The researchers used raw kale, but the scant amounts of kale Americans consume are often cooked. Does cooking kale destroy its immune-boosting effects? It turned out that even boiling the veggies nonstop for thirty minutes did not affect antibody production. In fact, the cooked kale appeared to work even better.25
However, this property was discovered in a test-tube study. Even kale aficionados don’t mainline it like heroin, which is presumably the only way intact kale proteins would ever come in direct contact with our blood cells. No clinical studies (that is, studies on real people) on kale have been performed to date. Big Kale, it seems, has yet to muster the research dollars. Currently, we have stronger evidence for the immune benefits of kale’s less pretentious cousin, broccoli.
Broccoli
As I’ve mentioned, your body’s greatest exposure to the outside world is through the lining of your intestines, which may cover more than two thousand square feet,26 which is about the floor area of an average house.27 But the lining is extremely thin—just fifty-millionths of a meter. In other words, the barrier separating your bloodstream from the world is many times thinner than a single sheet of tissue paper. This is because the body needs to absorb nutrients from food: If the gut lining were any thicker, nutrients would have trouble passing through. It’s a good idea for your skin to be waterproof so you don’t start leaking, but the lining of the gut has to allow for the absorption of both fluids and nutrition. With such a fragile layer between your sterile core and the chaos outside, you need to have a good defense mechanism in place to keep out the bad.
This is where the immune system comes in, specifically a special type of white blood cell called intraepithelial lymphocytes. These cells serve two functions: They condition and repair the thin intestinal lining, and they also serve as its first line of gut defense against pathogens.28 These lymphocytes are covered with “Ah receptors” that activate the cells.29 For years, scientists couldn’t find the key that fit into the Ah receptor lock. If we could figure out how to activate these cells, we might be able to boost our immunity.30
It turns out that key is contained in broccoli.
You may have been taught as a kid to eat your veggies, including cruciferous ones like broccoli, kale, cauliflower, cabbage, and brussels sprouts. But your parents probably didn’t tell you why you should eat them. Now we know that this family of vegetables contains compounds necessary for the maintenance of the body’s intestinal defenses. In short, broccoli is able to rally your immune system foot soldiers.31
Why did our immune systems evolve to depend on certain vegetables? Well, when do we need to boost our intestinal defenses? When we eat. The body uses up a lot of energy to maintain its immune system, so why remain on high alert 24-7 when we only eat a few times a day? Why would our bodies specifically use vegetables as the bat signal to assemble the troops? We evolved over millions of years eating mostly weeds—wild plants, including dark-green, leafy vegetables (or, as they were known back then, leaves)—so our bodies may have evolved to equate vegetables with mealtime. Vegetables’ presence in the gut works as a signal to upkeep our immune systems.32 So if we don’t eat plants with each meal, we may be undermining our bodies’ strategy to protect us.
Interestingly, the immune boost provided by cruciferous vegetables like broccoli not only protects us against the pathogens found in food but also against pollutants in the environment. We’re all constantly being exposed to a wide range of toxic substances—from cigarette smoke, car exhaust, furnaces, cooked meat, fish, dairy, and even from mother’s milk33 (as a consequence of what the mother was exposed to). Because some of these pollutants, such as dioxins, exert their toxic effects through the Ah receptor system, cruciferous compounds may block them.34
Other plants may also defend against toxic invaders. Researchers in Japan found that phytonutrients in such plant foods as fruits, vegetables, tea leaves, and beans can block the effects of dioxins in vitro. For instance, the researchers found that having phytonutrient levels in the bloodstream achieved by eating three apples a day or a tablespoon of red onion appeared to cut dioxin toxicity in half. The only catch was that these phytonutrient effects lasted only a few hours, meaning you may have to keep eating healthy foods, meal after meal, if you want to maintain your defenses against pathogens as well as pollutants.35
The ability to block toxins isn’t limited to plant foods, however. There is one animal product that has also been shown to potentially block the cancer-causing effects of dioxins—camel urine.36 So next time your kids don’t want to eat their fruits and veggies, you can just say, “Hey, it’s either the broccoli or camel pee. Your choice.”
Pretty in Pee-nk
Ever noticed that your urine turns a bit pink after you eat beetroot? Though the color looks a little unnatural, it’s a completely harmless and temporary condition called beeturia.37 It’s a vivid reminder of an important fact: When you eat plant foods, many of the pigment phytonutrients that act as antioxidants in your body (such as lycopene and beta-carotene) are absorbed into the bloodstream and bathe your organs, tissues, and cells.
In other words, beetroot pigments find their way into your urine because they are absorbed through the gut and then travel into the bloodstream, where they circulate throughout the body until eventually being filtered out by the kidneys. During this trip through the body, even your blood becomes a bit pinker too.
The same principle causes garlic breath. It isn’t just the residue in your mouth that’s scaring everyone off; it’s also the health-promoting compounds that were absorbed into your bloodstream after you swallowed the garlic, which are then exhaled pungently from your lungs in your breath. Even if you just had a garlic enema, you’d still get garlic breath. For this reason, garlic can potentially be used as an adjunct treatment for critical cases of pneumonia, as it may help clear bacteria on its way out of the lungs.38
Boosting Natural Killer Cell Activity with Berries
For disease prevention, berries of all colors have “emerged as champions,” according to the head of the Bioactive Botanical Research Laboratory.39 The purported anticancer properties of berry compounds have been attributed to their apparent ability to counteract, reduce, and repair damage resulting from oxidative stress and inflammation.40 But it wasn’t known until recently that berries may also boost your levels of natural killer cells.
They may sound sinister, but natural killer cells are a type of white blood cell that’s a vital member of the immune system’s rapid-response team against virus-infected and cancerous cells. They’re called natural killers because they don’t require prior exposure to a disease to be activated, unlike some other parts of the immune system that can only respond effectively after a history of exposure, as in the case of, say, chicken pox.41 After all, you don’t want to wait until your second tumor appears before your immune system starts fighting.
There are about two billion of these elite, special-ops fighters patrolling the bloodstream at any one time, but research suggests that you can bolster their ranks by eating blueberries. In one study, researchers asked athletes to eat about 180 grams of blueberries every day for six weeks to see if the berries could reduce the oxidative stress caused by long-distance running.42 The blueberries succeeded, unsurprisingly, but a more important finding was their effect on natural killer cells. Normally, these cells decrease in number after a bout of prolonged endurance exercise, dropping by half to about one billion. But the athletes consuming blueberries actually doubled their killer cell counts, to more than four billion.
Blueberries can boost the number of natural killer cells, but are there any foods that can boost killer cell activity—that is, how effectively they fight cancer cells? Yes, it seems an aromatic spice called cardamom may be one. Researchers put some lymphoma cells in a petri dish and added natural killer cells, which were able to wipe out about 5 percent of the cancer cells. But after researchers effectively sprinkled on some cardamom, the natural killer cells became supercharged and eradicated even more
cancer cells—up to about ten times more than without cardamom.43 No clinical trials have yet been done to try this out in cancer patients.
In theory, though, cardamom-infused blueberry muffins may increase the number of circulating natural killer cells in the body, as well as boost their cancer-killing instincts.
Preventing the Common Cold with Probiotics?
Babies delivered via cesarean section appear to be at increased risk for various allergic diseases, including allergic runny nose, asthma, and perhaps even food allergies.44 (Allergy symptoms are caused when your immune system overreacts to normally harmless stimuli, such as tree pollen.) Normal delivery leads to the colonization of the baby’s gut with the mother’s vaginal bacteria. C-section babies, on the other hand, are deprived of this natural exposure. The resulting difference in gut flora may affect the way the baby’s immune system develops, accounting for the difference in allergy rates. This explanation is supported by research showing that a disturbance in a mother’s vaginal flora during pregnancy due, for example, to sexually transmitted infections or douching may result in higher asthma risk for the infant.45
These findings raise a broader question about the effects the good bacteria in the gut may have on the immune system. Some studies have shown that supplementing with good bacteria (probiotics) might have immunity-enhancing effects. The first such study demonstrated that white blood cells extracted from subjects on a probiotic regimen for a few weeks demonstrated a significantly enhanced ability to engulf and destroy potential invaders. This effect lasted for at least three weeks after the probiotics were discontinued. Natural killer cell activity against cancer cells in vitro was improved as well.46
Improving cell function in a petri dish is nice, but do these results translate into fewer infections? It took another ten years before a randomized, double-blind, placebo-controlled study was performed. (Considered the gold standard of research, a randomized, double-blind, placebo-controlled study is a trial in which neither the participants nor the researchers know who is receiving an experimental treatment and who is receiving a placebo until the end of the study.) The study showed that people who take probiotic supplements may indeed have significantly fewer colds, fewer sick days, and fewer overall symptoms.47 The evidence to date suggests probiotics may reduce the risk of upper-respiratory-tract infections but is insufficient for recommending that people start popping probiotic pills.48
Unless you’ve suffered a major disruption in gut flora due to a course of antibiotics or an intestinal infection, it may be best to focus on feeding the good bacteria already living in your gut.49 What do your friendly flora eat? Fibre and a certain type of starch concentrated in beans. These substances are called prebiotics. Probiotics are the good bacteria themselves, whereas prebiotics are what your good bacteria eat. So the best way to keep your good bacteria happy and well fed is to eat lots of whole plant foods.
When you eat fresh produce, you can get both pre- and probiotics into your gut. Fruits and veggies are covered with millions of lactic acid bacteria, some of which are the same types used in probiotic supplements. When you make sauerkraut, for example, you don’t need to add a starter culture, because the bacteria are already naturally present on cabbage leaves. Including raw fruits and vegetables in your daily diet may therefore offer the best of both worlds.50
Boosting the Immune System with Exercise
What if there were a drug or supplement that could halve the number of sick days you take due to such upper-respiratory infections as the common cold? It would make some pharmaceutical company billions of dollars. But there is already something that can boost your immune system for free and by so much that you can achieve a 25–50 percent reduction in sick days. And it has only good side effects. What is it?
Exercise.51
What’s more, it doesn’t take much of a workout to get results. Studies find that if you let kids run around for just six minutes, the levels of immune cells circulating in their blood increases by nearly 50 percent.52 At the other end of the life cycle, regular exercise can also help prevent age-related immune decline. One study found that while elderly, sedentary women have a 50 percent chance of getting an upper-respiratory illness during the autumn season, those randomized to begin a half-hour-a-day walking program dropped their risk down to 20 percent. Among conditioned runners, though, the risk was just 8 percent.53 Exercising appeared to make their immune systems more than five times better at fighting infection.
So what’s going on here? How does the simple act of moving decrease the chance of contracting an infection? Approximately 95 percent of all infections start in the mucosal (moist) surfaces, including the eyes, nostrils, and mouth.54 These surfaces are protected by antibodies called IgA (short for immunoglobulin, type A), which provide an immunological barrier by neutralizing and preventing viruses from penetrating into the body. The IgA in saliva, for instance, is considered the first line of defense against such respiratory-tract infections as pneumonia and influenza.55 Moderate exercise may be all it takes to boost IgA levels and significantly reduce the chance of coming down with flu-like symptoms. Compared to a sedentary control group, those who performed aerobic exercises for thirty minutes three times a week for twelve weeks had a 50 percent increase in the levels of IgA in their saliva and reported significantly fewer respiratory infection symptoms.56
While regular physical activity improves immune function and lowers respiratory infection risk, sustained and intense exertion may have the opposite effect. As you go from inactive to active, infection risk declines, but at a certain point, overtraining and excessive stress can increase the risk of infection by impairing immune function.57 In the weeks following marathons or ultramarathons, runners report a two- to sixfold increase in upper-respiratory-tract infections.58 Within a day of starting an international competition, elite soccer players were found to suffer a significant drop in their IgA production.59 This drop has been tied to upper-respiratory-tract infections during training. Other studies have found that IgA levels can drop after even just single bouts of overstrenuous exercise.60
What can you do, then, if you’re a hard-core athlete? How can you reduce your chance of infection? Traditional sports medicine recommendations don’t appear to have much to offer: They’ll tell you to get a flu jab, avoid touching your eyes or picking your nose, and stay away from sick people.61 Gee, thanks. The reason these steps may be insufficient is that respiratory infections are often triggered by reactivations of latent viruses already inside the body, such as Epstein-Barr virus, the cause of mononucleosis. So even if you never came in contact with anyone else, as soon as your immune function dips, these dormant viruses can return and make you sick.
Thankfully, a number of foods may help maintain your immunity to keep the germs at bay.
First up is chlorella, a single-celled, freshwater, green algae typically sold as a powder or compressed into tablets. Researchers in Japan were the first to show that mothers given chlorella saw increased IgA concentrations in their breast milk.62 Although chlorella extract supplements failed to boost overall immune function,63 there is evidence that whole algae may be effective. In a study out of Japan in 2012, researchers rounded up athletes ripe for infection during the middle of training camp. Among the control group, who received no supplements, IgA levels dropped significantly during intense exercise. But among those who were given chlorella, IgA levels remained steady.64
One note of caution: A disturbing case report from Omaha, Nebraska, was published recently, entitled “Chlorella-Induced Psychosis.”65 A forty-eight-year-old woman suffered a psychotic break two months after starting to take chlorella. Her physicians told her to stop it and put her on an antipsychotic drug. One week later, she was fine. Chlorella had never before been linked to psychosis, so they initially presumed it was just a fluke. In other words, the psychosis may have just coincidentally begun after the woman started taking chlorella, and the reason she felt better after stopping it may have just been due to the drug kicking in
. But seven weeks later, she was still on the drug and had restarted taking chlorella—and she became psychotic again. The chlorella was stopped, and her psychosis resolved again.66 Perhaps it wasn’t the chlorella itself that triggered the episode but some toxic impurity or adulteration. We don’t know. Given the scandalously ill-regulated supplement market, it’s hard to know what you’re getting when you try to buy “food” in supplement bottles.
Another option for athletes who want to sustain their immune function is nutritional yeast. A 2013 study reported that you may more effectively maintain your levels of white blood cells after exercise by consuming a special type of fibre found in baker’s, brewer’s, and nutritional yeast.67 Brewer’s yeast is bitter, but nutritional yeast has a pleasant, cheese-like flavor. It tastes particularly good on popcorn.
The study found that after two hours of intense cycling, the number of monocytes (another type of immune system white blood cell) in subjects’ bloodstreams took a dip. But those who were given the equivalent of about three-quarters of a teaspoon of nutritional yeast before they exercised ended up with even higher levels of monocytes than when they started working out.68
That’s all well and good on a lab report, but does consuming yeast fibre actually translate to fewer illnesses? Researchers put that question to the test at the Carlsbad Marathon in California.
Runners who were given the daily equivalent of about a spoonful of nutritional yeast in the four weeks after the race appeared to have just half the rates of upper-respiratory infection compared to runners consuming a placebo. Remarkably, the runners on yeast reported feeling better too. When asked how they felt on a scale of one to ten, with ten being the best, the people taking the placebo reported about a four or five. On the other hand, the subjects on the nutritional yeast consistently reported feeling better, around a six or seven. Elite athletes normally experience mood deterioration before and after a marathon, but this study revealed that a little nutritional yeast may improve a wide range of emotional states, reducing feelings of tenseness, fatigue, confusion, and anger, while at the same time increasing perceived “vigor.”69 Pass the popcorn!
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