Andrew Hamilton looks at optimum fueling strategies for a half marathon, and explains why one size doesn’t fit all MORE
You’ve just woken up on the morning of a 10-K race, it’s only an hour or so before it begins, and you’re hungry as hell – but you’re concerned that taking in food might hurt your performance. Should you avoid food altogether, simply sip some tea with sugar, or try to take in a bit of solid food, such as an easily digestible banana?
Runners participating in early morning races are often confronted with problems like that, but until now they haven’t known exactly what to do, because the effects of various pre-race foods on performance haven’t been clear. A long-time concern has been that high-carbohydrate food consumed about an hour before strenuous exercise could harm performance by producing ‘rebound hypoglycaemia’. In this form of hypoglycaemia, blood sugar levels shoot up after the carbohydrate snack, insulin levels then rise dramatically, and – in response to the heightened insulin – blood sugar concentrations drop precipitously in the early stages of exercise, supposedly increasing an athlete’s sense of fatigue. The alternatives – taking in nothing or ingesting foods containing fat and protein – aren’t especially attractive, since fasting has been linked with low performance levels and fatty, high-protein comestibles tend to linger in the gullet, increasing the risk of gastric discomfort.
Fortunately, scientists at Texas Christian University in the United States recently asked 10 experienced runners to complete four 10-K races on separate days after ingesting various forms of carbohydrate. One hour before the competitions, which were held under hot, steamy conditions (32 degrees, 65-per cent relative humidity), the runners consumed either 54 grams (216 calories) of pure glucose, the same quantity of high-fructose corn syrup, a glucose-sucrose mixture, or 54 grams of banana. In all cases, these sources of carbohydrate were mixed with .9 litres (29 ounces) of water. In a fifth and final situation, the runners ingested only .9 Iitres of H20 and no carbohydrate before the race.
As expected, the pure glucose and glucose-sucrose drinks tended to produce profound drops in blood sugar 15 minutes into the 1 OK, while blood sugar was more stable after water-placebo or banana consumption. However, blood sugar did RISE during the latter stages of all races which followed carbohydrate consumption, and the early fall in blood sugar didn’t have any harmful impact on performance; average 1 0-K times were constant at about 41:30-41:50 in all five cases.
So, the bottom line is that taking in a small quantity of carbohydrate an hour before a 1 OK probably won’t hurt your performance, even though some rebound hypoglycaemia is likely to occur. If you know that running the race on an empty stomach will be a bad thing for you, it’s OK to wolf down some carbohydrate an hour before your race.
In the Texas Christian study, eating nothing at all was just as good as carbo snacking, but that’s only because the race – a 1 OK lasting about 40 minutes – was pretty short. In competitions taking longer than an hour, internal carbohydrate stores can become depleted, so any pre-race carbohydrate eating tends to be helpful.
Although the runners in the Texas research were fine after their carbohydrate snacking, some runners are more sensitive to hypoglycaemia. Such individuals who do need to eat something can take in a bit of carbohydrate immediately before the race, rather than an hour before; the ensuing exercise will blunt their insulin response and prevent their blood sugar levels from ‘yo-yoing’ up and down. Another possibility is to wake up – and take breakfast – several hours before the race, as long as the early rising doesn’t leave you feeling too lethargic to compete. Fitting a two and one-half to three-hour gap between your breakfast and race should totally eliminate the possibility that hypoglycaemia will ruin your competitive effort.
(‘Effects of Pre-Race Foods on Glycaemic Reaction’ Medicine and Science in Sports and Exercise, Vol26(5), 1994)