[This article originally appeared in the
October 2000
issue of Northwest Runner
magazine.]
"And now," said the head track coach, "Coach Behr would like to
say something."
Coach Behr stepped forward, looked around at the crowd of athletes
gathered in front of him, cleared his throat, and said: "You aren't worth
a damn without a good breakfast!" And then he stepped back. End of
speech.
Those nine words, uttered at an otherwise uneventful team meeting,
comprised the entirety of Coach Behr's advice to the team in my four years
of college track. The man was nothing if not succinct. But is breakfast
really a necessity for athletes hoping to perform their best? And
while we're on the subject of race-day nutrition, what should athletes
consume during and after a long, hard workout or competition?
The following article will attempt to answer these questions using the
best scientific data currently available to us.
A variation on the breakfast question is this: is it helpful to
eat a high-carbohydrate snack 30 to 60 minutes before exercising? Early
work by David Costill and colleagues (Costill et al., Journal of Applied
Physiology 43: 695-9, 1977; Foster et al., Medicine and Science in Sports
11: 1-5, 1979) suggested that snacking in the 30- to 60-minute time window
could cause hypoglycemia (a drop in blood sugar) during exercise and
potentially hinder performance. However, since that time, many other
studies (reviewed by Hawley & Burke, British Journal of Nutrition 77:
S91-103, 1997, and by Williams & Chryssanthopoulos, World Review of
Nutrition and Dietetics 82: 33-45, 1997) -- including some carried out in
Costill's lab -- have indicated that small pre-race snacks either improve
or have no effect on endurance performance. Thus, although the threat of
hypoglycemia remains, it is generally not an obstacle to racing well. In
fact, Williams & Chryssanthopoulos (1997) have noted that most transiently
hypoglycemic athletes are unaware of their hypoglycemia -- i.e., a brief
drop on blood sugar at the start of exercise does not make them feel tired
or light-headed.
As a side note, the reason for caffeine's effectiveness was
originally thought to involve the release of fatty acids into the
bloodstream. However, caffeine has been shown to improve treadmill running
even in doses that don't raise blood fatty acid levels (Graham & Spriet,
Journal of Applied Physiology 78: 867-74, 1995), so we still aren't sure
exactly why it works. It should also be remembered that caffeine
is a diuretic; thus, those who use it should take care to keep themselves
well-hydrated.
During the race
The athlete's main nutritional goals during a long workout or race
are to keep his/her body supplied with fluids and carbohydrates. For
these things to be useful to the body, they must pass from the stomach to
the small intestine and then be absorbed across the intestinal wall into
the bloodstream. Therefore, it makes sense to consume fuels that move
quickly from the stomach into the intestine and then are rapidly absorbed
by the blood.
According to a recent review (Maughan & Leiper, Canadian Journal
of Applied Physiology 24: 173-87, 1999), concentrated energy drinks do
not meet these criteria; they are slow to reach the intestine and slow
to deliver water to the blood once they get there. Studies disagree on
whether dilute sports drinks such as Gatorade get to the intestine as fast
as pure water; once in the intestine, however, the water in Gatorade seems to be
absorbed faster than pure water (Gisolfi et al., American Journal of
Physiology 258: G216-22, 1990; Ryan et al., Journal of Applied Physiology
84: 1581-8, 1998). Thus, considering the process as a whole,
Gatorade-like beverages are probably about as effective as pure water in keeping
the body hydrated, and they offer the additional advantage of supplying
carbohydrates and electrolytes.
If sipping Gatorade mid-race is beneficial to performance, how
about chowing down on gels or PowerBars? As Owen Anderson states in the
most recent issue (volume 16, number 4) of Running Research News, one
can benefit from eating gel or similar foods, but one must drink
the right amount of water along with the gel to make sure that the
resulting mixture is neither too concentrated nor too dilute. "Take in too
much water, and you end up with a hypotonic sports drink in your gullet
which delivers too few carbs to your leg muscles. Take in too little
water, and you concoct a syrupy goo within your intestines which actually
drags in water from surrounding tissues and spurs diarrhea," he explains.
"It's far easier to simply use sports drink thoughout the race."
Another practical issue concerns the end of your race or workout.
Let's say you only have 20 minutes of exercise to go; is it worth tanking
up on fluids one last time? The data of Maughan et al. (Experimental
Physiology 75: 419-21, 1990) show that, like water, Gatorade-like
beverages begin to enter the blood within a few minutes of being drunk.
The take-home message here is that marathoners should think twice before
skipping an aid station at mile 24.
After the race
The primary goals of post-race nutrition are to replenish the
body's supply of water, electrolytes (primarily sodium), and
carbohydrates. In addressing the issue of post-race hydration, we can
again ask whether Gatorade and similar drinks recharge the body more
effectively than water, and again the answer is yes. When large amounts
of pure water are imbibed, one's bodily fluids become very dilute, and the
body reacts by releasing much of the just-ingested water as urine. The
sodium and potassium in sports drinks replace what is lost in sweat, thus
restoring the body's supply of these ions and allowing it to "hang on" to
the water that is consumed simultaneously (Nose et al., Journal of Applied
Physiology 65: 325-31, 1988; Shirreffs & Maughan, Exercise and Sport
Sciences Reviews 28: 27-32, 2000).
While the articles just cited focus on what to drink after
exercise, the same ideas can be applied to pre-race hydration as well.
In other words, drinking an electrolyte solution rather than pure water
before a race will help insure that, at the start of the race, most of
this fluid will still be in your body rather than in your toilet. It's
also worth noting that, although ions are important for fluid retention,
you don't have to get them in liquid form. As Maughan et al. (European
Journal of Applied Physiology 73: 317-25, 1996) have pointed out, eating
sodium-containing food and washing it down with pure water rehydrates
the body just as well as drinking Gatorade. (Once you're done running,
achieving the perfect ratio of food to water is no longer quite so
critical.)
In summary, race-day nutrition is a bit more complicated than
Coach Behr made it out to be. Nevertheless, with a careful look at the
scientific literature and some careful planning, you can make your
next race -- and the one after that -- a bit easier.
One of my reasons for writing this column is to expose readers to a
resource they might not otherwise be aware of, namely, the vast body of
scientific literature on exercise. This stuff can be frighteningly
technical and is therefore usually read only by scientists; however, it is
also generally more accurate and more thorough than what you find
elsewhere. Thus, if you care deeply about training and/or nutrition, I
would encourage you to read this literature yourself -- perhaps with the
help of a scientifically-minded friend, if science isn't your
thing.
Assuming that you want to peruse the Journal of Applied Physiology
and other such page-turners, where should you go? Your best bet is a
university medical library such as the U.W. health sciences
library, which houses a superb collection of exercise-related journals.
This library is open to the public, has a user-friendly layout, and is
staffed by courteous, knowledgeable people.
Those who prefer to obtain their information via the web may wish
to check out PubMed.
PubMed is a comprehensive and easy-to-use searchable database of biomedical
research articles. For example, if you wanted to obtain a listing of papers
authored by G. J. Crowther in 1997, you would simply type "Crowther GJ
1997." PubMed also provides links to the websites of individual journals,
some of which allow you to download their articles free of
charge.