These results were seen in a petri dish, though, and while such studies may have direct relevance for digestive-tract cancers that come in close contact with these foods, for these foods to be protective against other cancers, the anticancer compounds would have to be absorbed into the bloodstream. And in the case of brain tumors, the anticancer compounds would additionally have to cross the blood-brain barrier. The findings do seem to sync with other studies, though, both among human populations and in other laboratories, that corroborate the cancer-fighting benefits of cruciferous vegetables,64 garlic, and onions.65 Regardless, this study illustrates the dramatic differences between the biological capacities of individual vegetables and families of veggies and underscores the importance of including a variety of vegetables in your diet.
Which Is the Best Cooking Method?
Is it better to eat your vegetables raw or cooked? If you’re thinking raw, you’re right. But if you guessed cooked, you’re also right.66 Confused? Well, a number of nutrients, like vitamin C, are partially destroyed by cooking. For example, steamed broccoli may have about 10 percent less vitamin C than raw broccoli.67 If, however, you prefer cooked broccoli enough to eat seven florets of steamed rather than six florets of raw, then you just more than made up the difference.
Other nutrients, however, actually become more absorbable after cooking. For example, you end up with more than six times the vitamin A in your bloodstream from cooked carrots compared to raw ones.68 A study of long-term raw foodists found surprisingly low blood levels of the red antioxidant pigment lycopene.69 It’s not what you eat but what you absorb, and cooked tomatoes appear able to better boost your lycopene levels.70 Steaming may also improve the bile acid-binding capacity of vegetables,71 which may help lower breast cancer risk.72
Raw-food diets automatically eliminate most red- and yellow-light foods, which is not only an improvement over the standard American diet but also over many plant-based diets. There is no evidence to suggest, however, that eating raw foods largely or exclusively is healthier than eating a combination of cooked and raw whole plant foods.
Some cooking methods, though, are preferable to others. Deep-fried foods, whether of plant origin (like french fries) or from animals (like fried chicken), have been associated with higher cancer risk.73 Deep-frying leads to the production of dangerous heterocyclic amines in meat (as detailed in chapter 11) and to acrylamide in deep-fried plant foods. The excess lifetime cancer risk attributable to the consumption of french fries in young children, for example, may be as high as one or two in ten thousand—meaning about one in ten thousand boys and girls eating french fries may develop cancer that would have otherwise not occurred had they not eaten french fries. The researchers urge deep-fryer cooking times and temperatures be set as low as possible “while still maintaining a tasty quality.”74 (They wouldn’t want to reduce cancer so much that the deep-fried foods wouldn’t be as tasty!) Blanching potatoes first can reduce acrylamide formation, but crisp companies argue that this might have a negative impact on the “nutritional properties of the fried product,” because it would leach away some of the vitamin C.75 But if you’re relying on crisps to get your vitamin C, acrylamide is probably the least of your worries.
What is the best way to cook vegetables to preserve nutrition? I am often asked that question, and it’s difficult to answer, as it varies for different vegetables. What we would need is a study that measures a variety of different cooking methods with a variety of different vegetables. Thankfully, we got exactly that in 2009. A Spanish research team pulled out all the stops, performing more than three hundred separate experiments with twenty vegetables and six cooking methods, all while considering three different measures of antioxidant activity. They tested baking, boiling, frying, griddling (cooking in a thick frying pan with no oil), microwaving, and pressure-cooking.76
Let’s start with the worst methods in terms of antioxidant loss: boiling and pressure-cooking. When you use these wet-cooking methods, some of the nutrition is lost into the cooking water, but less than I would have thought. For instance, the researchers found that boiling removes an average of 14 percent of the vegetables’ antioxidant capacity. So, if you like your corn on the cob boiled, you could just add an extra quarter ear to the pot. (Six quarters boiled may have all the antioxidant power of five quarters raw, baked, or microwaved.77) Of the six cooking methods studied, griddling and microwaving were actually the gentlest. Nuking your veggies appears to preserve, on average, more than 95 percent of antioxidant capacity.78
Those are averages across twenty vegetables, however. Some vegetables are more resistant, and antioxidant power actually increases with cooking in some veggies. Which do you think was the most vulnerable vegetable—that is, the one probably best eaten raw? If you guessed peppers, you’re right. They’ve been shown to lose up to 70 percent of their antioxidant capacity when baked in an oven. I’m going to continue to roast my peppers because of how much I love the taste, but I realize I’m getting less nutritional bang for my buck. (No worries, though, because I can just add an extra sprinkle of oregano to my roasted red pepper pasta sauce.)
On the other hand, three vegetables hardly seem to be affected at all by cooking: artichokes, beetroot, and onions. You can even boil them, and they’ll still retain 97.5 percent of their antioxidant power.
Finally, there are two vegetables that may actually become healthier through cooking: the humble carrot and the celery stalk. No matter how you prepare them—even by boiling—carrots and celery appear to gain in antioxidant power. Green beans get an honorable mention, because they increase in antioxidant power when cooked by all methods except boiling or pressure-cooking. Microwaved green beans, for example, have more antioxidants than raw. So go ahead and make a nice vegetable soup and boost the ingredients’ antioxidant content at the same time.
How to Make Your Own Fruit and Vegetable Wash
Buying organic foods reduces your exposure to pesticides, but it doesn’t eliminate them entirely. Pesticide residues have been detected in 11 percent of organic crop samples due to accidental or fraudulent use, cross-contamination from neighboring nonorganic fields, or the lingering presence of persistent pollutants like DDT in the soil.79
There are many commercial fruit and vegetable wash products that purport to improve the removal of pesticides, but a variety have been tested and appear to be a complete waste of money.80 For example, Procter & Gamble had a product that claimed it was “proven to be 98% more effective than water in removing pesticides.” When it was put to the test, though, it did no better than plain tap water.81 Rinsing produce under running water generally removes less than half of the pesticide residue.82 A fingernail-polish-remover acetone bath has been found to be more effective at removing pesticides,83 but of course I’m not advocating dunking your fruits and veggies in that! The goal is to make your tomato less toxic.
One effective method is to use a 5 percent acetic-acid bath—in other words, plain white vinegar, which has been found to remove the bulk of certain pesticide residues.84 But 5 percent is full strength, and it would get expensive buying gallons of white vinegar just to wash your fruits and veggies. Unfortunately, a diluted white-vinegar bath only seems marginally more effective than tap water.85
Thankfully, there is a solution that is both cheap and effective: salt water. A 10 percent saltwater rinse has been found to work as well as full-strength vinegar.86 To make your own pesticide-reducing bath, add one part salt to nine parts water. Just make sure to rinse off all the salt before eating.
Is Buying Organic Worth It?
Stroll down the produce aisle of your supermarket. You’ll see lots of foods labeled “organic,” but what does that really mean?
According to the USDA, organic farming practices preserve the environment and avoid most synthetic materials, including pesticides and antibiotics. Among other requirements, organic farmers must receive annual on-site inspections, use only USDA-approved materials, and not use genetically modified crops. In
order to be counted in the $35 billion (£22 billion) U.S. organic retail market, products receive a USDA organic stamp.87
The fact is that being organic doesn’t mean a food is healthy. The organic food industry didn’t become so lucrative by selling carrots. For instance, you can now buy pesticide-free crisps and organic jelly beans.88 There are even organic Oreo cookies. Junk food is still junk food, even if it was produced organically. The organic label cannot turn red lights green.
Many are surprised to learn (I know I was!) that a review of hundreds of studies found that organic produce does not seem to have significantly more vitamins and minerals. Organic fruits and vegetables do, however, appear to have more nontraditional nutrients like polyphenol antioxidants,89 thought to be because conventionally grown plants given high-dose synthetic nitrogen fertilizers may divert more resources to growth rather than defense.90 This may be why, as we learned in chapter 4, organic berries appear to suppress cancer growth better than conventional berries in vitro.
Based on its elevated antioxidant levels, organic produce may be considered 20–40 percent healthier, the equivalent of adding one or two servings’ worth to a five-a-day regimen. But organic produce may be 40 percent more expensive, so for the same money, you could just buy the extra servings’ worth of conventional produce. From a purely nutrients-per-pound standpoint, it’s not clear that organic foods are any better.91 But people don’t just buy organic foods because they’re healthier—what about safety?
Conventional produce appears to have twice the levels of cadmium, one of the three toxic heavy metals in the food supply, along with mercury and lead.92 The cadmium is thought to come from the phosphate fertilizers that are added to conventional crops.93 The greatest concern most people have about conventionally grown produce, though, is the pesticide residues.
People not only tend to overestimate the nutritional benefit of organic food, they also overestimate the risks of pesticides.94 For example, surveys have found that many consumers erroneously believe that just as many people die from pesticide residues on conventional food as they do from car accidents,95 or that eating nonorganic produce is almost as bad as smoking a daily pack of cigarettes.96 This kind of thinking is dangerous, as it could lead to a decrease in overall fruit and vegetable consumption.
If just half of the U.S. population were to increase fruit and vegetable consumption by a single serving per day, an estimated twenty thousand cancer cases might be avoided each year. This estimate was calculated using conventional produce, so the additional pesticide burden from all that extra produce might be expected to cause ten new cancer cases. On balance, the study suggested, if half of Americans ate one more serving of produce per day, we’d prevent 19,990 people from becoming cancer patients every year. Sounds good to me!
Unfortunately, this paper was written by scientists-for-hire paid by conventional produce growers, so they had an incentive to exaggerate the benefits and downplay the risks.97 Nevertheless, I think the bottom line is sound. You receive tremendous benefit from eating conventional fruits and vegetables that far outweighs whatever little bump in risk you may get from the pesticides.98 But why accept any risk at all when you can choose organic? My own family buys organic whenever we can, but we never let concern about pesticides stop us from stuffing our faces with as many fruits and vegetables as possible.
At least half your plate should be filled with vegetables. Here’s a simple rule: Include vegetables in everything, and the more the better. Bean burritos are better than carnitas, but better still is a bean burrito with lots of veggies wrapped inside. Instead of spaghetti with marinara sauce, make it spaghetti with marinara sauce . . . and loads of veggies. Marinara is certainly better than Alfredo, but it’s even better still to go the extra veggie mile and heap on your favorite vegetables.
Flaxseeds
Dr. Greger’s Favorite Flaxseeds
Golden or brown
Serving Size:
1 tablespoon ground
Daily Recommendation:
1 serving per day
I have talked about the wonders of flaxseeds in a few of this book’s earlier chapters, including those on high blood pressure (chapter 7), breast cancer (chapter 11), and prostate cancer (chapter 13). Remember how flaxseeds apparently offer “miraculous defense against some critical maladies”?
Okay, you’re convinced. But just where do you get flaxseeds, and how do you best use them?
You can buy flaxseeds in bulk at natural foods stores for just a few pounds. They come in nature’s finest packaging: a hard natural hull that keeps them fresh. However, Mother Nature packs them a little too well. If you eat flaxseeds whole, they’re likely to pass right through you without releasing any of their nutrients. So, for best results, first grind up the seeds with a blender or coffee or spice grinder, or buy them preground or “milled.” (The other option is to chew them really well.) Thanks to their antioxidant content, ground flaxseeds should last at least four months at room temperature.1
Ground flax is a light, nutty powder that can be sprinkled on oatmeal, salads, soups—frankly, just about anything you’re eating. You can even bake with flax without damaging the lignans2 or omega-3 fatty acids3 (unlike flaxseed oil). During medical school, I used to make a few dozen flaxseed muffins at a time and put them in the freezer. Then I’d pop one in the microwave every morning before I ran out the door and get my daily flax fix while eating breakfast surreptitiously on the Tube.
Are Fruit-and-Nut Bars Fattening?
There are a number of energy bars on the market containing only green-light ingredients, such as dried fruits, seeds, and nuts. People love them because they’re so easy to throw into a briefcase, backpack, or bag and eat as a convenient snack on the go.
Dried fruits, seeds, and nuts are all nutrient-dense foods, but they’re also calorie dense. Might concentrating so many calories into such a small energy bar contribute to weight gain? To find out, Yale University researchers split about one hundred overweight men and women into two groups. All the participants ate their normal diet, but half were told to add two fruit-and-nut bars daily. After two months, despite the extra 340 calories a day from the bars, the fruit-and-nut bar group did not gain any weight.4
Dried fruits and nuts appear to be so satiating that people feel full and unintentionally offset the calories elsewhere throughout the day. Studies on apple rings,5 figs,6 prunes,7 and raisins8 have found similar results. In the apple study, postmenopausal women who added two apples’ worth of apple rings to their daily diet for six months not only didn’t gain weight but experienced a whopping 24 percent drop in their LDL (“bad”) cholesterol.9 (That’s nearly the effect you can get with some statin drugs!) In general, the 7 percent of Americans who average a tablespoon or more of dried fruit per day tend to be less overweight and less obese, and they have slimmer waistlines and less abdominal obesity than Americans who don’t eat as much dried fruit.10
Of course, when shopping for energy bars, it’s imperative that you read their labels, as many brands have added sugars. Or you can just save yourself some money and choose good old-fashioned trail mix. Better yet, how about eating a piece of fresh fruit? Still, if the choice is between an energy bar and a chocolate bar as an afternoon snack, the choice is clear.
Other Ways to Eat Flaxseeds
When you’re not sprinkling ground flax on your cereal, salads, or soups or baking it into your muffins, there are plenty of other ways to get your daily serving of flaxseeds. There are a lot of convenient flax bars, crackers, and snacks on the market these days, a few of which even have all green-light ingredients.
Honestly, it’s pretty easy to make your own flax crackers. Mix 200 grams of ground flaxseeds with 250 ml of water, add whatever herbs and spices you want, and then spread the dough thinly on a parchment- or silicone-lined baking sheet. Score the dough into thirty-two crackers and bake at 200°C for about twenty minutes. To flavor mine, I use half a teaspoon each of smoked paprika, garlic powder, and onion powder, but you sh
ould play around until you find a (salt-free) spice profile you prefer. When cut into thirty-two pieces, each cracker meets your Daily Dozen serving requirement.
I also use my trusty discount dehydrator to make raw flax crackers. All you do is mix 150 grams of whole flaxseeds with 250 ml of water along with flavorful ingredients like sun-dried tomatoes and basil. After it firms for about an hour and gets a jelly-like consistency, I spread it out thinly and dehydrate away. Give it a try! Dip your flax crackers in hummus or another bean dip for double check marks. Since you’re using whole flaxseeds, though, make sure to chew thoroughly for maximum benefit.
Flaxseeds have a wonderful binding quality that makes them a great ingredient for thick, milkshake-like smoothies. Toss a tablespoon of ground flax into a blender with some frozen berries, unsweetened soya milk, and half a ripe banana or mango or a few dates for sweetness, and you have a delicious drink containing both classes of protective phytoestrogens—lignans in flax and isoflavones in soya. (See chapter 11.) Blend in some cocoa powder for a chocolate milkshake that could help improve your chances of both preventing and surviving breast and prostate cancers.
This same binding quality makes flaxseeds a green-light thickener to replace cornflour. I use flax to make my favorite quickie stir-fry sauce. I start with some bok choy and fresh mushrooms. The water clinging to the bok choy after it’s rinsed, along with the liquid that gets released from the mushrooms while cooking, is enough to flash-steam the veggies in a hot pan without any added oil. Once the bok choy is tender-crisp, I add 250 ml of water mixed with a tablespoon each of tahini, ground flaxseeds, and Asian black-bean garlic sauce, a fermented yellow-light condiment you can find in a jar at most large supermarket. Once the sauce thickens, it’s ready for some fresh ground pepper (and hot sauce, if you’ve got that spicy tooth like I do) and . . . voilà!
How Not to Die Page 43