"The Role of Soy Foods in Prostate Cancer Prevention"
A compilation of 13 observational studies on soy food consumption
and the risk of prostate cancer found that soy foods
appear to be protective.
Observational studies, as opposed to interventional studies—
they observed what people were eating but didn’t intervene
and try to change their diets.
So, they observed that men who ate more soy foods
had lower rates of prostate cancer,
but the problem with observation studies is that
there could be confounding factors.
Maybe people who choose to eat soy may also make other
healthy lifestyle decisions, like eating more fruits and vegetables,
and maybe that’s actually why they have less cancer.
Most of the studies tried to control for these other lifestyle factors,
but you can’t control for everything.
Most of the studies were done in Asia;
so, maybe tofu consumption is just a sign
of eating more of a traditional diet.
Maybe the reason non-tofu consumers got more cancer
is that they had abandoned their traditional diet?
If only there was a Western population that ate a lot
of soy that we could look at it.
There is: Seventh Day Adventists.
In the 70s, more than 12,000 Adventist men were asked
about their use of soy milk,
and then, they were followed for up to 16 years
to see who got cancer and who did not.
So, does high soy milk intake reduce prostate cancer incidence?
Frequent consumption of soy milk was associated with
a whopping 70 per cent reduction of the risk of prostate cancer.
Similarly, in a multiethnic study that involved a number of groups,
soy intake appeared protective in Latinos too.
Prostate cells carry beta type estrogen receptors,
which appear to act as tumor suppressors,
kind of a gatekeeper, inhibiting invasion, proliferation,
and preventing the prostate cells from turning cancerous in the first place.
And, those are the receptors targeted by the phytoestrogens in soy,
like genistein, which inhibits prostate cancer cell invasion
and spread in a petri dish at the kinds of levels
one might get consuming soy foods.
The prevention of metastases is critical,
as death from prostate cancer isn’t caused by the original tumor,
but its spread throughout the body,
which explains recommendations for men with prostate cancer
to consume soy foods as well.
Wait a second.
Do you think the amazing results Dean Ornish and colleagues got,
apparently reversing the progression of prostate cancer
with a plant based diet and lifestyle program,
was because of the soy?
It wasn’t just a vegan diet, but a vegan diet supplemented
with a daily serving of tofu and a soy protein isolate powder.
There have been studies showing men given soy protein powders
develop less prostate cancer than the control group,
but what was the control group getting?
Milk protein powder.
Those randomized to the milk group got six times more prostate cancer.
But is that from the beneficial effects of soy
or the deleterious effects of the dairy?
Dairy products are not just associated with getting prostate cancer,
but also dying from prostate cancer.
Men diagnosed with prostate cancer who then ate more dairy
tended to die sooner.
And, both low-fat and high-fat dairy consumption were associated
with an increased risk of a fatal outcome.
The best study we have on soy protein powder supplementation
for prostate cancer patients found no significant benefit,
and neither did a series of soy phytoestrogen dietary supplements.
Maybe that’s because they just used isolated soy components
rather than a whole soy food?
Taking the whole food approach may be more efficacious.
It’s hard to do controlled studies with whole foods though;
you can make fake pills,
but how do you give people placebo tofu?
This group of Australian researchers got creative
coming up with a specially manufactured bread containing soy grits
compared to just placebo regular bread
and then gave slices to men diagnosed with prostate cancer
awaiting surgery,
and, in just about 3 weeks time, did see a remarkable difference.
The first study to show a diet incorporating a whole soy food
could favorably affect prostate cancer markers.
But, it’s not like you can go out and buy soy grit bread.
This study was a little more practical.
Twenty men with prostate cancer who were treated
with radiation or surgery, but seemed to be relapsing,
were asked to drink three cups of regular soy milk a day.
Here’s what happened to the PSA levels in each
of the 20 patients before they started the soy milk.
They were all rising, suggesting they had relapsing
or metastatic cancer growing inside of them.
Here’s what happened during the year on soy milk.
The blue lines are the folks where the soy milk
appeared to have a positive effect,
slowing or reversing the rise.
The red lines represent those that got even worse during that period,
and the black lines are those in which there appeared
to be no significant change.
So, of the 20, 6 got better, 2 got worse,
and the remaining 12 remained unchanged.
So, they conclude soy food may help in a subset of patients.
Based on all these studies, the results Ornish got
were probably more than just the soy.
Similarly, the low prostate cancer rates in Asia
are probably more than just the soy,
since the lowest rates are also found in parts of Africa,
and I don’t think they’re eating a lot of tofu in Africa.
Indeed, in a multiethnic study, other types of beans besides soy
also appeared protective for Latinos; and all the groups put together,
when looking at the most aggressive forms of prostate cancer.
And so, the protection associated with plant based diets
may be due to eating a variety of healthy foods.