoids--the red, yellow and orange pigments in fruits and vegetables--by eating acceptable portions of carotenoid-rich vegetables. So 12 volunteers lunched daily on five servings of cooked kale and sweet potato and washed it down with tomato juice--together providing 10 times more than typical U.S. carotenoid intakes.
The veggie lunches more than doubled blood levels of beta-carotene and increased lutein by 67 percent and lycopene by 26 percent. Sweet potato is rich in beta-carotene, while kale and tomato are top sources of lutein and lycopene, respectively. As potent antioxidants, these carotenoids are thought to contribute to the lower rates of heart disease, cancer and other diseases of aging among populations that eat a lot of fruits and vegetables.
Principal Investigators: Tim R. Kramer and Beverly Clevidence, Food Componets and Health Laboratory
Back to Top
FRIENDLIER FOOD TABLES
Its now possible to take in over 6,000 foods at one sitting without gaining a pound. Just download the new USDA Nutrient Database for Standard Reference (SR13) from the Internet. It's free of charge. This release of the food composition tables lists values for more than 80 food components--such as vitamins, minerals, lipids, amino acids, fiber and energy (calories)--in about 6,200 foods grouped into 23 categories. It replaces SR12, issued in March 1998, as well as the printed publication--USDA Handbook No. 8.
In the latest version, laboratory nutritionists have:
- added a couple hundred new items and updated a number of other items.
- Incorporated supplementary data on Australian lamb, previously released as a separate table,
- Added values for vitamin D in selected foods. Data are primarily on selected dairy foods, breakfast cereals, meats, and seafood. These values include data from the "Provisional Table on the Vitamin D Content of Foods" (Weihrauch and Tamaki 1991)
The nutrient database is a major source of food composition data for epidemiological researchers as well as food and nutrition professionals, and serves as the foundation for most commercial nutrient database programs. SR13 continues the relational format adopted with SR11. Users with relational database management software--such as Paradox, Access, Dbase, and others---can retrieve information and generate their own reports. Nutrient data in SR13 can be retrieved from the Internet on the Nutrient Data Laboratory Home Page. The on-line search tool for locating the nutrient values of individual foods has been updated to report the new values. Also included with this release are tabular reports of each food item in the database arranged by food group. These reports can either be printed, searched or copied to user's computers Internet the internet.
Nutrient Data Laboratory
Back to Top
CHROMIUM - THE GOOD FOOD CONTAMINANT
Cereals, particularly bran cereals, are among the top sources of chromium, according to state-of-the art analyses of 40 foods. Of the seven cereals analyzed, five contained between 10 and 20 percent of the minimum suggested chromium intake in a one- or two-ounce serving. But a slice of whole wheat bread or an ounce of toasted wheat bran provides only about one percent of the minimum, suggesting that much of the chromium in foods is contributed by other factors and is not intrinsic to the food itself. The high levels in cereals probably are inadvertently added during fortification with other minerals or vitamins.
Chromium also may be introduced as a result of processing or handling. One cup of canned mushrooms had more than 10 percent of the suggested minimum chromium intake, as did one teaspoon of cocoa powder. But chocolate syrup had only half as much per serving. Canned whole tomatoes and pineapple slices scored highest in chromium content in this study, with one cup providing 33 to 43 percent of the minimum suggested intake. Many canned and processed foods are prepared in stainless steel vessels, which have a high chromium content. This appears to be a case of good contamination because the body can convert inorganic chromium to a usable form.
For these analyses, the researcher selected 20 frequently consumed foods and 20 other foods, including cereals, condiments and snack foods, that were expected to have higher chromium levels. There are no comprehensive data bases on the chromium content of foods. And, until a decade ago, analytical methods for detecting chromium in foods were quite unreliable. Recent advances in graphite furnace atomic absorption spectrometry, used in this study, provide a rapid and highly accurate method of detecting the small amounts of chromium in foods.
Principal Investigator: Nancy J. Miller-Ihli, Food Composition and Methods Laboratory
Back to Top
SELENIUM DEFICIENCY PROMPTS VIRUS TO MUTATE
A human virus normally harmless in laboratory mice mutated into a heart-damaging pathogen when the animals were raised on a diet devoid of the essential element selenium. And, once mutated, the virus continued to damage hearts--even in mice that got ample selenium in their feed. The findings are the first indication that a nutritional deficiency can cause a virus to mutate to a more virulent form. And its importance is not limited to nutritionally-deprived populations, say researchers with the University of North Carolina and ARS who collaborated on the studies. In theory, one selenium-deficient person or animal could produce a new family of virus mutants that could cross species and spread worldwide, causing disease even in well-nourished people.
ARS researchers supplied the nutritional expertise and diets. UNC researchers found six sites on the coxsackie B3 virus genome that were permanently altered after it had spent time in selenium-deficient mice. Coxsackie viruses, as a group, infect more than 20 million people in this country annually, producing a range of maladies from sore throat and cold symptoms to inflammation of the heart muscle. About 10 percent of infected people develop serious diseases, including heart muscle inflammation.
Other nutritional deficiencies can also cause viral mutations, it appears. UNC researchers are now analyzing the genes of coxsackie B3 virus that damaged hearts in vitamin-E-deficient mice. They expect to find the same alterations as with selenium deficiency. Both nutrients serve as antioxidants in the body. If such mutations occur in other RNA viruses, they may help explain the many new strains of influenza virus arising in China, which has widespread selenium-deficient areas.
Principal Investigators: Orville A. Levander, Diet, Genomics and Immunology Laboratory and Melinda A. Beck, University of North Carolina, Chapel Hill, NC
Back to Top
DIETS THAT DEFLATE HIGH BLOOD PRESSURE
People with high blood pressure would benefit from redesigning their diet in addition to avoiding salt. That's the message from the multi-center DASH study recently reported in the New England Journal of Medicine (vol. 336 (16): 1117-1124). Adding several servings of fruits and vegetables and a few low-fat dairy foods to a reduced-fat diet significantly lowered blood pressure in African-American and Caucasian men and women.
ARS dietitians helped design the menus used to feed nearly 460 volunteers at four centers around the country. They also prepared all meals for The Johns Hopkins University in Baltimore. One third of the volunteers got a "typical" U.S. diet--low in fruits, vegetables and dairy products, with 37 percent of calories from fat. This group served as controls. Another third ate the same amount of fat but with eight to 10 servings of fruits and vegetables daily. The third group got a low-fat diet with the extra fruits and vegetables plus three servings of dairy products. This combination diet had 27 percent of calories as fat with only 6 percent saturated fat.
After eight weeks on this combination diet, systolic pressure dropped an average 11.4 points and diastolic pressure was down 5.5 points in the volunteers with high blood pressure. That's about what can be achieved with a single medication. The average drop for all participants, including those with normal blood pressure, was also significant--5.5 and 3 points, respectively.
The combination menu was designed to increase intakes of fiber and three minerals important for blood pressure regulation--potassium, magnesium and calcium. Bananas, dried fruits and melon pieces, for instance, supplied extra potassium, which totaled 4,700 milligrams daily. Spinach, dried fruits, broccoli and scallions helped raise the magnesium intake to 500 mg. daily. And low-fat dairy products brought calcium intake up to 1,200 mg. Fiber intake was 30 grams daily. Salt was held at 3,000 mg. for all diets. Menus for all three diets are posted on the Web at http://dash.bwh.harvard.edu.
Human Studies Facility
Back to Top
|
Printable Version
E-mail this page
