Convenient foods and supplements purport to boost energy and help competitors train harder. But do they work?
The body of an endurance athlete is a finely tuned engine, and glycogen—a polysaccharide stored in the muscles and liver—is its fuel. When an athlete runs low on her energy supply, what may seem like sure victory can quickly turn to frustrating defeat.
“It feels like that movie of a robot running out of power—it starts walking and talking very slowly. It’s gradual at first, but if you don’t fuel up, it’s curtains,” says mountain bike and cyclo-cross racer Serena Bishop Gordon.
Last summer, Gordon was the first female finisher in the High Cascades 100, a 160-km mountain bike race held in Central Oregon. The 37-year-old finished the course in a bit over eight-and-a-half hours. She credits sticking to her nutrition plan—including during the race—for the win. “As I’ve gotten to become a better athlete, planning my diet has gotten more and more important.”
Elite athletes may be born with the right genes, but the factors under their control are diet and how much they train. For starters, all athletes eat regular meals of nutritious foods. Many also turn to specialty foods and supplements to provide extra energy, aid in recovery from training and events, and ward off injury and illness.
Many products purport to boost athletic performance beyond what can be achieved through genes, training, and diet. But, as is the case for nutritional supplements more broadly, clinical evidence supporting those benefits is often slim. In addition, what works well for one athlete may not work at all for another. There is always a new product or substance to try, but even athletes willing to sort through the data can’t be sure they will get their money’s worth.
The sports nutrition market in the U.S. grows at about 5% annually and reached $6.3 billion in 2014, according to Christopher Shanahan, analyst at the market research firm Frost & Sullivan.
Sports nutrition products are selling better than ones aimed at other benefits such as heart health, Shanahan explains. As large clinical trials on health supplements have come to contradictory conclusions, “growing consumer skepticism has stunted the growth potential,” he says.
In contrast, industry experts and athletes say sports nutrition products enjoy a high degree of loyalty. If users of a product feel they can detect a difference in performance—if it seems to help them run faster or longer—they’ll stick with it. Compared with a supplement that may improve heart health over a decade, performance products are judged by athletes whether they provide benefits over the course of weeks or days.
The centerpiece of sports nutrition is protein powders—a commodity product that makes up two-thirds of the market, according to Shanahan. Protein products are all positioned to help athletes build muscle mass.
In the second-largest category are products designed to boost energy and enhance endurance. They contain common substances such as caffeine and sugar, as well as specialty ingredients including amino acids, specialty carbohydrate molecules, and plant extracts.
Another category is so-called “recovery” products. They contain carbohydrates and protein, or substances designed to aid in muscle repair or decrease inflammation.
Products featuring newer specialty ingredients such as quercetin, a plant flavonoid purported to have wide-ranging performance benefits, make up only 3–5% of the market, Shanahan says. But new or specialized molecules are what drive trends in the industry and help brands differentiate their offerings on crowded retail shelves.Checking the Evidence
Competitive athletes learn about nutrition products in sports magazines, by word of mouth from training partners, and from product showcases at events. But in recent years, information from clinical studies has played an increasingly important role in marketing. Study results can lend scientific credibility to what might otherwise be questionable claims.
Clinical trials in sports nutrition are generally done at universities with nutrition and sports physiology departments. They may be sponsored by a nutrition company. Compared with research done on potential drug or health supplement candidates, the studies tend to have a small number of participants—generally 12 or fewer.
“That is often the major criticism of the studies,” says Edward P. Weiss, associate professor of nutrition and dietetics at Saint Louis University. Weiss, though, is okay with the numbers. “One of the strengths, in a sense, is if the effect is powerful enough then you only need a few subjects to make fairly definitive conclusions.”
The majority of Weiss’s research is on weight loss, diabetes, and cardiovascular disease and is supported by the National Institutes of Health. Independent funding for research on healthy people is quite rare, in contrast. But Weiss is also a bicycle racer, and his “extracurricular” research is often aimed at testing hypotheses about, for example, substances that increase blood flow to muscles during exercise.
As with other health studies, a quality sports nutrition investigation will be randomized, blinded, and placebo-controlled. Often a crossover study is done where each participant is tested twice—once with the target and once with the placebo—separated by a period of time for the substance to clear the body.
Weiss explains that sports nutrition studies come in two flavors. They may be mechanistic, based on biopsies or blood tests showing inflammatory biomarkers, for example. Or they can be based on performance indicators such as time to exhaustion or to finish a 80-km ride on a stationary bike.
“Of course the real measure is if it actually provides performance improvement,” Weiss asserts. Yet studies on biomarkers—which are more expensive to perform and don’t measure performance improvements—are favored by journal reviewers and therefore dominate the literature, he laments.
The performance studies that Weiss’s lab carries out find some products that work and some that don’t.
His team recently conducted a study on a combination of plant-extract nutrients that was found in previous research to inhibit inflammatory pathways. The researchers concluded that the extracts had absolutely no effect on exercise performance. “The mechanism was there, yes, but athletes got no benefit from it,” he says.
In another study, the Weiss team found that consuming baked beets—which contain a strong dose of nitrates, consumption of which has been linked to improved exercise performance—improved running performance in 11 men and women. The subjects in the crossover test ran 5 km on a treadmill and were timed. Those who consumed beets ran 5% faster during the last 1.8 km of the race and reported lower perceived exertion.
Nitrates are converted to nitric oxide in the blood, Weiss explains. Nitric oxide acts as a vasodilator: It relaxes blood vessels, increasing their diameter and shuttling more glycogen and oxygen to muscles.Going the Distance
At the starting line, an athlete has about 1,800 to 2,000 calories, one day’s worth, stored as glycogen in the muscles and liver. During exercise, both organs convert it to glucose, which muscle cell mitochondria use to produce energy in the form of adenosine triphosphate (ATP). The body can also burn fat for energy, but that process requires oxygen, which is in short supply during high-intensity activities.
Training or race events lasting more than an hour trigger the liver to dump glucose to maintain blood sugar levels. That energy supply must be replaced for the athlete to keep going. The need for energy while on the run—or on the bike—is responsible for the proliferation of sugary sports drinks, bars, gels, and even jelly beans marketed to high-intensity athletes.
Gordon, who is sponsored by Clif Bar, a brand of energy products, says the main benefits of packaged products are convenience and ease of digestion. “Though it’d be great to have a turkey sandwich, it’s hard to carry, it’s hard to eat, and your body has to use a lot of energy to process it,” she says.
Even when consuming scientifically formulated energy foods, racers are hard-pressed to scarf enough fast-acting carbohydrates to propel them to the finish line. During a triathlon, for example, competitors may burn up to 800 calories per hour, but most can take in only 400 at best. And the carbohydrates can cause bloating and other forms of intestinal distress.
Energy products are made with sugars such as glucose, fructose, and maltodextrin. Also used are more exotic specialty sugars like the disaccharide trehalose and designer molecules based on glucose. Maltodextrin, a linear chain of glucose molecules, is less sweet than other sugars and is used to make energy foods more palatable.
Until recently it was assumed that glucose delivers energy the fastest, because it’s what we use to make ATP. But manufacturers are now incorporating fructose as well. The body uses separate pathways to absorb glucose and fructose, and researchers believe that the combination means more sugars can be absorbed by the intestinal lining. The newest products by energy gel maker Gu, for example, are made with fructose and maltodextrin.
Athletes who want more calories but are concerned about bloating and other stomach distress can also turn to specialty carbohydrates. Vitargo Global Sciences produces a high-molecular-weight, highly branched glucose-based molecule. According to the company, studies show the molecule, also called Vitargo, absorbs less water, because of its low osmolality, and leaves the stomach faster than other forms of sugar.
The firm’s chief executive officer, Anthony Almada, says athletes can more closely match their calorie output with Vitargo. “Most notice a difference after a single dose,” he claims. “They say, ‘I don’t feel tired after; I felt like I could have gone another hour.’ ” He acknowledges the benefits vary by individual.
In addition to sugar, energy products may also contain salt to replenish electrolytes and metabolic boosters such as caffeine and the amino acids l-glutamine and carnitine. Some come with plant-based substances that promise to boost ATP production, such as citrulline from watermelon and extracts from green tea.
Food scientist and self-described “gym rat” Danielle Robertson is passionate about energy drinks and reviews them on her blog. She explains that caffeine, when consumed 30 minutes before a workout, boosts mental energy and may improve focus. Studies show that the equivalent of one to two cups of coffee helps athletes train longer.
“But not all products have a reasonable amount of caffeine—a lot have way too much in one serving. Or they have other ingredients that either don’t do anything or should not be in there with caffeine,” she says.
Other ingredients that Robertson tracks include β-alanine, an amino acid thought to delay muscle fatigue by buffering lactic acid buildup, and quercetin, derived from beets and other dark vegetables, which can provide energy in place of caffeine. Studies on quercetin are still preliminary but suggest it also may inhibit inflammatory response that contributes to fatigue and soreness.Recovery and Repair
Although moderate exercise improves overall health and immune function, prolonged high-intensity training can stress the nervous system, trigger inflammation, damage muscles, and depress immune response.
So it’s no surprise that competitive athletes look to specialty foods and supplements to help them bounce back and maintain their training regimen. Many high-endurance events attract comparatively mature athletes, whose bodies take more time to recover.
“Often the harder and longer the event, the older the crowd,” observes Robert Kunz, vice president of science and technology for supplement maker First Endurance. “A 160-km ultrarunning race in the mountains is the hardest event you can do, and most of the people are in their 50s.” Although it is difficult to increase strength as we age, it is possible to increase endurance, Kunz explains.
John Staley is a 65-year-old national champion trail runner who specializes in half- and full marathons. All runners have an Achilles’ heel, and Staley’s is his knees. Inflammation from running has led to three knee procedures, so he’s a fan of supplements purported to have anti-inflammatory effects.
One he swears by is grape seed extract, rich in several antioxidants, which he says works well to protect his knees from damage. “I can run huge distances if I am faithfully taking the grape seed supplement,” Staley says. The Food & Drug Administration, however, has not approved claims that the supplements boost the immune system or prevent or repair joint damage.
He also takes glucosamine sulfate, which FDA agrees has been shown to support joint health, and omega-3 fatty acids to speed healing from cuts and bruises sustained on the trail. Studies on athletes show that omega-3s also help decrease muscle soreness and reduce swelling after damaging exercise, though this is not indicated on labels.
At First Endurance, Kunz observes professional bike-racing teams to learn about the impacts of training stress. “It makes it hard to sleep at night,” he says, “and training and performance plateaus—and maybe starts getting worse.”
The body responds to stress by releasing the hormone cortisol, which fights inflammation in the short term. But in the long term, elevated levels of cortisol can actually cause inflammation. The hormone can also weaken the immune system, break down muscle protein, and reduce bone formation. Kunz says his firm’s products are primarily aimed at modulating cortisol.
The two main ingredients in the First Endurance product Optygen are extracts of an herb, Rhodiola rosea, and a mushroom called Cordyceps sinensis. Both grow in high-altitude Tibet where locals use them in tea; they are purported to aid in oxygen transfer and help clear lactic acid from muscles. According to the company, a South Dakota State University study showed Optygen reduced cortisol levels by 26%.
Much of the research that the firm cites about the extracts themselves comes from studies of traditional herbal medicine published in Chinese and Russian journals. A search of PubMed also turned up two studies that suggest the two extracts improve aerobic and endurance exercise performance.
Foods and beverages marketed to aid in recovery commonly contain a roughly 3-to-1 ratio of carbohydrates to protein to restore depleted glycogen and provide the raw material for muscle repair. One favorite is old-fashioned chocolate milk. A new entrant for muscle recovery is tart cherry juice, which studies suggest may lessen pain and weakness after endurance events by reducing inflammation and oxidative stress.
Another recent trend is the addition of the branched-chain amino acids leucine, isoleucine, and valine. The so-called BCAAs have been used in medical interventions for muscle disorders. They stimulate the building of protein in muscles and may reduce muscle breakdown. A 2015 study showed that 10 weeks of BCAA supplementation improved power output in trained endurance cyclists (Amino Acids, DOI: 10.1007/s00726-015-2125-8).
Antioxidants, omega-3 fatty acids, and BCAAs also strengthen the immune system. Hard training leaves athletes more susceptible to upper respiratory tract infections than moderate exercisers. A 1990 study of runners signed up for a marathon showed that those who competed in the race were six times as likely to report an infection comparedwith those who missed the race (Br. J. Sports Med. 2005, DOI: 10.1136/bjsm.2004.017194).Downsides and Dangers
The most common drawback of performance foods and supplements is that they may be a waste of money. They tend to be pricey, commonly costing around $85 for a month’s supply, and they may not work for all athletes. Products that have been shown to boost endurance in young men may not have the same benefit for older women, for example.
Another concern is that new or uncommon substances may not have a track record for safety, Saint Louis University’s Weiss warns. In particular, ingredients that purport to build muscle and burn fat can cause unwanted health effects.
In 2004, FDA banned the stimulant ephedra from dietary supplements because it was shown to raise blood pressure. One new herbal ingredient on the market, p-synephrine, made from the bitter orange fruit, has a similar structure to ephedra.
And athletes must make sure that anything they consume does not contain performance-enhancing substances banned by their sports’ governing bodies. Third-party certifiers such as NSF International test products for banned substances, which can appear because of cross-contamination at manufacturing plants.
At the University of Nebraska, a team of three sports nutritionists councils the school’s 560 athletes on how to best use foods and supplements and avoid banned substances. “We’re a food-first place. I don’t even talk about other supplements until I know their diet is solid,” says Lindsey Remmers, Nebraska’s director of sports nutrition.
“We do evaluate supplements for athletes. If the science supports it, we’ll recommend it. If not, it’s probably not worth their money,” Remmers says. “There are thousands of different functional ingredients added to foods to appeal to athletes. It’s our job to look through them and be the voice of reason.”
She relies on studies in peer-reviewed journals when making such recommendations. “I look for review articles—I’m not going to judge based on just one study.”
Several Huskers athletes have been trying trendy beet juice and BCAAs, Remmers says. She knows they are taking them but is not ready to advocate for them yet. In addition to reading the literature, she says, she keeps a close eye on her athletes. “Are they getting stronger, faster, or slower, and how do they feel when on the court or out on the field?”
The beet craze will no doubt fade, but Remmers is sure to be confronted with a new crop of substances that her athletes will want to take to squeeze out that one additional second or pound out that one more kilometer.
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