Thursday, October 24, 2013

Beet Juice for Milers

By Alex Hutchinson

Over the past few years, I've written a lot about the potential endurance-boosting effects of beet juice. Unlike the vast majority of supposed performance-enhancers, the claims are actually backed by some pretty solid evidence. But there has been one discordant note: in the few studies that have looked at truly elite athletes (like this one, published earlier this year, on elite cyclists), the effect seems to disappear. In some sense, this isn't surprising: the bodies of elite athletes are already highly optimized, so it's very hard to see any improvement in any parameter, no matter what intervention you apply. Still, it raises an important question for elite athletes considering using beet juice: is the effect real but too small to see in studies, or is it non-existent?
At the Canadian Society for Exercise Physiology conference last weekend, there were a couple of additions to this debate. One was a presentation by Kyle Boorsma from the University of Guelph, looking at the effects of beet juice on 10 elite 1,500-meter runners. How elite were they? Well, they had an average VO2max of 79 ml/kg/min. As far as I can remember, this is the highest group average for VO2max that I've ever seen in a study by a big margin; in the cycling study I linked to above, the average VO2max was 72. The average 1,500 time was 3:55 +/- 8 s (Boorsma himself, currently a grad student, has a best time of 3:39). The basic finding of the results: beet juice didn't help the runners.
Specifically, they used a double-blinded crossover design, so each runner did two eight-day protocols with either concentrated beet juice shots or a placebo (which was also concentrated beet juice, but with the nitrate removed). They took three shots on the first day, 2.5 hours before running a 1,500 solo time trial; then they took two shots a day for the next six days; then they took three shots again on the eighth day and then did another time-trial. Neither the acute nor the chronic supplementation made any difference in the time-trial results. They also performed running economy tests at three different submaximal speeds on a treadmill on the first and last days of the protocol, and again there was no difference between beet juice and placebo.
I asked Boorsma why he thought elite athletes don't seem to benefit. Here's part of his reply:
There are many  possible mechanisms (improved blood flow, mitochondrial respiration, Ca2+ handling, contractility, etc.) by which NO3- [nitrate] supplementation is proposed to improve economy and performance in recreationally active [people].  It's likely that adaptations following endurance training have already optimized these mechanisms. For example, increased capillary density following endurance training many provide trained individuals optimal blood flow such that NO3- supplementation cannot enhance blood and O2 delivery in these individuals.
So is this the final word on beet juice for elites? Not necessarily. One thing to consider is individual variability: despite the average results, two of the athletes in Boorsma's group seemed to be "responders" who, for whatever reason, saw improvements when they took the beet juice.
Another speaker at the CSEP conference happened to be Andy Jones himself, the University of Exeter researcher most associated with beet juice as an athletic supplement. His talk was a fairly general overview of the beet juice research, focusing on health as well as performance implications. Toward the end of the talk, he did address the question of whether truly elite athletes can benefit. Like Boorsma, he listed various adaptations conferred by extensive endurance training (such as the fact that elite athletes tend to already have higher baseline plasma nitrite levels and better muscle oxygenation), which might leave less room for beet juice to provide a boost. He also noted some research from New Zealand in which elite rowers benefited from beet juice -- perhaps a consequence of the greater full-body muscle recruitment required in rowing compared to sports like cycling and running? Similarly, an Australian study published just a few weeks ago found that a "moderate" dose of beet juice (one shot of concentrated juice) had no effect on highly trained rowers, but a "high" dose (two shots) did improve performance.
The bottom line? The picture is a bit murkier than previously thought for elite athletes; for the rest of us, on the other hand, getting plenty of nitrates still seems like a good idea.

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