Your coworker sneezed on the printer. A friend’s kid is down with the flu. You’re about to take a 12-hour plane ride—in a middle seat. So you stock up on purported immune-boosting foods like oranges, ginger, and garlic, hoping to ward off bugs.

Good for you. AĚýhealthy diet can keep your immune system (and every other system) humming along smoothly, says , a registered dietitian nutritionist who works at the Mayo Clinic. Flavorful ginger and garlic don’t hurt either, especially if you use them to seasonĚýwhole foods. But if you think these foods will transform you into some sort of antiviral superhero, you’re wrong. The link between food and immunity is far less clear than most of us have been led to believe. (At şÚÁĎłÔąĎÍř, we’ve been guilty of overstating that connection in the past, too.*)

No food has the power to magically boost immunity, according to immunologist , director of the Center for Clinical Immunology at the Cleveland Clinic’s Department of Rheumatic and Immunologic Diseases. The idea that “dietary manipulation alone can reduce your coldsĚýor fluĚýduring a given season—I know of no evidence of that,” he says.ĚýOf all the choices you can make—eating well, sleeping enough, exercising, and reducing stress—food probably plays the smallest role in fighting off infection, he says.

Being deficient in an essential nutrient, like zinc or vitamin E,Ěýcan decrease your resistance to invading microbes, but that does not necessarily mean that increasingĚýyour intake of that nutrient will directly impact your immune system if your levels are normal, says , the lab director and senior scientist at Tufts University’s Nutritional Immunology Laboratory.

You would have to carefully track the effect of increased intake over time to definitively demonstrate theĚýrelationship, and reliable nutritionĚýresearch is difficult to conduct. Consider a six-week Ěýthat Meydani’s group recently conductedĚýon whole grains (which, though they aren’t widely considered immune boosting, showed modest improvements in biomarkers of immunity and gut bacteria). She and her colleagues had to prepare every meal for about 80 participants—half with whole grains, half with refined—and collect fecal samples to analyze bacteria. That’s an expensive proposition, and food manufacturers who might fund these studies typically have smaller research and development budgets than pharmaceutical companies, she says.

The current evidence for common curative foods is far from definitive, so before you start chugging superjuices, check out the research—or lack thereof—behind the most popular cold-fighting foods.

Citrus Fruits and Juices

Yes, they’re rich in vitamin C—which does play a in immune health, potentially by speeding up the rate inĚýwhich pathogen killers called develop. But again, just because vitamin C plays a part in our immunological defenseĚýdoesn’t mean consuming more than the recommended amountĚýwill make us stronger, says Colleen DeBoer, a clinical dietitian at Northwestern Medicine’s Lake Forest Hospital. A comprehensive Ěýby medical research nonprofitĚýCochrane from 2013 found no data to justify megadoses of vitamin-C supplements, with the possible exception of people under extreme stress, such as marathoners and soldiers in subarctic climates (and you’re not going to get that much from a morning glass of OJ or a few clementines anyway).

Ginger

In the lab, extracts from this spicy root respiratory bugs from infecting cells from human airways. And in some studies, ginger and derived from itĚýreduced influenza and other infections. This type of research is a step towardĚýunderstandingĚýa compound’s effects, but “we need to do these studies in humans in order to be able to show that it’s effective,” Meydani says. Human trials show some support for ginger when it comes to other ailments, , butĚýnot for infectious diseases.

Garlic

Garlic’s infection-fighting properties also don’t pass scientific muster, at least not yet. A CochraneĚýĚýof research published in 2014 found just one rigorous study of garlic as a cure for the common cold. The single trial did show a benefit in terms of warding off illness; people who took a garlic tablet every day for three months reported half as many colds as people who took a placebo pill instead. ThatĚýmight warrant further research,Ěýbut it’sĚýfar from definitive. According to Meydani, more studies need to show similar results, with a variety of people and in a variety of circumstances, before researchers can honestly tout garlic’s powers.

Chicken Soup

In 2000, researchers at the University of Nebraska Medical Center Ěýthat included plenty of root vegetables and a whole baking chicken, plus a pack of wings. One way colds cause respiratory symptoms is through inflammation, which occurs when viruses trigger a cascade of immune cells to your airways; in the , the soup seemed to act as a mild anti-inflammatory, calming the movement of some of these cells, called neutrophils, in chambers in the lab. That—and the mere fact it’s a hydrating hot liquid—might make you feel better temporarily, but there’s no evidence it can shorten the duration of your infection. Besides, a single study in the lab isn’t proof something works in the real world, Meydani says.

Zinc

Of all the rumored immune enhancers, zinc has the most evidence on its side. A meta-analysis last year crunched the numbers from seven placebo-controlled trials and found that high-dose zinc lozenges shortened the duration of the average cold by about one-third. But those same high doses can unpleasant side effects, including nausea and vomiting, and can also interfere with prescription drugs like antibiotics and blood-pressure medications. They likely work best in people with low zinc levels to begin with. (ApproximatelyĚý30 percent of older adults have zinc deficiencies, according to research Meydani conducted.)ĚýYou can ask your doctor about a blood test to determine your zinc levels.

As the cold and flu season drags on, the bottom line is: what you eat on a regular basis matters far more than any food you rush out to buy at the first sign of a sniffle, DeBoer says. A whole-foods diet that includes plenty of vegetables, fruits, whole grains, and fish is likely to provide all the vitamin C, zinc, and other nutrients you need to shore up your defenses, according to Zeratsky. The Mediterranean diet is a good place to start. It might even supply you with antioxidants and other helpful compounds that haven’t been identified yet.

*In 2014, we published a story titled “5 Top Flu-Fighting and Cold-Crushing Foods.” That page on our site now redirects to this one, because we believe that this piece provides more accurate service to our readers.

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Elite ultrarunner ran his first race in Chamonix, France, in 2004. He had trained hard for the uphills—runners gain 30,000 feet of elevation over the 100-mile course—but failed to prepare for the plunging downhills, including a nearly 2,375-foot drop between miles 45 and 48. Ultimately, it was the relentless pressure of the descents that wore him down the most during the race, leading Millet to a 28-hour, 35-minute finish, nearly 7.5 hours longer than the winner.

The next year, Millet altered his training to include a focus on downhills, repeatedly riding a ski lift to the top of a mountain and running down the slopes. He was rewarded with a fourth-place finish, clocking in at 23:45:24. “Definitely, that [downhill training] was the main difference between the two races,” says Millet.

Downhill running puts a heavy load on your legs, including higher chances of muscle damage and other injuries. Careful and specific preparation is a must for any runner attempting a course with a considerable downhill component, be it a trail race like the UTMB or a road race like the Boston Marathon.

We asked Millet and , a San Diego–based running coach and a sub-three-hour finisher at this year’s Boston Marathon, for their best tips on training up to go down.

The Downhill Difference

versus down an incline is practically an entirely different sport, Millet says. “If you run downhill and uphill, this is as different as cycling and running, for me.”

When you head uphill, your muscles work hardest when they shorten as you straighten your leg and push off the ground—this is known as a concentric contraction. Heading down, on the other hand, involves almost exclusively eccentric contractions. Your leg muscles engage when they’re in a lengthened and stretched position as you bend your knee before it hits the ground and absorbs the impact, making them more prone to microtears and damage. That’s why courses with early downhill sections like Boston hit your quads hard, causing delayed fatigue mid-race or increased soreness in the days after.

What’s more, your center of mass shifts as you descend, instinctively causing you to lean backward and try to slow yourself down. But hitting the brakes too hard actually worsens the impact on your muscles, joints, and bones as you essentially fight your body weight on the way down. In fact, downhill running increases impact forces by 54 percent compared to level running, in the Journal of Biomechanics—a surefire way to wear out your muscles quickly.

“Naturally your body wants to protect itself against that gravitational pull, so it tends to hesitate,” Lizotte says. Running downhill well, she says, means “managing that hesitation so you’re still moving fluidly and efficiently, but not at a pace where you’re completely out of control.”

Refine Your Technique

Tweaking your form makes a big difference in reducing downhill’s detrimental effects, Millet says. Try to think of your movement down the slope like a controlled fall. Take short, fast steps and turn over your legs quickly. Focus on leaning slightly forward at the waist so your feet stay below your center of mass. Envision keeping your nose directly over your pubic bone and in alignment with your belly button, Lizotte recommends. This also prevents you from sticking your head out, a position that creates extra tension in your neck.

Practice Pays Off

Protect your body by taking advantage of the repeated bout effect—the idea that even brief exposure to eccentric contractions helps your muscles resist damage and soreness the next time around, Millet says. In short, that means that you can specifically train for downhill running and see improvements in your performance as well as better injury protection as a result.

If you’re completely new to downhill running and strength training, any sort of lower-body weight training you do will build strength and therefore resilience in your legs as you tackle descents. But you’ll get the most from moves such as single-leg deadlifts, hamstring curls, and calf raises done with an emphasis on the eccentric or lengthening portion of the movement by slowing your motion during that phase of the lift.

Best of all, though, is just to get out there and move down some hills. Start with hiking a descending route wearing a backpack, Millet says. Then progress to doing some easy runs on hillier courses, focusing on your downhill technique. Once you’re comfortable there, add a couple minutes of race-pace running on the descent to familiarize yourself with how the effort will feel during your event, Lizotte says. Another option: Work in a few 10-to-15-second downhill sprints at top speed, which will improve your technical skills on downhills and make race pace feel easy by comparison, Millet says.

Given the extra beating your muscles take during downhill work, it’s critical to leave plenty of days in between downhill days to recover. Begin with one workout every three weeks, gradually progressing as your body adapts and soreness decreases.

Even at your peak, once a week or so is probably sufficient to maximize the gains of downhill training without creating excess injury risk, Lizotte says. “Interjecting it throughout the training plan will help. It doesn’t take a lot,” she says. If you don’t live in a hilly spot, you can supplement your training with fast intervals and drills like butt kicks and high knees on flat land, Lizotte says. These types of workouts will improve your turnover and build quad strength even without having downhills for practice.

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