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From: Chris (cache-mtc-ab09.proxy.aol.com)
Subject:         Re: Soy and IGF-1
Date: January 2, 2007 at 10:31 am PST

In Reply to: Re: Soy and IGF-1 posted by Leslie on November 20, 2006 at 1:02 pm:

Leslie,

"The fact is that many substances, when removed from their whole source are not the same as consuming a whole food. Consider beta-carotene, which in supplement form increased lung cancer, although eating lots of beta carotene in the form of carrots and sweet potatoes has the opposite effect."

The reason in this case appears to be the amount. After the two trials in the 90s found beta-carotene to increase the risk of lung cancer, animal studies showed that the bodyweight-adjusted human equivalent of 6 mg of beta-carotene was protective against lung cancer in ferrets that "smoked" a pack of cigarettes a day, but that 30 mg of beta-carotene ALONE was even WORSE than smoking a pack of cigarettes a day (although the effect was even worse when the two were combined).

When beta-carotene accumulates in the cell to an excess, it is oxidized to "eccentric cleavage products" that upregulate phase I detox enzymes and degrade retinoic acid (the active form of vitamin A), inducing a cellular retinoic acid deficiency, and causing the upregulation of pro-cancer systems that are suppressed by retinoic acid.

It's kind of ironic that its mechanism of toxicity is depleting cells of vitamin A!

In any case, using the same isolated beta-carotene, the animal experiments showed that the equivalent of a human dose of 6 mg, which you could get from vegetables, is protective, while the equivalent of a human dose of 30 mg, which you could probably only get from supplements, is carcinogenic.

Here is an excellent review on the subject:

Russel, Robert M. The Enigma of Beta-Carotene in Carcinogenesis: What
Can Be Learned From Animal Studies, Journal of Nutrition, 2004; 134:
262S-268S.

Chris

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