WHEN THE GREEK RUNNER SPIRIDON LOUIS won the first Olympic marathon in 1896, he reportedly stopped along the route to consume wine, milk, beer, orange juice, and an Easter egg. Sports nutrition has come a long way since then, but figuring out what and when to eat and drink remains challenging. There’s plenty of competing information on how to fuel up before and during exercise, how to refuel afterwards, and whether dehydration is really such a bad thing. No discussion of sports nutrition is complete without a look at some of the powders and pills that claim to (legally) enhance physical performance. Despite hundreds of scientific studies, there’s little evidence to back up the claims made by most supplements. But there is some interesting research emerging regarding supplements like vitamin D and probiotics, which makes them worthy of a closer look.
Should I carbo-load by eating pasta the night before a competition?
The origins of the pre-race spaghetti dinner go back to pioneering Scandinavian studies in the 1960s. Researchers found that if you started depleting your carbohydrate stores a week before competition by exercising hard and eating only fat and protein, your body would “super-compensate” by storing extra carbohydrate in your muscles when you carbo-loaded in the final few days. This led athletes to adopt a difficult and often unpleasant week-long carbohydrate depletion-loading regime before competitions.
There was one key problem with the initial studies: they used untrained subjects. Later researchers showed that trained subjects depleted their carbohydrate stores through the daily act of training and gained no additional benefit from adding a depletion phase. An Australian study in 2002 took things one step farther, showing that you can maximize your carbohydrate stores by eating 10 grams of carbohydrate per kilogram of body weight for just one day, as long as you don’t exercise vigorously that day. Continuing on a high-carbohydrate diet for another two days did nothing to further enhance carbohydrate stores in the Australian study.
It’s important to note that 10 grams of carbohydrate per kilogram is a very large amount—far more than you’ll get from a simple pasta meal. In fact, researchers have found that most athletes fail to fully max out their carbohydrate stores. If you’re a 70-kilogram (155-pound) athlete trying to pack in 700 grams of carbohydrate, you’d need to eat about 10 plates of spaghetti. Even over the course of a full day, it’s difficult to eat this much without supplementing your regular meals with sports drinks and other concentrated sources of carbs.
Having a full tank of carbohydrates won’t increase your peak running, cycling, or swimming speed, but it should allow you to maintain your pace for a little longer before your carbohydrate stores are depleted and you “hit the wall.” As a result, there’s no particular benefit to carbo-loading for shorter events where you don’t have time to completely deplete your body’s stores. For exercise lasting less than about 90 minutes—researchers disagree about the exact threshold—you don’t need to carbo-load.
Even for longer races like marathons, the evidence isn’t as clear as once thought. In the studies that showed carbo-loading benefits, subjects often weren’t allowed to consume any carbohydrates during the exercise trial. In real life, though, you’re free to drink sports drinks or swallow gels during marathons or long tennis matches. When you’re allowed to top up your stores like this during the actual event, the evidence that carbo-loading helps is much weaker. And there’s a potential downside: when you store carbohydrates, your body stores water along with it, meaning that a successful bout of carbo-loading can add several pounds to your competition weight. How you should balance these pros and cons depends on your personal experience—whether your stomach can handle ingesting carbohydrates during a competition, whether you’ve “hit the wall” in previous competitions, and so on.
There is one other factor that a pasta dinner—or any day-before loading, for that matter—can’t handle. While you sleep, about half the carbohydrates stored in your liver as glycogen will be consumed to fuel your nervous system. These liver glycogen stores help maintain normal blood sugar levels and fuel crucial organs like your brain, which can’t access all the glycogen stored in your muscles. For that reason, top endurance athletes make sure they get up several hours before competition (no matter how early that is!) and eat some easily digested carbohydrates like a banana, oatmeal, or a bagel to top up their liver glycogen.
What should I eat to avoid stomach problems during exercise?
Your stomach gets 10 to 20 times bigger as it goes from empty to full, ultimately holding about four cups of food and drink on average. This is a neat trick, but can lead to problems during exercise if you’re not careful. Studies have found that as many as half of people who do sustained aerobic exercise suffer from gastrointestinal problems like cramping, nausea, or diarrhea. Others find that mistimed meals leave them dizzy or short of energy, or cause a stitch. By following a few simple guidelines, you can reduce the chances that you’ll run into these problems.
After you swallow a mouthful of food, it typically takes an hour or two to move through your stomach into your colon. (It will be 24 to 72 hours before it finally exits the body.) For this reason, it’s best to allow three to four hours between a meal and a hard workout. Researchers have found that intense training can speed up this “orocecal” (mouth-to-colon) transit time, probably because your stomach gets used to processing the large amounts of food necessary to keep up training. In one study at Indiana University, collegiate swimmers and distance runners consuming 4,000 to 5,000 calories a day had orocecal transit times as low as half an hour, while sedentary controls consuming less than 2,000 calories a day took as long as three hours. (These times represent the speed for the first mouthful; it may take much longer to process a full meal.) This means that as you get fitter, you’ll get better at moving food through your system while still absorbing as many nutrients.
If you still have food in your stomach when you start exercise, the digestion process will slow down as blood is diverted away from the gut to your working muscles. In sports like running, the constant up-and-down jostling of your stomach and its contents may contribute to the chance of a cramp. Stress can also slow digestion, so you need to allow extra time for food to clear the stomach if you’re nervous before a race.
Additionally, your choice of foods can make a big difference. Dietary fiber slows down digestion and also increases bulk in your colon by drawing in water—so you’re better off with white bread than whole-wheat for a pre-workout snack if you’ve been having GI problems. Foods high in fat also take longer to move through the stomach. Unfortunately, pre-workout carbohydrates come with problems of their own: some people experience an effect called “rebound hypoglycemia” after eating carbohydrates in the hour before exercise, resulting in dizziness, weakness, and sometimes nausea after 15 or 20 minutes of exercise. This happens because simple carbohydrates trigger a rise in insulin to reduce levels of blood sugar. Exercise also reduces blood sugar, so if you combine the two back to back, your blood sugar levels drop too low and you get light-headed.
One way to avoid rebound hypoglycemia is to abstain from carbohydrates for the hour before your workout. Or you can take the opposite approach: if you eat carbohydrates in the last five minutes before you start, your insulin levels don’t have time to spike, thus avoiding the problem. It also helps to stick to foods with a moderate or low glycemic index, which means they cause a slower rise in blood sugar. A banana, a bowl of oatmeal, or a piece of whole-wheat bread with peanut butter are good examples of foods with a moderate glycemic index.
Finding the approach that works best for you requires trial and error—and it may involve avoiding foods that don’t cause you any trouble under normal circumstances. For reasons that still aren’t entirely clear to researchers, long or intense bouts of exercise seem to make the digestive system hypersensitive even to very minor food intolerances. With careful experimentation, though, you should be able to find a few simple meals that your stomach can tolerate even under the toughest conditions.