Doubts emerge over carbohydrate-protein energy drinks

Numerous studies have shown that carbohydrate energy drinks can enhance performance in and recovery from endurance exercise. However a new breed of energy drink for use during exercise has recently appeared on the market. Known as ‘carbohydrate-protein energy drinks’ they have a very similar composition to conventional carbohydrate energy drinks, but instead of supplying 100% of their calories as carbohydrate, they comprise of around 80% carbohydrate and 20% protein (usually as whey protein).

According to the manufacturers, these protein-containing carbohydrate drinks offer several advantages over conventional carbohydrate-only drinks for endurance athletes, including enhanced endurance performance, better recovery and less muscle damage. However, there’s some uncertainty about the precise performance benefits because up until now, no study has demonstrated that additional protein ingested during exercise actually reduces the time to cover a fixed distance – ie makes endurance athletes faster in a race situation. What several studies have demonstrated is a dramatic (13-36%) improvement in endurance capacity – time to exhaustion – when protein is ingested during exercise.

The argument goes, therefore, that if your goal is to keep going for as long as possible at a fixed pace then ingesting protein along with carbohydrate during exercise is advisable. On the other hand, if going faster is your goal then there’s no evidence that adding protein to carbohydrate is worthwhile. One counter to this argument is that for long-distance events, maintaining a steady pace for longer is exactly what’s needed. Moreover, no study to date has ever shown that taking a carbohydrate-protein drink actually reduces performance under race conditions.

However, research just published by scientists at the University of Bath looks set to deepen the argument. The study compared the effects of energy-matched carbohydrate-only and carbohydrate-protein drinks on cycling time-trial performance. Twelve competitive male cyclists and triathletes each completed two double-blind trials separated by 5-10 days; in each trial, the subjects performed a 45-minute variable-intensity exercise protocol on a stationary bike while drinking either a 9% carbohydrate-only solution or a mixture of 6.8% carbohydrate plus 2.2% protein. Importantly, each cyclist consumed exactly the same number of calories (5.2kcals per kilo of body mass) on both occasions for both drinks. The subjects were then asked to cycle 6km in the shortest time possible – ie to simulate a time-trial race.

The key finding was that the average time to complete the 6km time-trial was 433 seconds when drinking pure carbohydrate and 438 seconds when drinking carbohydrate plus protein – a significant performance drop of 0.94% with the inclusion of protein. The researchers concluded that ‘reducing the quantity of CHO included in a supplement and replacing it with protein may not represent an effective nutritional strategy when the supplement is ingested during exercise’.
Int J Sport Nutr Exerc Metab. 2010 Feb;20(1):34-43