The Impacts of Plant-Based Diets on Breast Cancer and Prostate Cancer

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Why do people who eat more plants get less breast and prostate cancer?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

There appears to be a significant protective effect of a vegetarian diet for heart disease and all cancers combined––particularly for those eating vegan, but that’s for total cancer. What about breast cancer and prostate cancer specifically?

There’s been about a half dozen studies on breast cancer risk and various plant-based dietary patterns, and they all found lower risk, as expected. In some studies, vegetarians had less than half the odds of breast cancer compared to nonvegetarians, suggesting vegetarian diets show a protective role against breast cancer risk. In another study, eating a nonvegetarian diet was one of the important risk factors, nearly tripling the odds of breast cancer. In the California Teachers Study, a more plant-based pattern was associated with a significant reduction in breast cancer risk as well. So, even trending in that direction towards a greater consumption of, for example, fruits and vegetables, is associated with a reduced breast cancer risk––particularly for the hardest to treat tumors, which is interesting, offering a potential avenue for prevention.

Some of the reductions in risk were only statistically significant if you included the weight-loss benefits of plant-based eating and associated lifestyle factors, and other reductions of risk––not statistically significant, regardless. Lower risk but not significant. Lower risk but not significant, meaning like in half of these studies, the lower risk may have just been statistical flukes by chance. Okay, but this, for example, was for vegetarians. Do vegan women do any better?

Vegetarian diets seem to offer protection from cancers of the gastrointestinal tract, whereas vegan diets seem to confer lower risk for all cancers put together, and female-specific cancers, in particular––which included breast cancer, but also included cervical, endometrial, and ovarian cancer. After a few more years, they were able to tease out the breast cancer data, and vegans showed consistently lower risk estimates, but not statistically significantly so.

One study in India even suggested that vegetarians who eat eggs have lower risk than vegetarians who don’t. But, put all the studies on egg intake and breast cancer together, and eating like one egg a day—five or more eggs a week—appears to increase breast cancer risk compared to not eating any eggs at all.

An increase of five eggs a week was also associated with a 47 percent increase in fatal prostate cancer. In general, if you look at the effect of plant- and animal-based foods on prostate cancer risk, most studies showed that plant-based foods are associated with either decreased or neutral risk of prostate cancer, whereas animal-based foods, particularly dairy products, are associated with either increased or neutral risk. The dairy and eggs may be why all three studies on prostate cancer in vegans found decreased risk, but half of the vegetarian studies showed no change.

It’s not just about avoiding meat, though. Vegetables and beans specifically were also associated with lower risk, and the same with breast cancer. High intakes of vegetables and pulses, like beans, lentils, and chickpeas, were associated with protection against breast cancer. We’re talking about half the odds of breast cancer eating four or more vegetable dishes a day, or a daily serving of beans or lentils, regardless of whether you eat meat. Note this was one of the studies that only showed a non-statistically significant drop in risk among vegetarians. So, it may be better to be a meat-eater who eats lots of greens and beans, compared to a vegetarian who instead eats lots of junk.

Now, diet recommendations should go beyond just pushing a specific array of foods, and really just promote the overall benefits of eating more whole plant foods in general. But what happens if you do just push more veggies? You don’t know, until you put it to the test: Effect of a Behavioral Intervention to Increase Vegetable Consumption on Cancer Progression Among Men With Early-Stage Prostate Cancer. Oh, that’s exciting, trying increased vegetable intake to not just prevent but treat cancer. Men with biopsy-proven prostate cancer were randomized to an encouragement to eat seven or more servings of vegetables a day. Nice! And the control group was just given some generic dietary info.

And…among men with early-stage prostate cancer under active surveillance, a behavioral intervention that increased vegetable consumption did not significantly reduce the risk of prostate cancer progression. Bummer. But wait a second. The trial wasn’t testing increased vegetable consumption, but the effect of advice to eat more vegetables. Did they actually do it? The behavioral intervention in this study produced robust, sustained increases in vegetable intake for two years, the researchers wrote. But alas, it still didn’t work. At the end of those two years, they were eating two more servings. Wait, just two, not seven? And so, the difference between the vegetable group and the control group was less than two servings. They were also supposed to get at least two servings of tomatoes a day, and two servings of broccoli-type cruciferous vegetables every day; yet, they ended up only eating about an ounce of cruciferous, and less than a tenth of a serving of tomatoes. So, with so little dietary change, it’s no wonder there was so little change in the cancer.

Though it’s possible you also have to cut down on animal foods. In this three-month study for men who had their prostate cancer come back after surgery and radiation, they were able to boost plant foods, restrict animal foods, actually eat some more tomatoes. And the average PSA doubling time (meaning how fast the tumor was growing) slowed from about 22 months to 59 months; so, doubling in less than two years to then taking nearly five years. All just from a three-month dietary intervention, whereas the control group didn’t change. Now, slowing down a tumor is nice, but how about reversing its growth or shrinking it down?

Are strict vegetarians protected against prostate cancer? Yes, those eating strictly plant-based diets have only a fraction of the risk of getting it in the first place, but that’s not the half of it. Yes, the Ornish study. I’ve talked about this before, notable in my How Not to Die from Cancer video. Randomize men with prostate cancer to a diet packed with fruits, vegetables, whole grains, and beans. Tumors on average appeared to shrink, as noted by PSA trending down, while the control group’s cancer continued to grow. Drip some blood from the plant-based group on some prostate cancer growing in a petri dish, and the plant-based blood suppressed the cancer growth almost eight times better. And the more they stuck to their diet, the more their bloodstream suppressed the cancer growth.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

There appears to be a significant protective effect of a vegetarian diet for heart disease and all cancers combined––particularly for those eating vegan, but that’s for total cancer. What about breast cancer and prostate cancer specifically?

There’s been about a half dozen studies on breast cancer risk and various plant-based dietary patterns, and they all found lower risk, as expected. In some studies, vegetarians had less than half the odds of breast cancer compared to nonvegetarians, suggesting vegetarian diets show a protective role against breast cancer risk. In another study, eating a nonvegetarian diet was one of the important risk factors, nearly tripling the odds of breast cancer. In the California Teachers Study, a more plant-based pattern was associated with a significant reduction in breast cancer risk as well. So, even trending in that direction towards a greater consumption of, for example, fruits and vegetables, is associated with a reduced breast cancer risk––particularly for the hardest to treat tumors, which is interesting, offering a potential avenue for prevention.

Some of the reductions in risk were only statistically significant if you included the weight-loss benefits of plant-based eating and associated lifestyle factors, and other reductions of risk––not statistically significant, regardless. Lower risk but not significant. Lower risk but not significant, meaning like in half of these studies, the lower risk may have just been statistical flukes by chance. Okay, but this, for example, was for vegetarians. Do vegan women do any better?

Vegetarian diets seem to offer protection from cancers of the gastrointestinal tract, whereas vegan diets seem to confer lower risk for all cancers put together, and female-specific cancers, in particular––which included breast cancer, but also included cervical, endometrial, and ovarian cancer. After a few more years, they were able to tease out the breast cancer data, and vegans showed consistently lower risk estimates, but not statistically significantly so.

One study in India even suggested that vegetarians who eat eggs have lower risk than vegetarians who don’t. But, put all the studies on egg intake and breast cancer together, and eating like one egg a day—five or more eggs a week—appears to increase breast cancer risk compared to not eating any eggs at all.

An increase of five eggs a week was also associated with a 47 percent increase in fatal prostate cancer. In general, if you look at the effect of plant- and animal-based foods on prostate cancer risk, most studies showed that plant-based foods are associated with either decreased or neutral risk of prostate cancer, whereas animal-based foods, particularly dairy products, are associated with either increased or neutral risk. The dairy and eggs may be why all three studies on prostate cancer in vegans found decreased risk, but half of the vegetarian studies showed no change.

It’s not just about avoiding meat, though. Vegetables and beans specifically were also associated with lower risk, and the same with breast cancer. High intakes of vegetables and pulses, like beans, lentils, and chickpeas, were associated with protection against breast cancer. We’re talking about half the odds of breast cancer eating four or more vegetable dishes a day, or a daily serving of beans or lentils, regardless of whether you eat meat. Note this was one of the studies that only showed a non-statistically significant drop in risk among vegetarians. So, it may be better to be a meat-eater who eats lots of greens and beans, compared to a vegetarian who instead eats lots of junk.

Now, diet recommendations should go beyond just pushing a specific array of foods, and really just promote the overall benefits of eating more whole plant foods in general. But what happens if you do just push more veggies? You don’t know, until you put it to the test: Effect of a Behavioral Intervention to Increase Vegetable Consumption on Cancer Progression Among Men With Early-Stage Prostate Cancer. Oh, that’s exciting, trying increased vegetable intake to not just prevent but treat cancer. Men with biopsy-proven prostate cancer were randomized to an encouragement to eat seven or more servings of vegetables a day. Nice! And the control group was just given some generic dietary info.

And…among men with early-stage prostate cancer under active surveillance, a behavioral intervention that increased vegetable consumption did not significantly reduce the risk of prostate cancer progression. Bummer. But wait a second. The trial wasn’t testing increased vegetable consumption, but the effect of advice to eat more vegetables. Did they actually do it? The behavioral intervention in this study produced robust, sustained increases in vegetable intake for two years, the researchers wrote. But alas, it still didn’t work. At the end of those two years, they were eating two more servings. Wait, just two, not seven? And so, the difference between the vegetable group and the control group was less than two servings. They were also supposed to get at least two servings of tomatoes a day, and two servings of broccoli-type cruciferous vegetables every day; yet, they ended up only eating about an ounce of cruciferous, and less than a tenth of a serving of tomatoes. So, with so little dietary change, it’s no wonder there was so little change in the cancer.

Though it’s possible you also have to cut down on animal foods. In this three-month study for men who had their prostate cancer come back after surgery and radiation, they were able to boost plant foods, restrict animal foods, actually eat some more tomatoes. And the average PSA doubling time (meaning how fast the tumor was growing) slowed from about 22 months to 59 months; so, doubling in less than two years to then taking nearly five years. All just from a three-month dietary intervention, whereas the control group didn’t change. Now, slowing down a tumor is nice, but how about reversing its growth or shrinking it down?

Are strict vegetarians protected against prostate cancer? Yes, those eating strictly plant-based diets have only a fraction of the risk of getting it in the first place, but that’s not the half of it. Yes, the Ornish study. I’ve talked about this before, notable in my How Not to Die from Cancer video. Randomize men with prostate cancer to a diet packed with fruits, vegetables, whole grains, and beans. Tumors on average appeared to shrink, as noted by PSA trending down, while the control group’s cancer continued to grow. Drip some blood from the plant-based group on some prostate cancer growing in a petri dish, and the plant-based blood suppressed the cancer growth almost eight times better. And the more they stuck to their diet, the more their bloodstream suppressed the cancer growth.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

Check out the How Not to Die from Cancer video I mentioned. 

I’ve produced scores of videos on cancer, and here are some of my more recent ones:

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