Not all fruit antioxidants behave alike, USDA

As part of the study, led by Ronald Prior, researchers looked at the antioxidant status of volunteer participants at the Arkansas Children's Nutrition Center after the consumption of different fruits. The results point to some of the different factors that may affect how antioxidants work in the body and their effectiveness. The effectiveness of antioxidants suddenly became controversial in February following a meta-analysis that linked the compounds to increased mortality. A meta-analysis of 68 randomized trials with antioxidant supplements published in the Journal of the American Medical Association in February reported that vitamins A and E could increase mortality by up to 16 percent. The findings were widely publicized in mainstream media and trade associations, and industry advocates found themselves in a position of having to clean up after the bad publicity. Critics again pointed the finger at the ineffectual study model used to arrive at the conclusions - a case of comparing apples to oranges, they said. As part of the US Department of Agriculture's study, nutritionists from the Agricultural Research Service assessed antioxidant capacity (AOC) measured as Oxygen Radical Absorbance Capacity (ORAC). Participants were recruited for five different studies conducted at different institutes. They were given blueberries, grapes, kiwifruit, strawberry, cherry and dried plums. The researchers found that despite the high antioxidant content of plums, the fruit did not in fact raise the AOC plasma levels in participants. This was attributed to the fact plums contain chlorogenic acid, a phytochemicals not easily absorbed by humans. The results for blueberries, which are lauded for their high antioxidant content, were somewhat more surprising. The nutritionists needed significantly large servings - a half-cup serving of the berries - in the study in order to elevate AOC levels. Consumption of grapes and kiwi in the study boosted plasma AOC levels, but the authors said they were not certain which compounds were responsible for this. "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,"​ concluded the authors. "However, without further long term clinical studies, one cannot necessarily translate increases in plasma AOC into a potential decreased risk of chronic degenerative disease."​ Source: Prior, Ronald L. et al. "Plasma antioxidant capacity changes following a meal as a measure of the ability of a food to alter in vivo antioxidant status."​ Journal of the American College of Nutrition. Vol. 26, No. 2, 170-181 (2007).