Update: The same researchers who’ve found that onions and garlic can increase the bioavailability of zinc in plants have found that the following foods also help: beta-carotene rich vegetables (such as carrots). lime, ginger, red and black pepper.
Yes, a plant-based diet is great for fighting cancer because plants contain all sorts of anti-cancer compounds, but heed the traps: Too much copper and too little zinc, often a result of plant-only diets, can fuel cancer—as well as make you tired.
photo of Venus fly trap courtesy of Beatrice Murch
Copper and Angiogenesis
When a tumor grows to about the size of a pinhead, it starts to generate blood vessels, which bring it nourishment, allowing it to grow bigger and spread. That’s the process of angiogenesis. Over the past decade, researchers have found that copper plays a key role in angiogenesis and that many patients with advanced cancers have high levels of copper in their blood and tissues.
Starting with the work of Dr. George Brewer at the University of Michigan and most recently, with studies at Cornell’s medical school, scientists have also found that lowering copper levels with a drug called Tetrathiomolybdate (TM) can help slow metastasis and keep tumors dormant. The most recent study—which followed 40 patients with breast cancer who had high risk of relapse—found a significant reduction in an important driver of metastasis only in patients who were depleted of copper. The authors are continuing to follow many of the women and calling for more extensive studies in humans.
“While there are many important components of angiogenesis, copper is emerging as essential through experiments that demonstrate decreased endothelial cell proliferation, blood vessel formation, and tumor growth with copper depletion,” the authors said. (Endothelial cells line blood vessels and control the passage of materials into and out of the bloodstream.)
Copper and Your Lifestyle
So what are the potential sources of copper in your body? Copper water pipes, copper cookware, copper IUDs, along with some multi-vitamins, birth control pills and dental amalgams could all be culprits. So could your diet.
The foods highest in copper include organ meats such as liver and kidney and shellfish–especially oysters, lobster, squid and Alaskan king crab. (Shrimp and scallops are not as high.)
The problem for us plantaholics, however, is that many otherwise healthy plant foods are also high in copper.
Many nuts, seeds and beans as well as some vegetables, fruits, grains, herbs and spices are high in copper. So is chocolate—the darker it is, the higher in copper, an industry spokesperson told me. And organic agriculture sometimes uses fertilizers that can increase copper.
As cliche as it may sound, the devil is in the details and moderation is key. Cashews and sesame seeds are particularly high in copper. Green avocados from Florida are higher in copper than the black and bumpy-skinned Hass avocados from California. And rooibos tea (which is not truly tea but from a bush in South Africa) contains copper while real green tea is clean.
Short of studying and measuring everything we put in our mouths, is there a solution for those of us emphasizing plant-based diets? Yes. Get more zinc.
The US and Canada recommend around 1 mg/copper/ day and at least 8 mg/zinc/day for healthy adult women, 11 for healthy adult men. Vegetarians and the elderly may need twice as much zinc, they say, with the maximum set at 40 mg/day. But why is that the upper limit? The sole reason seems to be that high intakes of zinc deplete copper.
Large quantities of zinc (more than 50/mg/day of supplements) over a period of weeks can prevent your body from absorbing copper. Zinc also boosts your immune system, helps repair DNA and acts as an anti-oxidant and anti-carcinogen. And other than depleting copper, zinc appears to be perfectly safe in that 50/mg/day range. (Apparently if you have too much, you excrete it.)
How to Get more Zinc and Less Copper
Phytic acid, common in nuts, seeds, grains and beans, has been called the dilemma in human nutrition. On the good side, it has anti-cancer properties. On the bad side, it binds amino acids and certain minerals, including zinc, making them unavailable to your body. (Unfortunately, for some reason that scientists do not completely understand, phytic acid doesn’t prevent you from absorbing the copper in those foods.)
● Soaking and sprouting these foods, however, helps degrades the phytic acid and make zinc more bioavailable. While it’s difficult to go to that extreme every time you cook, get the most out of your efforts by soaking and sprouting plant foods that contain lots of zinc.
Pumpkin seeds are especially rich in zinc (and you can actually purchase pumpkin seeds that are already sprouted.) Lentils, chickpeas and quinoa are also good zinc sources.
● Fermentation also degrades phytic acid, so choose fermented soy (tempeh, natto, miso) over non-fermented (tofu, soymilk, edamame).
● Choose fresh plants over dried ones (such as sun-dried tomatoes, dried mushrooms and seaweeds). Dried plants are higher in copper.
● And avoid indulging in dishes that use large amounts of beans, whole grains, nuts or seeds. Fake cheeses and fake ice cream made of cashews may be scrumptious, but they’re laden with copper. If you’re going to eat a fake cracker made with nuts and seeds, have just a little bit. Health guru Dr. Andrew Weil suggests limiting nuts to a handful per day.
2/ Eat food sources of zinc several hours away from foods containing phytic acid.
Phytic acid in one food can bind the zinc in another. if you’re having oat bran for breakfast, for example, then have your zinc-rich animal serving at dinner time—without nuts, seeds, beans or grains.
3/ Eat onions, shallots, garlic, capers, dill and other leafy greens all the time. Onions and garlic enhance absorption of zinc; quercetin in shallots, red onions, capers and dill helps bind copper and increase zinc absorption; kaempferol in dill and capers helps quercetin work.
4/ Avoid foods and supplements that might deplete zinc, including alcohol, sugar and processed carbs, dairy products to some degree, and iron and calcium supplements.
5/ Talk with your doctor about medications that might suppress zinc absorption—prolonged use of diuretics, for example, or anticonvulsants. Certain antibiotics and bisphosphonates should not be consumed at the same time as zinc.
6/ Talk with your doctor about taking a zinc supplement. Certain blood tests can indicate whether you’re high in copper. While research shows that 50/mg of supplemental zinc a day can help deplete copper, zinc supplements of more than 100/mg a day for a prolonged period may actually promote some cancers.
If you decide to include a zinc supplement in your anti-cancer diet, make sure you take it several hours away from those zinc-binding nuts, seeds, grains and beans.
7/ For those who don’t have cancer, you might want to include a little high quality (organic and pastured, also called grass fed), properly cooked (at low, not high temperatures) animal food in your diet occasionally. The zinc from animals, in contrast to the zinc from most plants, is easy for your body to absorb.
Here’s a list of the approximate zinc content in 100 grams of some low copper animal foods:
● Beef, lamb, veal (dark meat, not white)—6 to 7 mg zinc
● Turkey dark meat—4+ mg zinc
● Veal white meat—3.5 mg zinc
● Chicken dark meat—2.5 mg zinc
● Turkey and chicken white meat—1+ mg zinc
● Canned sockeye or pink salmon—1 mg zinc (100 grams is ½ of a small can.)
My top choices: turkey dark meat, every so often. Turkey has more selenium as well as zinc than chicken does. I also favor canned pink salmon for its omega 3s. And occasionally, very occasionally, I’ll splurge on some organic, grass-fed, grass-finished red meat.
How should you cook those turkey thighs and legs? Remove the skin along with the thin layer of fat just below it. Emphasize low temperature methods, especially boiling, steaming, poaching, stewing and braising (without browning beforehand). Avoid high temperatures, including grilling, bar-b-cuing, deep and pan frying, and roasting at temperatures so high that water is removed. (That’s why those roasted birds from the grocery store shrink. Avoid them, by all means.)
If you do have cancer, however, animal foods are a problem. They contain lots of the amino acid methionine--the only amino acid that triggers free radicals. Many cancers are methionine-dependent, says Australian researcher Dr. Paul Cavuoto. “ If I had cancer, I would certainly seek to restrict methionine in my diet, probably to 1 gram a day (so long as I don’t become deficient in key vitamins and nutrients),” he says.
Half a small chicken breast has almost 800 milligrams.
Read more on low protein and anti-cancer diets here.