Does Rye Bread Protect Against Cancer?

Transcript: Does Rye Bread Protect Against Cancer?
Previously I’ve explored the beneficial effects of flaxseeds on prostate cancer as well as breast cancer prevention and survival, thought to be because of the lignans in flaxseeds, which are anticancer plant compounds found in red wine, whole grains, greens (cruciferous vegetables), but especially sesame seeds and flaxseeds, the most concentrated source on Earth. But this is per unit weight. People eat a lot more grains than seeds.

And of the grains people eat, the highest concentration of lignans is found in rye. So, can rye intake decrease the risk of breast cancer? Theoretically? Yes, but unlike flaxseeds, it’s never been put to the test.

If you measure the levels of lignans in the bloodstream of women living in a region where they eat lots of rye, the odds of breast cancer seem to be cut in half for women with the highest levels, but lignans are also found in tea and berries, and so, they couldn’t be sure where the protection was coming from. So, researchers decided to measure alkylresorcinol metabolites, a class of phytonutrients relatively unique to whole grains. They collected urine from women with breast cancer and women without, and the breast cancer survivors had significantly lower levels compared to women without breast cancer, be they omnivores or vegetarians. This suggests that women at risk of breast cancer consume significantly lower amounts of whole grains like rye.

But if you follow older women in their 50s through 60s, the intake of whole grain products was not associated with risk of breast cancer. A similar result was found for older men; whole grain consumption in one’s 50s and 60s did not seem to be linked to prostate cancer risk. Is it just too late at that point?

Well, we know from data on dairy that diet in our early life may be important in the development of prostate cancer, particularly around puberty when the prostate grows and matures. And so, if you go back and look at what men were drinking in adolescence, daily milk consumption appeared to triple their risk of advanced prostate cancer later in life. And so, researchers looked at daily rye bread consumption during adolescence and indeed those who consumed rye bread daily as kids may have cut their odds of advanced prostate cancer in half. This is consistent with immigrant studies suggesting that the first two decades of life may be most important for setting the pattern for cancer development in later life.

Certainly important for how we should feed our kids, but if we’re already middle-aged, is it too late to change course? To answer this question, researchers in Sweden put it to the test. How about we take men who already have prostate cancer, split them up into two groups, half get lots of rye bread; the other half lots of high fiber, but low lignan wheat bread and see what happens. There’s been some indirect evidence that rye may be active against prostate cancer, like lower cancer rates in regions with high rye consumption, but it had never been directly investigated until this study.

Biopsies were taken from their tumors before and after three weeks of bread eating, and the number of cancer cells that were dying off were counted. There was no change in the cancer cell clearance of the control bread group, but a 180% increase in the number of cancer cells being killed off in the rye group. A follow-up study lasting 6 weeks, found a 14% decrease in PSA levels, a cancer marker suggesting a shrinkage of the tumor.

Now they note that they used very high rye bread intakes, and it remains to be tested if more normal intake levels would have effects that are of clinical importance. As a good red blooded American, my ignorance of the metric system did not flag 485 grams of rye bread a day as out of the ordinary, but that translates to 15 slices! Rather than eating a loaf a day, the same amount of lignans can be found in a single teaspoon of ground flax seeds.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.