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Many people wrongly believe that they should avoid sugars and other simple carbohydrates before exercise as these might trigger a surge of insulin and hypoglycaemia (low blood sugar). In fact, pre-exercise carbohydrate can help you to maintain higher blood sugar levels, delay fatigue, improve endurance and therefore help you to train harder for longer.
In an experiment at Cornell University, triathletes who ate 2-3 bananas immediately before a cycle trial were able to keep going 16-18 minutes longer than those who ate nothing. When researchers at Ohio State University gave cyclists a carbohydrate (sugar) drink one hour before a time trial, performance times improved by 12V2% compared with those who drank a placebo. A study of sedentary men carried out in 1995 at the University of Massachusetts found that eating a confectionery bar before exercise did not adversely affect performance or result in hypoglycaemia. Far from triggering a surge of insulin, exercise actually suppresses it by stimulating the production of adrenaline and other hormones which reduce insulin production, allowing blood sugar levels to be maintained longer. This is certainly an advantage: muscle glycogen may be spared, fatigue delayed and performance improved.
In practice, have approximately 50 g carbohydrate 5-30 minutes before you exercise, although you should leave at least two hours after your last meal. Experiment with different amounts of carbohydrate at different time intervals before exercise to find the strategy that suits you best.
Suitable pre- or post-exercise snacks supplying 50 g carbohydrate
1. 2-3 Bananas
2. 1 pint isotonic sports drink
3. 3 oz dried fruit
4. Jam sandwich (2 slices bread with 2 tbsp jam)
5. 5 rice cakes with 1 banana
6. 2V2 oz breakfast cereal
7. 1 confectionery bar (50 g)
8. 250 ml glucose polymer drink (20% carbohydrate)
(N. B. Accompany solid foods with a large glass (150-300 ml) of water)