Numerous trials have demonstrated the benefits of almonds on the heart. Some years ago researchers at the University of Toronto found that people eating a handful of almonds a day as part of a healthy diet lifestyle lowered their LDL cholesterol by 3 per cent. Several studies later supported this impact on cholesterol levels.
However it is not clear why almonds are so helpful. They are rich in the antioxidant vitamin E, thought to be beneficial for the heart. But the new study shows that the flavonoids found predominantly in the nuts' skin could be at least one of the key factors in cholesterol reduction.
A team from the Antioxidants Research Laboratory at the Jean Mayer Human Nutrition Research Center on Aging in the US extracted almond skin flavonoids and used HPLC tests to identify their content of catechins and flavonols.
Then they assessed the bioactivity of the antioxidants in vitro, testing their capacity to increase the resistance of human LDL to oxidation. The flavonoids increased the lag time to LDL oxidation in a dose-dependent manner, report the researchers in this month's Journal of Nutrition (issue 135, pp1366-1373).
Combining the extract with vitamin E or ascorbic acid extended the lag time considerably more and when these nutrients were tested in hamsters, the bioavailability of catechin, epicatechin, and flavonols was confirmed.
The almond skin flavonoids enhanced the ex vivo resistance of hamster LDL to oxidation by 18 per cent, and the in vitro addition of 5.5 µmol/L vitamin E synergistically extended the lag time of the 60-min sample by 52.5 per cent, they report.
"Almond skin flavonoids possess antioxidant capacity in vitro; they are bioavailable and act in synergy with vitamins C and E to protect LDL against oxidation in hamsters," conclude the researchers.