2Heeldrive - Walk it off Wimp!

Have you ever been warned to avoid eating carbohydrates the hour before exercise? If so, you’re not alone. This is one of the most prevalent notions among athletes. But is it myth or is it fact?

It turns out the source of the finger pointing is research published almost 30 years ago. In the study, researchers had 8 students fast overnight. In the morning the students were given either water, 75 grams of glucose in water, or a liquid meal containing protein, fat, and carbs. Thirty minutes later they were asked to cycle to exhaustion at 80% of VO2 max. The students repeated the same regimen later while exercising at 100% of VO2 max.

The investigators found pre-exercise feeding produced no differences in the cycling times to exhaustion during the all-out sprint, but endurance time was reduced following carb feeding prior to the 80% of VO2 max regimen. The researchers also noted that after both the glucose and the liquid meal feedings, most of the students exhibited a temporary decrease in blood glucose at the onset of exercise. Glucose returned to normal and remained normal, even at the time of exhaustion. However, the investigators surmised that taking in carbs just prior to exercise must increase the rate at which carbs are used as fuel during exercise. They attributed the reduction in endurance to an accelerated use of muscle glycogen, even though muscle glycogen was never determined in the study.

At the time, this was big news. This study was one of the first published on the subject. In droves endurance athletes began avoiding carbs just before exercise.

The funny thing is, virtually every study published since has failed to confirm the findings of this original investigation. In fact, in a review of 11 studies on pre-exercise carbohydrate feedings, the original study was the only one to find a reduction in endurance following the ingestion of carbs in the hour before exercise. None of the subsequent studies found that endurance was hampered and some even showed a benefit. In those that showed improvement in endurance, the benefit ranged from 7 to 20%. That’s no small benefit!

Some thirty years later it is now clear that the temporary lowering of blood glucose that occurs after consuming carbs is a normal metabolic response. And while a few individuals may develop an exaggerated lowering of blood sugar in response to carbs in the hour before exercise, in the vast majority of athletes this decline in blood glucose is quickly self-corrected when exercise begins. Moreover, it has no detrimental effect on endurance performance.

So, for most athletes, carbs in the hour before exercise do not need to be avoided. In fact, carbs at this time may be helpful for the very same reasons they’re helpful during your pre-exercise meal, 2 to 4 hours before you train or compete – to replenish your muscle and liver glycogen stores. This is especially the case after an overnight fast when liver glycogen stores are likely to be depleted, if you’ve not fully recovered from a prior training session, or if a full meal isn’t a realistic option prior to exercise.

Finally, as you put carbs-in-the-hour-before-exercise back on the table for consideration, keep in mind that it is always a good idea to test your pre-exercise fueling regimen during training. Make sure whatever regimen you follow on the day of an event is well tested beforehand.