It is well accepted and supported that taking in carbs during endurance training or competitions will enable an athlete to perform at a higher intensity for a longer period of time. But, there is some confusion as to how many carbs to recommend during exercise.
Out with the old
Conventional wisdom has long held that well-trained athletes should consume no more than 60 grams of carbs per hour during exercise. This is based on the idea that the maximum rate at which ingested carbs can be absorbed from the digestive tract and metabolized as fuel by working muscles is about 1 gram per minute or 60 grams over the course of an hour.
In with the new
However, new research from Dr. Asker Jeukendrup, of the Human Performance Laboratory, School of Sport and Exercise Sciences, University of Birmingham, United Kingdom, has toppled the conventional wisdom. A recent study published in the February 2008 issue of Medicine and Science in Sport and Exercise, the official journal of the American College of Sports Medicine, shows that consuming a specific blend of glucose and fructose carbohydrates improved endurance performance by an average of eight percent in trained athletes compared to consuming the same amount of glucose alone. It turns out that the 60-grams-of-carbs-per-hour convention was based on research where only a single carbohydrate source, glucose, was given to athletes. These studies were accurate in showing that glucose alone can't be absorbed any faster than about 60 grams per hour. But Jeukendrup and his team fed a combination of glucose and fructose in a 2:1 ratio to endurance athletes. And instead of topping out at 1 gram of ingested carbs per minute, the athletes were able to absorb and metabolize about 50% more ingested carbs every minute during exercise.
This finding is astounding if you're an athlete faced with tough competition where minutes or seconds off their time to finish can mean a medal or elimination. Instead of consuming 60 grams of carbs per hour, you can now consume 90 grams of carbs every hour as long as those carbs are in a 2:1 ratio of glucose to fructose. To make that easy and convenient for you, PowerBar Performance Bars, PowerBar Energize Fruit Smoothies, PowerBar Gels, PowerBar Gel Blasts and PowerBar Endurance Sports Drink all feature C2 MAX, the exact 2:1 blend of glucose and fructose that was the subject of Dr Jeukendrup's groundbreaking research.
How does the unique carb combination work?
Jeukendrup and his research colleagues believe that the glucose-fructose combination works better than glucose alone because having multiple carbohydrate sources allows more carbohydrate to be absorbed from the digestive tract. The thinking is that glucose and fructose have their own separate transport systems in the digestive tract. These transporters help carry ingested glucose and fructose from the digestive tract into cells. However, the glucose transporter can only carry glucose, and like a train, once it's filled, the doors close and it can't carry anymore. But the revelation is that fructose has its own separate transporter or train. So even though the glucose train is filled to capacity, the fructose train can deliver even more fuel to working muscles. Thus, by providing both glucose and fructose, and taking advantage of both transport systems, you too can deliver more fuel to your muscles and extend endurance even further.
In research just published, Jeukendrup proved the endurance advantage. He gave trained cyclists either plain water, plain water plus glucose, or plain water plus glucose and fructose in a 2:1 ratio. The cyclists rode for two hours and then had to complete a time trial of about one hour's duration. In turned out that when the athletes ingested the combination of glucose and fructose, they achieved a time trial performance that was 8% faster than when they consumed glucose by itself. And average performance time was 19% faster when the carb combination was compared with water alone.
Easier on the Gut too
If that isn't not enough good news, research is also showing that this same combination of carbohydrates are better tolerated during exercise, than glucose based products. This is good news for athletes that have trouble tolerating carbohydrates during exercise.
Drinks containing carbohydrates that use different transporters for intestinal absorption seem to result in a smaller amount of carbohydrate remaining in the intestine and therefore osmotic shifts and malabsorption may be reduced. This probably means that drinks with multiple transportable carbohydrates are less likely to cause gastro-intestinal distress. Interestingly, this is a consistent finding in studies that have attempted to register gastro-intestinal discomfort during exercise carbohydrate 8-15. Subjects tended to feel less bloated with the glucose+fructose drinks versus glucose drinks. The tolerance of carbohydrate drinks and development of GI distress seems highly individual and therefore strategies for carbohydrate intake will always have to be developed on an individual basis.
Carbohydrate and fluid delivery
We often advise to avoid the intake of highly concentrated carbohydrate solutions because these solutions have been shown to delay gastric emptying and fluid absorption. Although there is a lot of evidence to support this there are also observations that impairment of fluid delivery is minimized when combinations of multiple transportable carbohydrate are ingested. Fluid delivery with a glucose+fructose solution has been shown to be greater than fluid delivery from a glucose solution.
Bottom line: When it comes to counseling endurance athletes on Carbohydrtaes during exercise, go with the cutting edge. To optimize performance recommend consumption of a 2:1 ratio of glucose to fructose during exercise, with doses up to 90 grams per hour of this powerful carb fuel mix. Finally, remember that PowerBar C2 MAX gives you that cutting edge endurance advantage.