X-Message-Number: 24707
Date: Fri, 24 Sep 2004 05:30:19 -0700 (PDT)
From: Doug Skrecky <>
Subject: surprise "antioxident" in apples

Free Radic Biol Med. 2004 Jul 15;37(2):251-8
The increase in human plasma antioxidant capacity after apple consumption
is due to the metabolic effect of fructose on urate, not apple-derived
antioxidant flavonoids.
 Regular fruit consumption lowers the risk of cardiovascular diseases and
certain cancers, which has been attributed in part to fruit-derived
antioxidant flavonoids. However, flavonoids are poorly absorbed by
humans, and the increase in plasma antioxidant capacity observed after
consumption of flavonoid-rich foods often greatly exceeds the increase in
plasma flavonoids. In the present study, six healthy subjects consumed
five Red Delicious apples (1037 +/- 38 g), plain bagels (263.1 +/- 0.9 g)
and water matching the carbohydrate content and mass of the apples, and
fructose (63.9 +/- 2.9 g) in water matching the fructose content and mass
of the apples. The antoxidant capacity of plasma was measured before and
up to 6 h after food consumption as ferric reducing antioxidant potential
(FRAP), without or with ascorbate oxidase treatment (FRAPAO) to estimate
the contribution of ascorbate. Baseline plasma FRAP and FRAPAO were 445
+/- 35 and 363 +/- 35 microM trolox equivalents, respectively. Apple
consumption caused an acute, transient increase in both plasma FRAP and
FRAPAO, with increases after 1 h of 54.6 +/- 8.7 and 61.3 = 17.2 microM
trolox equivalents, respectively. This increase in plasma antioxidant
capacity was paralleled by a large increase in plasma urate, a metabolic
antioxidant, from 271 +/- 39 microM at baseline to 367 +/- 43 microM
after 1 h. In contrast, FRAP and FRAPAO time-dependently decreased after
bagel consumption, together with urate. Consumption of fructose mimicked
the effects of apples with respect to increased FRAP, FRAPAO, and urate,
but not ascorbate. Taken together, our data show that the increase in
plasma antioxidant capacity in humans after apple consumption is due
mainly to the well-known metabolic effect of fructose on urate, not
apple-derived antioxidant flavonoids.

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