An extra 200 milligrams of vitamin E daily may help reduce infections in older people, but bigger doses of the vitamin don't mean bigger benefits. In a recent ARS study, men and women over age 65 who took daily vitamin E supplements had improvements in the immune system's response to foreign antigens--substances that prompt the body to produce antibodies.

The immune system declines with aging, contributing to increased infections. Until now, few nutritional interventions have boosted older people's immune response. The 80 volunteers in the study took either 60, 200 or 800 mg of vitamin E--or a look-alike placebo--each day for 4-1/2 months. Then they were given a standard test, called DTH, that measures the body's reaction to seven antigens injected into the skin. The DTH test indicates how well immune-system cells called T cells "remember" antigens they have seen before and how to respond to them. Compared with the placebo group, the group getting 200 mg daily--equivalent to 200 International Units--had a 65 percent increase in DTH response. Those taking 800 mg had a 49 percent increase, the researchers reported in the Journal of the American Medical Association (vol. 277, pp. 1380-1386).

The 200-mg group also produced the most antibodies to three vaccines administered after the supplemental period. For example, their antibodies to hepatitis B virus were sixfold greater than those in the placebo group. The findings suggest that 200 mg is a threshold level, and that higher levels confer no extra benefit.

That vitamin E enhances the immune system is further supported by an animal study these researchers reported in the Journal of Infectious Diseases (vol. 176, pp. 273-276). Older mice receiving high doses of vitamin E suppressed influenza virus far better than those getting the recommended level of vitamin E. Until now, only food restriction has subdued this virus in animal studies. And that's not practical for people.

For more information, contact Simin Nikbin Meydani, (617) 556-3129, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA; s_meydani_im@hnrc.tufts.edu

Counting Calories More Precisely

Can you trust the number of calories per serving on the label of a frozen fruit pie or vegetable medley? A recent ARS study indicates that values listed for fiber-containing foods could be more accurate if food companies used an equation developed in 1991 by a British researcher. Because some calories in foods don't get digested and absorbed, food manufacturers estimate the available calories in each product. ARS researchers found that the 1991 Livesey equation is a better predictor of this so called "metabolizable energy" than some equations now sanctioned by the U.S. Food and Drug Administration. They also found that the amount of total dietary fiber can be used in the equations interchangeably with the amount of insoluble fiber, known chemically as NDF. Each produces essentially the same calorie value.

The researchers tested nine diets on 17 volunteers for two weeks at a time. They measured how much carbohydrate, fat, protein, fiber and energy (calories) the volunteers used from the diets--nine combinations of low, medium and high fat with low, medium and high fiber. Dieticians increased the fiber intake by adding breakfast cereal, carrot and celery sticks, tossed salads, canned and fresh fruits, cookies, nuts and sunflower seeds to the menu.

Overall, increasing the fiber intake decreased the digestion and absorption of both fat and protein, the researchers reported in the Journal of Nutrition (127, pp. 579-586). As a result, available calories decreased as fiber increased. Based on actual measurements, the researchers estimate that if U.S. men doubled their daily fiber intake from an average 18 grams to 36 grams--the highest amount used in this study--they would absorb about 130 fewer calories per day. For women, doubling fiber intake from 12 to 24 grams a day would reduce absorption by 90 calories.

For more information, contact David J. Baer, (301) 504-8719, Beltsville Human Nutrition Research Center, Beltsville, MD; baer@bhnrc.arsusda.gov

Spinach 'n Strawberries--An Antioxidant Recipe

Eating a half pound of strawberries or spinach can be just as effective as taking a large dose of vitamin C in helping the human body defuse oxygen radicals that can damage cells. That's the latest finding from ARS research into the antioxidant capacity of fruits and vegetables. Last year, the researchers found strawberries and spinach to be high in total antioxidant capacity among 40 common fruits and vegetables they tested, using a highly sensitive chemical assay they developed.

Next, they wanted to find out whether those protective compounds could be absorbed by the human body in sufficient amounts to boost the blood's antioxidant profile. They analyzed the blood of eight women in their 60s and 70s before and after eating five test meals. Each woman first ate a control meal with a low antioxidant content. Then, over the course of two months, the researchers added either a strawberry extract, a spinach extract, red wine or 1,250 milligrams of vitamin C to the control meal. The strawberry and spinach extracts were consumed as drinks having the equivalent of 8 to 10 ounces of the produce.

Simply eating the control meal increased the antioxidants circulating in the women's blood up to 10 percent. The strawberry and spinach extracts boosted the antioxidant capacity another 20 percent. That's as much protection as the women got from taking the vitamin C. Red wine was somewhat less effective, boosting antioxidant capacity by 15 percent above the control level. Some but not all of the antioxidant boost was due to vitamin C and uric acid--an antioxidant made by the body, the researchers found. They conclude that other antioxidants--probably polyphenols--are being absorbed from the fruits and vegetables.

For more information, contact Ronald L. Prior or Guohua Cao, (617) 556-3311/-3141, USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA; prior_us@hnrc.tufts.edu; cao_am@hnrc.tufts.edu

The Down Side of Calorie Cutting

Weight-loss diets can hinder natural killer cells--an important part of the immune system--even if the diets provide healthful meals. A new ARS study confirms earlier findings by other scientists about changes in killer cell activity in fasting or malnourished people. Eight healthy women, age 28 to 41, cut their calorie intake in half for 15 weeks. The researchers found about a 20 percent decrease in the activity of killer cells, which help protect the body against viruses and tumors. They measured this activity with a standard laboratory test in which natural killer cells isolated from blood samples were mixed with target cells. Target cells successfully attacked by the killer cells released a tracer element--a special form of chromium--that the researchers could then measure.

Physicians, dietitians and other healthcare professionals could use the information to improve weight loss programs by minimizing unwanted effects on the immune system. Longer and more restrictive periods of dieting could further undermine the killer cells, scientists caution. An estimated 40 percent of American women and 25 percent of American men are trying to lose weight. Obesity increases risk of diabetes, cardiovascular disease, hypertension and other illnesses.

For more information, contact Darshan S. Kelley, (415) 556-4381, Western Human Nutrition Research Center, San Francisco, CA; dkelley@whnrc.usda.gov

Citrus Squeezed for Cancer Fighters

A new technique makes possible--for the first time--large-scale extraction of useful natural compounds known as limonoid glucosides that show promise as cancer-fighting agents. ARS researchers identified the chemicals nearly a decade ago in oranges and other citrus fruits. At that time, food-industry interest centered on their role in reducing bitterness of citrus juices.

ARS scientists helped develop the new manufacturing technique with Japanese researchers. The Japanese group has test-marketed a fruit juice beverage with added limonoid glucosides. The team has applied for patent protection for their method of extracting the glucosides from citrus juice or the thick, dark brown material called citrus molasses. Citrus molasses comes from peels and other citrus waste, while the molasses familiar to consumers is produced during the refinement of raw sugar from sugarcane or sugar beets.

In the new method, the citrus juice or citrus molasses passes through a device lined with material that collects up to 100 percent of the desired compounds. Washing out the material with a solvent such as alcohol yields a purified liquid full of limonoid glucosides.

For more information, contact Shin Hasegawa, (510) 559-5819, USDA-ARS Process Chemistry and Engineering Unit, Albany, CA; shinh@pw.usda.gov

Dietary Choices Don't Reflect Knowledge

What we eat in America isn't necessarily what we think we should eat. That's the bottom line from ARS' most recent nationwide food consumption survey. Two-thirds of adults think it's very important to choose a diet with plenty of vegetables and fruits--as stated in one of the Dietary Guidelines for Americans. But their survey responses, collected in 1994-95, showed consumption of these foods has increased only slightly since the late 1970's. Fruit intake is slightly below the minimum two servings recommended in USDA's Food Guide Pyramid. Vegetable intake is only slightly above the minimum three servings. And, veggie consumption leans more to french fries than to the dark green and yellow vegetables associated with health benefits.

On the other hand, while grains form the base of the Food Pyramid, less than one-third of adults think eating plenty of breads, cereals, rice and pasta is very important. Yet, consumption of these foods has jumped more than 40 percent since the late 1970's.

Ninety percent of adults believe it's important to maintain a healthy weight. But 40 percent think they consume too many calories, and one-third are overweight. What's more, 28 percent of men and 44 percent of women report they rarely if ever exercise vigorously.

Sugar and salt/sodium consumption also doesn't follow beliefs. Eighty-five percent of adults agree with dietary guidelines that advise a diet moderate in sugars. But Americans daily consume an average 19 teaspoons of sugar that is added to their foods--by beverage and food processors or by consumers themselves. These 19 teaspoons account for 15 percent of our total calories for the population as a whole, and a considerably higher percent for adolescents.

As for sodium, men exceeded by two-thirds the recommended upper limit of 2,400 milligrams daily. That's from foods alone, not counting salt added at the table. Women's diets have less sodium than men's, but they still consume one-quarter more than the recommended limit from foods alone.

For more information, contact Linda E. Cleveland, (301) 734-8457, Beltsville Human Nutrition Research Center, Riverdale, MD; lcleveland@rbhnrc.usda.gov