The Paleo Diet for Athletes (7 page)

Excessive nutrients.
Related to the last cause is another: taking in food or drink that is excessively concentrated with nutrients. The greater the fuel’s nutrient content, the slower the stomach processes it. While physiology textbooks say that, on average, the stomach empties about 6 calories per minute, or 360 calories per hour, most long-distance athletes know it is possible to handle far more than that—perhaps as much as 600 calories per hour (and maybe even more in some large athletes). There seems to be a lot of variation in individual tolerance for food volume. Whatever your limit, slightly exceeding it for several hours will eventually lead to the stomach overfilling, with but one solution—puking.

Dehydration.
Excessive dehydration in the heat may also contribute to nausea. If fluid intake is well below one’s sweat rate for a long period of time, body fluids are shunted away from the digestive system to the skin (for cooling) and muscles (for work production). When that happens, the processing of fuel and fluids is reduced. In other words, the stomach’s emptying rate falls and whatever is taken in accumulates until the excess triggers nausea.

Saltwater ingestion.
In ocean-swim events, such as Ironman-distance triathlons or long-distance swimming, swallowing seawater may set up the athlete for nausea later in the event. “Seawater poisoning” occurs when the high sodium content of ocean water causes the stomach to shut down until the gut’s sodium content is diluted, preferably by drinking plain water. If the athlete does not gradually take in water to dilute the sodium, or if he or she takes in fuel in any form (including liquid), the body will make its own adjustments by pulling water from the blood and intracellular space into the stomach or by vomiting.

None of the above.
Your gut’s displeasure during a given event could be due to several of the above scenarios—or it could be caused by something altogether different, such as nervous excitement, food poisoning, exhaustion, or extreme heat. It may also be that your body, while in good shape, is not yet fully prepared for a long-distance event. An extreme event relative to your fitness level may simply overwhelm your body’s ability to cope.

The good news is that once you vomit, it’s likely that you’ll start feeling
better. But don’t get carried away by the newfound relief—the problem could soon come back to haunt you. At this point, slow down if you haven’t already, and begin sipping water to see how that is accepted. If your stomach seems to handle that for 10 to 20 minutes or so, progress to a diluted drink by mixing water and a sports beverage. Take in only 2 to 3 ounces over 10 to 20 minutes. Again, if that stays down, try a normally concentrated sports drink. At some point, you will know that the conservative approach is working and you can resume a greater intensity, but be cautious; your stomach may still be upset. Even though this may cost you time, it is better to finish than to make the DNF (did not finish) list.

HYDRATION DURING EXERCISE

Athletes are generally greatly concerned by dehydration. After a poor race performance, especially on a hot day, they are likely to blame the less-than-stellar experience on excessive loss of body fluids. Recent research is showing, however, that the level of dehydration necessary to affect performance is greater than formerly believed. The trend is toward accepting dehydration at some level as a normal condition of exercise. For example, the American College of Sports Medicine in 1996 concluded that athletes should prevent any level of dehydration by continually replacing all water lost during exercise. By 2007 the ACSM’s position had changed due to concerns about excessive drinking resulting in hyponatremia (discussed later in this chapter), a far worse problem than dehydration. They now advise athletes to restrict water losses during exercise to less than 2 percent. But even that is questionable.

The clinical evidence is not overwhelming that losing 2 percent of body weight due to sweat is harmful to your health or to endurance performance. In fact, field studies conducted on athletes at long-distance races in hot and humid conditions, such as the Ironman Triathlon World Championship in Kailua-Kona, Hawaii, find that athletes continue to
perform at very high levels with body-weight losses of 3 percent or even greater. Some exercise scientists point out that the most dehydrated athletes in a race are typically the first to finish. They certainly were not slowed down by body-weight losses of greater than 2 percent.

Body weight is not recommended as a way to determine your fluid needs. For, after all, while racing or training you don’t have the opportunity to weigh yourself to gauge fluid replacement needs. Nor can you use past experiences when you’ve weighed before and after exercise. There are many variable conditions when you are training and racing that impact fluid levels. Small changes in air temperature, humidity, wind speed, exercise intensity, exercise duration, altitude, hydration status at the start line, glycogen storage levels, and other factors affect how much fluid your body loses through sweat and breathing. Knowing that one set of such conditions caused a loss of a certain amount of body weight does not mean that all exercise will result in the same or even similar losses. So how should you gauge fluid losses to prevent what could be excessive dehydration?

The answer is simple: thirst. Somehow, athletes have come to believe that thirst is not a good predictor of their body’s fluid needs. It’s likely due to effective marketing by sports drink companies, which has been shown to have a great influence on what athletes believe about hydration. If thirst does not work for humans, then we would be the only species in the animal world to have such a condition. And it’s unlikely that as a species we would have flourished and spread around the world to so many extreme environments.

Early humans evolved while running and walking long distances in the heat of the dry African savannah while hunting and gathering. Water was not readily available. There were no aid stations. They drank just enough to maintain healthy fluid levels, but not necessarily body weight. The key to this delicate balance, now as much as 10,000 years ago, is the sensation of thirst. If you learn to pay attention to how thirsty you are and drink enough to satisfy it, you will no longer need to be concerned with body weight. Nor will you need a “drinking schedule,” which is, at best, based on flimsy conclusions about what the many conditions will
be during exercise. It’s actually quite simple: If you are thirsty, drink; stop drinking when you are no longer thirsty.

SODIUM AND EXERCISE

Let’s address another rehydration issue common in endurance sport—the need for sodium intake to maintain or even improve performance.

During exercise, as fluid is lost through sweating and breathing, the concentration of sodium in the body actually increases. The reason is because much more fluid than sodium is lost through sweating. One might sweat off around a liter of water during intense exercise on a warm day, but lose only a tiny amount of sodium. Normal body sodium levels are about 140 millimoles per liter (mmol/l) of water while the level of sweat is about 20 to 60 mmol/l.

So let’s say an average-size human body contains 40 liters of water when at rest and normally hydrated. That means it has stored away something like 5,600 mmol of sodium (40 x 140 = 5,600). If 1 liter of fluid is lost during exercise and with that 60 mmol of sodium is excreted (the high end or “salty” sweater), then the new sodium concentration is about 142 mmol/l (5,600 - 60 = 5,540 / 39 = 142.05). The concentration of sodium has risen, not declined. Guess what happens next after a sufficiently large rise in sodium concentration occurs? Your thirst mechanism kicks in and you drink water to dilute the sodium, bringing it back down to something closer to 140 mmol/l. A study by Hubbard and associates found that a rise of about 2 or 3 percent of plasma sodium concentration evoked a strong desire to drink.

So your sodium content becomes more concentrated during exercise as you sweat, not less, as we’ve been led to believe. In other words, you don’t need to replace lost sodium during exercise because the loss is inconsequential, while the volume of water lost is significant. But even if you did, the sodium content of most sports drinks is only 10 to 25 mmol/l, not enough to replace the loss. More than that makes the drink
unpalatable. The extracellular fluid in your body, where much of the sodium is stored, has about the concentration of seawater. If you’ve ever swallowed seawater, you know how nasty that would be as a sports drink.

Would
not
taking in sodium during a long race or workout impact your performance? Not according to the research. For example, a study by Merson and associates found that adding sodium to a sports drink did not improve performance in a time trial effort after 4 hours of exercise at a moderate intensity. Similarly, a study by Barr and associates found that sodium in a sports drink did not impact the ability to complete 6 hours of moderate-intensity exercise.

Should you take in sodium at all during a race or workout? There is no known downside to doing so. In fact, there may be a slight advantage, but not for the reasons we’ve been led to believe. A bit of sodium may improve the rate of absorption of both water and carbohydrate in the upper part of the small intestine. Sodium during exercise also is known to expand blood plasma volume, increasing the amount of blood pumped by the heart for each stroke. That’s a good thing. And after exercise, extra sodium may be needed to prevent dilution in the cells as water is taken in to recover from the slight dehydration that occurred. So the bottom line is that it’s okay to take in sodium during and after a race or workout.

HYPONATREMIA

The greater issue for the long-duration athlete is hyponatremia—low sodium concentrations in the body fluids. This can lead to not only poor performance but also acute health problems and even death. In recent years there have been two reported deaths in marathons related to over-hydration-induced hyponatremia. Both were back-of-the-pack runners who had been on the road for several hours. Studies of Ironman-distance triathletes have shown that many competitors experience mild levels of hyponatremia.

This condition is considered to be a sodium concentration level of less than 135 mmol/l by some experts. The most common way this occurs is through dilution of sodium stores caused by overdrinking during exercise. So the main issue is not replacing sodium, but rather not drinking too much fluid. Thirst is the key to this balance. If you drink only when thirsty and to a level that satisfies thirst, then you will not drink too much. Drinking as much as possible, which used to be a common tip for athletes, or drinking to a predetermined schedule during events lasting longer than about 4 hours, has the potential to cause hyponatremia.

Hyponatremia occurs when the sodium concentration of the blood is reduced to dangerous levels. It can result from prolonged vomiting or diarrhea or from taking diuretics; but in endurance athletics, it’s most commonly seen with excessive intake of fluid during long events. And the fluid doesn’t have to be water. The death of one of the two marathoners mentioned above occurred from overdrinking a commercial sports beverage. Even though these drinks have sodium as an ingredient, they do not maintain a healthy concentration if you drink to excess. Hyponatremia is extremely rare in events lasting less than 4 hours, but it’s common in competitions taking 8 or more hours to complete. In studies at the New Zealand and Hawaii Ironman Triathlons, events that take 8 to 17 hours to complete, researchers found that up to 30 percent of finishers experienced mild to severe hyponatremia.

How does this happen? In a mistaken belief that one cannot take in too much water during exercise, the athlete overhydrates and may even gain weight during the event. The problem is most common with slower participants because they have greater opportunity and more time to drink. (The fastest athletes are more prone to dehydration than to hyponatremia; they find it more difficult to take in fluids at their level of competitiveness, plus they spend less time on the course.)

It can be difficult to determine if you are experiencing hyponatremia because the signs come on slowly. Early symptoms include headache in the forehead, nausea, muscle cramps, lethargy, confusion, disorientation, reduced coordination, and tunnel vision. One sure sign of hyponatremia
is bloating. Look for puffiness and tightness around rings, watches, sock bands, and elastic waistbands. In extreme cases, the athlete may experience convulsions, unconsciousness, respiratory distress, or cardiac arrest. Because urination is greatly reduced or stops altogether when blood sodium concentrations are low, hyponatremia is often misdiagnosed as dehydration—and that can be a fatal error. If water intake is increased in a mistaken attempt to rehydrate the athlete, the condition worsens.

Let’s now examine the unique nutritional characteristics of workouts and races of various duration ranges.

EATING DURING 2- TO 90-MINUTE EVENTS

These are the shortest exercise sessions that qualify as endurance activities and include 800-meter through about half-marathon runs, sprint-distance triathlons, bicycle criteriums and time trials, some mountain bike races, 5-K to about 30-K cross-country ski races, and most rowing events.

What sets such events apart from longer-distance racing is the high intensity. At the pace the athlete is traveling, taking in solid food is out of the question and, thankfully, not necessary. The focus of nutrition during training or racing for these events, regardless of one’s speed, is on hydration, which is resolved by drinking enough to satisfy thirst.

Assuming adequate nutrition in the days and hours preceding a 2- to 90-minute session, the athlete’s body is well prepared with glycogen stores. The risk of bonking is quite low for experienced athletes. Novices and weekend warriors may need to assume their starting point for taking in carbohydrate is 60 minutes, because they don’t store as much glycogen in their muscles. There is no harm in novices or advanced athletes using a sports drink, regardless of the duration. Some research has even found performance benefits from the intake of a sugar-based fuel source in events lasting less than an hour. Interestingly, one study found that rinsing
one’s mouth with a sports drink and spitting it out improved performance in relatively short events. The mechanism for this isn’t understood and the research is contradictory.