Plant-Rich Diets Have Antioxidant Power

By Judy McBride
October 15, 1998

A diet rich in leafy green and yellow-orange vegetables and fruits, whole grains, raisins and nuts supplies plenty of antioxidants—substances that prevent and reduce oxidation in the body's cells. Oxidation in cells appears to play a role in aging and chronic diseases. When 12 female volunteers in a study switched from a typical "Western" refined-food diet to a plant-rich diet, their bodies relaxed their natural defenses by producing smaller amounts of two enzymes that protect cells against oxidative damage.

Agricultural Research Service scientists collaborated on the antioxidants study conducted at the private SPHERA Foundation in Los Altos, Calif. ARS is the U.S. Department of Agriculture's chief research agency.

To compare antioxidant power of the two diets, Leslie Klevay and Sandra Gallagher with ARS' Grand Forks, N.D., Human Nutrition Research Center looked at changes in the two enzymes. One, a copper-containing enzyme called superoxide dismutase, dropped by two-thirds when the women ate the plant-rich diet. A selenium-containing enzyme, glutathione peroxidase, dropped by one-third.

For four weeks, the volunteers consumed all the white bread, pasta, pastry, snack foods, convenience foods, meat, fish, poultry, eggs and dairy their hearts desired. They limited fruits and vegetables to two servings a day, with no leafy green and yellow varieties allowed.

Then, for four weeks, the volunteers ate at least six servings daily of green and yellow fruits and veggies. They switched to whole grain bread and ate as many other whole grains and legumes as they wanted. They also downed two tablespoons each of almonds, hazelnuts, pecans and sesame oil (tahini); a tablespoon of wheat germ oil for cooking or dressing; 4-1/2 ounces of raisins; one cup of ginger tea and two cups of green tea. Fried foods, refined products and reduced-calorie and fat-free products were forbidden. Eggs were allowed, but meat, fish and poultry were limited to 3 ounces per week. Dairy products were no more than 1 percent fat.

A story about the research appears in the October Agricultural Research magazine. The story also is online at:

/is/AR/archive/oct98/diets1098.htm

Scientific contact: Leslie M. Klevay, ARS Grand Forks Human Nutrition Research Center, Grand Forks, N.D., (701) 795-8454, fax (701) 795-8395, lklevay@gfhnrc.ars.usda.gov.