Spirulina, a blue-green algae available in powder, flake and tablet form, could enhance muscular strength and athletic endurance.

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As a runner, cyclist, or someone trying to bulk up, you’ll likely respond to a headline hailing red wine, raw honey, or apple skins as the new secret to stamina. You fervently snack on apples, dip into the honey jar, enjoy a second glass of wine with dinner, and wait to feel the effects — and wait and wait.

“It’s not that they don’t work, it’s that you’d have to take a lot to reach concentration levels necessary to achieve an erogenic effect,” says Tricia Bland, RD, a spokesperson for the American Council on Exercise. So forget about getting an endurance boost from what’s in the fridge — researchers conclude that you would need to chow down on 100 apples or drink 100 glasses of red wine in a single day to experience the erogenic effects found in various studies.

This leaves you with the prospect of trying dietary supplements, which can get a little scary. Many over-the-counter varieties are not regulated by the FDA, so purity and concentration vary by manufacturer, notes Bland. The key to being smart about integrating new science into your sport is to be skeptical, says Bland. Because research around natural endurance enhancers can get complicated, we put Bland’s advice to the test and took a look at seven compounds that claim to help you run farther, cycle longer, and lift more weight. Here’s what we found.

Caffeine

A mild central nervous system stimulant found in coffee, tea, yerba mate, soft drinks and chocolate, caffeine keeps you awake and wards off fatigue. Research suggests that these everyday benefits could extend to sports performance, lowering one’s perception of intensity or difficulty and allowing athletes to exercise at a higher intensity for a longer period of time. How it works: Caffeine causes free fatty acids to be released from the liver, which are then converted to usable energy, enhancing aerobic performance, says Bland.

Should you try it? Compared with the rest of the endurance enhancers here, caffeine is probably your best bet, says Bland.

“It’s the only compound that has been shown to be an erogenic aid and is currently allowed (in quantities less than 12 mg per liter of urine) by the International Olympic Committee,” says Bland, noting that the IOC did ban caffeine until it became prevalent in over-the-counter medications like Excedrin. Still, caffeine isn’t for everyone — especially on race day. Aside from giving you the jitters or an upset stomach, caffeine is a diuretic, which can lead to dehydration if you drink more than 5 cups and don’t replace fluids fast enough on a hot day.

Raw Honey

Honey is a mixture of sugars, primarily fructose and glucose and water. While processed honey is stripped of many vitamins, amino acids and enzymes, raw honey maintains many of the nutrients found in the hive. Research suggests that honey may be a good carbohydrate source for endurance athletes because it breaks down and raises blood sugar more slowly than many other sugars.

Should you try it? “Honey has great properties (as an antioxidant and an antimicrobial), but to say it’s going to increase performance over other sugars? No,” says Bland.

Asian Ginseng

Asian ginseng, or pantax ginseng, may be purchased as root powder in supplement form or found in energy drinks as an extract. Used in traditional Chinese medicine, Asian ginseng is classified as an adaptogen, an herb that is believed to increase resistance to stress and fatigue.

Should you try it? Although most researchers conclude that ginseng is generally safe for consumption, herbal supplements should always be taken under the supervision of a health care provider.

“People need to understand that many medications are derived from plants, so even though we call (herbal supplements) natural, they can have very deleterious effects on our bodies when consumed in high doses or in combination with other medications,” says Bland.

In particular, ginseng should not be combined with heart, blood pressure, blood thinning or diabetes medications or along with certain antidepressants.

Nitrates

Nitrates have a bad rap as the cancer-causing compounds hiding in cured meats, like bacon, sausage and hot dogs. But an even bigger source of nitrates than bologna comes from vegetables like red beetroot, lettuce, celery and spinach — superfoods that can actually reduce cancer risk. The explanation: Carcinogens form when nitrates react with compounds found in meat protein, but when nitrates mix with vitamin C and other antioxidants found in veggies, they are far less likely to be harmful.

Should you try it? Bland says the real benefit of beetroot juice comes from the immune support it provides.

“It’s a very potent antioxidant, rich in calcium, iron, vitamin A, vitamin C, folic acid and fiber. It helps in cell membrane repair and prevents breakdown more than it helps with increased speed and endurance,” she says. Also, be warned that the purple elixir can get pricey. A half dozen 16.9-ounce bottles can set you back close to $40, or roughly $7 for each 500 mL serving.

Quercetin

Quercetin is an antioxidant found in fruits and vegetables, particularly concentrated in the skins of red apples, red onions, berries and grapes. It is also available in supplement form. Science suggests that quercetin may increase energy-producing mitochondria in muscle and brain cells, boosting mental and physical endurance during exercise.

Should you try it? For practicality’s sake, quercetin may not be the magic bullet for your next century bike ride. You’d need to eat 100 apples or guzzle three cans of FRS Healthy Energy, a quercetin-containing sports drink, to reach 1,000 mg. But don’t dismiss apple skins and red onions just yet — they offer serious protection at the cellular level, says Bland.

“When we reach a higher VO2 max, we have a higher accumulation of free radicals (in our bodies) because of the increased volume of oxygen we’re taking in,” she says, and powerful antioxidants like quercetin scavenge free radicals, which can damage cell membranes.

Resveratrol

A quercetin cousin, resveratrol is found in grape skins and red wine, and becomes more concentrated as grapes ferment during the winemaking process. Another potent antioxidant, researchers have linked resveratrol to improvements in longevity, fat-burning and athletic endurance.

Should you try it? Before knocking back a few extra drinks the night before your race, consider this: So far, resveratrol studies largely have been limited to mice, and scientists are just now starting to test the supplement’s effects on humans. Picking red wine over hard alcohol has its health benefits, like potentially lowering bad cholesterol and fighting belly fat, while no such research exists on hard alcohol, notes Bland. Still, endurance athletes should drink in moderation: “Alcohol is very dehydrating and not the type of sugars we are looking for when it comes to performance,” says Bland, explaining that complex carbohydrates, like whole grain bread, brown rice and oatmeal, are better sugar sources for runners and cyclists.

Spirulina

Spirulina, a blue-green algae available in powder, flake and tablet form, is very high in protein, which researchers suggest could enhance muscular strength and athletic endurance.

Should you try it? Given its mix of protein, amino acids and vitamin B12, spirulina is an excellent dietary supplement for vegetarians, says Bland, noting that 60 to 70 percent of the plant’s structure is composed of protein. But as an endurance enhancer, Bland is less of a believer.

“It can benefit you with an immune-enhancing effect, but not a muscular- or strength-enhancing effect,” she says, explaining that the supplement may help you get sick less often, but that you shouldn’t start taking spirulina and expect to run or cycle longer. “It’s more of a systematic health enhancement.”