Carbs of different stripes provide fuel to go, go, go
Athletes are urged to consume carbohydrates frequently -- before they start activity, during exercise to “keep the tank full” and as soon as possible after a workout to replenish carbohydrate stores. But it wasn’t always so. Only 100 years ago, it was widely believed that beef was the cornerstone of an athlete’s diet.
Then, in 1920, came the first published study demonstrating the importance of a high-carbohydrate diet to fuel activity. And in 1923, researchers studying Boston Marathon runners first made the connection between low blood sugar and fatigue.
Since that time, the ideal composition of carbohydrate-rich sports products has become a hot topic of research. Several recent studies have examined the physiological effects of different dietary sugars during exercise -- fueling the development of sports-related food products containing these “functional carbohydrates.”
A high-carb diet helps to stockpile glucose -- stored as glycogen in muscle and liver -- so it’s ready to be used when needed. Such a diet is one of the best defenses against early fatigue during physical exertion. Because glucose is the sugar we need, you’d think -- logically -- that a high-glucose diet would be the best one for an athlete.
But glucose isn’t present in foods to any great extent. It appears, instead, as carbohydrate-rich foods are broken down during digestion. Breads, pasta, cereals, fruits and dairy are all rich sources of carbohydrates, which is why they’re typical fare for athletes. Digestion also produces other simple sugars such as fruit-derived fructose, galactose from milk, trehalose from honey and maltose from starches.
These naturally-occurring sugars may have some beneficial effects beyond just providing much-needed carbohydrate.
One study, published in the European Journal of Applied Physiology in 2003, compared the effects of three sugar solutions (glucose, galactose and trehalose) on performance and blood sugar levels in eight well-trained male cyclists. The beverages were consumed just before an exercise bout of 20 minutes of low-intensity cycling followed by a timed trial of all-out effort.
Performance was comparable with all three sugars, but blood glucose levels rose and fell more gently with trehalose and galactose. In other words, rather than being the favored pre-exercise carb source, glucose is less favorable, triggering a stronger release of insulin to bring blood sugar down. The authors point out that if activity begins when insulin levels are high, blood sugar levels might drop too low, causing early exhaustion.
Other studies have shown that carbohydrates are more efficiently used as fuel when several sugar sources are consumed at once, and various mixtures have been studied in an attempt to find the best blend. One study of cyclists, published in 2005 in the journal Medicine and Science in Sports and Exercise, compared beverages prepared with a mixture of fructose and maltodextrin (a short chain of glucose molecules) with maltodextrin alone. The total carbohydrate was the same in each group, but the fructose-maltodextrin combo increased the rate of energy production from the drinks by 40%. This improved “fuel efficiency” from food helps preserve the body’s own carb stores.
Strenuous exercise not only drains carbohydrate reserves; the metabolic activity required to sustain it leads to production of cell-damaging free radicals. This can lead to fatigue. A small placebo-controlled study published in May in the journal Nutrition demonstrated that an extract produced from unripe apples helped to counteract fatigue in athletes after a series of bouts on an exercise bike. Apples, like all fruits, are a good source of carbohydrates. But the researchers concluded that procyanidin, an antioxidant in apples, was responsible.
On the heels of this burgeoning research, consumers are now faced with a dizzying array of designer products in the form of fortified waters, sports drinks and energy drinks, some of which may tout proprietary blends of carbohydrates, electrolytes and antioxidants.
In the melee, whole foods may be getting short shrift. These, after all, are more than just carbohydrates or antioxidants -- they are complex mixtures containing phytonutrients, vitamins, minerals, protein, fats and fluid. So while designer sports foods and beverages have their place in the athlete’s diet, many standard staples have merit.
At this year’s American College of Sports Medicine meeting in New Orleans, researchers from the University of Texas at Austin reported that a bowl of wheat flakes with milk was just as effective in boosting exercise recovery as a specially formulated sports drink -- by providing a good balance of glycogen-restoring carbohydrates as well as protein for muscle repair. Another tried-and-true recovery drink for many athletes is chocolate milk -- it’s protein- and carb-rich, with fluid, potassium and cocoa antioxidants to boot.
A healthful diet with adequate carbs and fluids is critical for peak athletic performance. But even if you’re only a weekend warrior, experimenting with different foods and incorporating a few specialized sports products might just help you achieve your best.
Susan Bowerman is a registered dietitian and assistant director of the UCLA Center for Human Nutrition.
