Researchers from the US Department of Agriculture (USDA) measured the blood antioxidant capacity (AOC) of subjects in a series of five clinical trials, and found that consumption of antioxidant-rich foods blunted oxidative stress after a meal of rich in carbohydrates, protein, and fat.
"We have demonstrated that consumption of certain berries and fruits such as blueberries, mixed grape and kiwifruit, was associated with increased plasma AOC in the postprandial state and consumption of an energy source of macronutrients containing no antioxidants was associated with a decline in plasma AOC," wrote lead author Ron Prior in the Journal of the American College of Nutrition .
Oxidative stress has been linked to an increased risk of various diseases including cancer, Alzheimer's, and cardiovascular disease.
"Without further long term clinical studies, one cannot necessarily translate increased plasma AOC into a potential decreased risk of chronic degenerative disease," stated Prior and co-workers.
In order to determine if the meals containing the different fruit or berries increased the hydrophilic (water-soluble) or lipophilic (fat soluble) antioxidant capacity, measured as Oxygen Radical Absorbance Capacity (ORAC), the researchers conducted five clinical trials with six to ten subjects per experiment.
Blood samples from the subjects were taken pre- and post-prandially (before and after the meal).
The researchers report that neither dried plums nor dried plum juice altered either measure of antioxidant activity.
Blueberries or mixed grape consumption (12.5 and 8.6 millimole Trolox Equivalents (TE AOC), respectively) with the meal was associated with a increase in hydrophilic AOC.
Blueberries also increased the lipophilic AOC. Cherries, eaten with the meal and providing 4.5 millimoles TE AOC, increased the lipophilic, but not the hydrophilic, AOC.
A control meal, rich in the macronutrients - carbohydrates, protein and fat - consumed without antioxidants was found to result in a decrease of blood AOC, showing an increase in oxidative stress.
"It's not just what you eat but when you eat it that matters.
Phytochemicals in foods have varying degrees of bioavailability and generally are cleared from the blood 2-4 hours after they're eaten," said Prior.
"Ensuring that your body has a steady supply of antioxidant-rich foods can help combat oxidative stress throughout the day."
"It takes about 2.5 servings of antioxidant containing fruits and/or vegetables in a meal… to prevent oxidative stress following the meal.
The more calories you take in the more dietary antioxidants you need," he added.
The research was welcomed by the Wild Blueberry Association, a trade association of growers and processors of wild blueberries from Maine.
Susan Davis, nutrition advisor for the association advised: "Incorporate fruits and vegetables and other whole foods like grains and nuts into every meal to get the full phytochemical benefits you need to fight oxidative stress and inflammation." Affiliated research partners for the new study included the USDA Human Nutrition Research Center on Aging in Boston, Massachusetts, the USDA/ARS Western Human Nutrition Research Center at the University of California, Davis, and the Department of Food Science and Human Nutrition at the University of Maine.
Source: Journal of the American College of Nutrition Volume 26, Number 2, Pages 170-181 "Plasma Antioxidant Capacity Changes Following a Meal as a Measure of the Ability of a Food to Alter In Vivo Antioxidant Status" Authors:
R.L.
Prior, L. Gu, X. Wu, R.A. Jacob, G. Sotoudeh, A.A. Kader, R.A. Cook