Health & Fitness: Carbs vs protein

Most cyclists are aware of the need for a diet rich in carbohydrate to fuel longer rides. That’s because carbohydrate (stored as muscle glycogen) is your body’s preferred source of fuel during moderate to intense exercise.

Even a slight shortfall can lead to tired, leaden muscles and poorer performance. This also explains the rationale behind the use of carbohydrate drinks during longer rides and immediately after training What’s mystified some scientists, however, is that supplementing the diet of endurance athletes with whey protein as well as carbohydrate seems to produce additional performance benefits.

In theory, using whey as a supplement shouldn’t increase endurance performance because, while protein is essential to maintain muscle mass and aid muscle repair after strenuous exercise, it’s not regarded as premium muscle fuel for endurance exercise (unlike carbohydrate).

To investigate this phenomenon further, Australian scientists from the University of Victoria have been studying the effect on endurance adaptation in cyclists 
of supplementing 
whey protein.

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The science
In the study, six well-trained male cyclists and triathletes undertook two separate periods of dietary intervention:

Carbohydrate-only supplementation and carbohydrate plus whey protein supplementation. Each intervention was followed for 16  days, and in the last two days carbohydrate intake was further increased to mimic a ‘carb-loading’ phase before the main event.

Both interventions provided the subjects with the same number of total calories and total carbs. On completion of the intervention, the subjects performed a very demanding cycling task, consisting of cycling for 60 minutes at 70 per cent of maximum oxygen uptake (moderate intensity) followed by a time trial to exhaustion at 90 per cent of maximum oxygen uptake (very hard!).

After the trial, the subjects recovered for six hours, then samples of blood and muscle were taken to measure blood hormone levels and to determine muscle levels of a substance called ‘peroxisome proliferator-activated receptor gamma coactivator-1 alpha’ (PGC-1).

PGC-1 is a very important molecule because it provides information on how much endurance adaptation is taking place in the muscles – higher levels of PGC-1 show the muscles have adapted better to endurance training and the bigger the gains will be.

In a nutshell
Levels of muscle glycogen in the subjects at the end of each trial were the same regardless of dietary intervention. However, compared to the carbohydrate-only supplemented diet, the carbohydrate plus whey diet resulted in significantly higher levels of the hormone insulin and very importantly, significantly higher levels of PGC-1.

So what?
This was only a small study, so caution is needed before drawing absolute conclusions. However, insulin is a key hormone in recovery because it helps muscles absorb carbohydrate after exercise. Thus higher levels of insulin after the ‘carbohydrate plus whey’ diet indicate that the muscles were better primed for recovery.

Meanwhile, higher levels of PGC-1 produced by the carbohydrate plus whey diet indicate that the endurance adaptations in the muscles as a result of training were larger.

Put these two together and it’s possible to understand why extra whey protein in addition to that high-carbohydrate diet could result in bigger endurance gains than carbohydrate alone. More studies will be needed to confirm these findings but the initial 
evidence looks promising.
J Int Soc Sports Nutr. 2013 Feb 12;10(1):8

This article was first published in the March 7 issue of Cycling Weekly. You can also read our magazines on Zinio, download from the Apple store and also through Kindle Fire.