The Catechin’s Out of the Bag
This week I’m talking about cancer-fighting foods. The subject is slightly controversial, because much of the evidence for the protective benefits of certain foods is more or less circumstantial. Epidemiological evidence, for example, looks at large groups of people and then attempts to find associations between behaviors and health outcomes. For example, research has shown that Asian women who drink up to six cups of green tea a day are much less likely to develop breast cancer than women who don’t drink green tea.
But scientists are uncomfortable with indirect evidence. They prefer controlled clinical trials, in which some people receive a food, and some don’t, and no one knows who is in which group. These randomized, placebo-controlled, double-blind trials are the gold standard. They’re also extremely expensive, time-consuming, and difficult to conduct.
Much of the evidence for the benefits of certain foods or food components is based on epidemiological studies. Scientists are uncomfortable making assertions based on these types of studies, because they do not prove causality. Rather, they can only make assumptions about apparent associations. Nevertheless, I’m willing to go out on a limb and say that we can draw some useful conclusions from the available evidence about certain foods and their impact on cancer risk.
Let’s take green tea, for instance. It contains chemicals called “catechins.” Research has shown that these chemicals affect cellular processes related to the suppression of cancer. And then there’s the epidemiological evidence. As I mentioned, Asian women who drink green tea tend to get breast cancer less often than women who don’t consume tea. This suggests that something about green tea helps prevent breast cancer. All the evidence points to a catechin in green tea called EGCG. Although there’s some EGCG in black tea, this beneficial compound is more abundant in green or white teas, so drink green tea to get the most cancer-fighting benefits.
Shankar S1, Ganapathy S, Srivastava RK. Green tea polyphenols: biology and therapeutic implications in cancer. Front Biosci. 2007 Sep 1;12:4881-99.
Thangapazham RL1, Singh AK, Sharma A, Warren J, Gaddipati JP, Maheshwari RK. Green tea polyphenols and its constituent epigallocatechin gallate inhibits proliferation of human breast cancer cells in vitro and in vivo. Cancer Lett. 2007 Jan 8;245(1-2):232-41. Epub 2006 Mar 6. Wu AH1, Yu MC, Tseng CC, Hankin J, Pike MC. Green tea and risk of breast cancer in Asian Americans. Int J Cancer. 2003 Sep 10;106(4):574-9.