Transcript: Can Diet Protect Against Kidney Cancer?
58,000 Americans are diagnosed with kidney cancer every year, and 13,000 die. And the numbers have been going up. Approximately 4% of cases are hereditary, but what about the other 96%? The only accepted risk factor has been tobacco use, but cigarette smoking has been declining.
Nitrosamines are one of the most potent carcinogens in cigarette smoke. So much so there’s a concern that nonsmokers may be inadvertently exposed through so-called thirdhand smoke. See, the risks of tobacco exposure do not end when a cigarette is extinguished. Residual smoke particles can contaminate surfaces. About 80% of these nitrosamines in secondhand cigarette smoke stick to room surfaces and are not removed under normal ventilation conditions. That’s why it’s important to only stay in smoke-free rooms in hotels. The bottom line is that there is no way to safely smoke indoors, even if there’s no one else there. Nitrosamines are considered so toxic that carcinogens of this strength in any other consumer product designed for human consumption would be banned immediately. If that were the case, they’d have to ban meat.
One hot dog has as many nitrosamines and nitrosamides as five cigarettes. And these carcinogens are also found in fresh meat as well: beef, chicken, and pork. So even though smoking rates have dropped, perhaps the rise in kidney cancer over the last few decades may have something to do with meat consumption. But would it just be the processed meats, like bacon, sausage, hot dogs, and cold cuts that have nitrate and nitrite additives, or fresh meat as well? We didn’t know, until now.
The NIH-AARP study is the largest prospective study on diet and health ever, with over 4 million person-years of follow-up—about 500,000 followed for 9 years. In addition to examining nitrate and nitrite intake from processed meat, they also looked at intake from other sources such fresh meat, eggs, and dairy. There are nitrates in vegetables too; should we be worried about those? No. Nitrite from animal sources—not just processed meats—was associated with an increased risk of kidney cancer. Total intake of nitrate and nitrite from processed meat sources was also positively associated with RCC risk. We found no associations with nitrate or nitrite intake from plant sources. But nitrates from processed meat were associated with cancer. That’s when they advertise their bacon or lunch meat as “uncured,” with no nitrites or nitrates added, except for the celery juice they added, which is just a sneaky way to add nitrites. See, they ferment the nitrates in celery to nitrites, then add it to the meat, a practice even the industry admits may be viewed as incorrect at best, or deceptive at worst.
But that same fermentation of nitrates to nitrites can happen thanks to bacteria on our tongue when we eat vegetables. So why are nitrates and nitrites from vegetables on our tongue okay, but nitrates and nitrites from vegetables in meat linked to cancer? Because the actual carcinogens are not nitrites, but nitrosamines and nitrosamides. In our stomach, to turn nitrites into nitros-amines and nitros-amides, we need amines and amides, which are concentrated in animal products. And vitamin C and other antioxidants in plant foods block the formation of these carcinogens in our stomach. That’s why we can safely benefit from the nitrates in vegetables without the cancer risk. In fact, some of the highest nitrate vegetables like arugula, kale, and collards, are associated with decreased risk of kidney cancer. The more plants, it appears, the better.
Plant-based diets and fiber-rich diets are recommended to prevent cancer directly, as well as chronic conditions associated with kidney cancer, such as obesity, high blood pressure, and diabetes, so a plant-based diet may help protect against kidney cancer directly or indirectly. It’s like sodium intake and kidney cancer. Sodium intake increases kidney disease risk, but is that just because it increases blood pressure? No, it appears the salt is associated with increased cancer risk even independently of hypertension. What about plant-based diets? Turns out the protective association remains even in people who aren’t obese, with normal blood pressure. So overall, plant-based and fiber-rich diets appear to do both, decreasing cancer risk both directly and indirectly.
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.
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