Wednesday, February 10, 2010
For anyone who has spent any time around a gym or even around fervent gym goers, you have probably heard the adage that chocolate milk is the ideal drink of choice post exercise to aid in recovery. In fact, dairy companies have put out commercials advertising the purported athletic benefits of drinking chocolate milk post exercise. I must admit that I personally love a 500ml carton of chocolate milk after my workouts. But is there any evidence to support all the hype?
Now, before I go any further, I want to warn our readers that the evidence I am about to discuss may not pertain to many people who do a leisurely 20 minute jog as their workout. If your goal is weight loss, rather than recovery from intense exercise and thus improved performance on subsequent exercise bouts, then drinking 500ml of chocolate milk (330 kcals) may not be appropriate. Indeed, some obesity experts liken chocolate milk to a liquid chocolate bar – as in, something that should be seen as a treat and thus consumed in minute quantities.
Endurance exercise performance (cycling, running for long distances) depends highly on the amount of glycogen (stored sugar) in the muscle, and intense endurance exercise can quickly deplete these muscle glycogen stores. Thus, it is important to replenish these stores between bouts of exercise to ensure good performance in the subsequent session. However, there is an important window of time after an exercise session during which your body will replenish your glycogen stores – within 30-60 mins post exercise. If you wait over 2 hours to eat or drink something rich in carbohydrate, your levels of muscle glycogen may be half of that if you had the same meal within 30-60 mins of exercise. As this has stuck with me ever since my undergraduate course on sports nutrition, I try my best to time my workouts so that they occur directly before a meal.
With regards to the composition of what you ingest post intense endurance exercise, it is currently recommended that 50-75g of carbohydrates along with some protein (in quantity of 1/4 to 1/2 the grams of carbohydrates, or approximately 15-30g) are ingested soon after intense exercise. Interestingly, one 500 ml serving of 1% chocolate milk includes 55g of carbohydrates and 16g of protein – thus seemingly being designed ideally for post-exercise recovery.
While research directly testing the ability of chocolate milk to help with exercise recovery is a bit scant, I found one good example. In this study, published back in 2006, Karp and colleagues tested 9 trained cyclists by having them perform an interval workout followed by 4 h of recovery, and a subsequent endurance trial to exhaustion at 70% intensity, on three separate days. On each of the 3 days, the subjects received a different drink – a fluid replacement drink (basically water with 30g of carbs - Gatorade) , a specially designed post-exercise carbohydrate replacement drink (~70 g of carbs, 18g of protein, and 1.5 g of fat), and chocolate milk (70g carbs, 18g protein, and 5.0 g of fat) . In contrast to consumption of the fluid replacement drink (basically Gatorade), the ingestion of either chocolate milk or the carbohydrate replacement drink resulted in 50% increase in endurance performance in the test to exhaustion. Thus, it turns out that chocolate milk is better than Gatorade and just as good as specially designed exercise recovery concoctions for helping athletes recover from intense exercise and improve subsequent performance. Keep in mind that chocolate milk is also cheaper than special exercise recovery drinks.
Again, I must emphasize that unless you are exercising strenuously for extended periods of time, and you could care less about your time to exhaustion on your next exercise bout, or if you are exercising for weight loss purposes, chocolate milk may not be the ideal choice. In this situation, as your carbohydrate stores are less likely to be depleted, a nice glass of water will suffice.
Karp JR, Johnston JD, Tecklenburg S, Mickleborough TD, Fly AD, & Stager JM (2006). Chocolate milk as a post-exercise recovery aid. International journal of sport nutrition and exercise metabolism, 16 (1), 78-91 PMID: 16676705
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