Nitrate may boost endurance, but data is ‘very low- to moderate-quality,’ says meta analysis
Nitrate is one of the dietary ingredients endorsed by World Athletics as being generally regarded as boosting performance. The others are caffeine, creatine, B-alanine and bicarbonate. To test whether recent research supports the hypothesis that nitrate boosts endurance, a team associated with several Canadian academic institutions conducted a literature search on several databases, including the Cochrane Central Register of Controlled Trials. They imposed no language restrictions on their search.
Their approach of what endpoints to look for had the unique input of a trained elite athlete. Co-author Reid Coolsaet, an alumnus of the University of Guelph who is a world-class track athlete, marathoner and sports coach. Coolsaet has represented Canada at the Summer Olympics.
Based in part on Coolsaet’s input, the research team decided to focus on trials that had endpoints of power output, time to exhaustion, and VO2, among others as metrics of athletic performance.
The initial literature search cast a wide net, finding more than 22,000 studies that met the initial criteria, which included using beetroot juice, nitrate tablet/capsule/beetroot crystals, non-beet foods (pomegranate extract, watercress, red radish) and other (dissolved betaine, high nitrate diet, nitrate-rich gels, sodium nitrate dissolved in water).
Quality of available studies varied widely
After paring the initial search results down, the researchers sorted through 449 studies to arrive at their final data set, which amounted to 73 studies. Even with this rigorous sorting of the wheat from the chaff, the researchers said the final data set still suffered from an unfortunate degree of heterogeneity.
In all of the measures for which the authors found a positive benefit from nitrate supplementation (power output, time to exhaustion, distance traveled and VO2) the authors cited “serious risk of bias,” “serious publication bias,” “serious imprecision,” and “serious imprecision” as limiting factors.
Nevertheless, the researchers said, “This systematic review and meta-analysis suggests that dietary nitrate supplementation improves performance during endurance sports. This is especially evident when evaluating important outcomes, such as power output, time to exhaustion and distance traveled. However, given its mixed effects on explanatory variables, like blood lactate and VO2, further research is needed to determine the specific means by which nitrate supplementation impacts physical endurance.”
Coolsaet: Beetroot juice may have helped but GI upset was too much
A separate commentary from Coolsaet detailed his experience using beetroot juice in his competitions. Coolsaet said he performed to expectations in competitions in which he adopted that supplementation strategy, but that he ultimately chose to cease using the substance.
“My protocol was to drink at least 500 ml of beetroot juice approximately 2–3 h before a competition or run. The competitions all went well as I met or exceeded expectations. Of course, it’s impossible to credit beetroot supplementation alone as there are many variables that lead to successful competitions. I did experience GI distress, which was not problematic in the 10 km distance, slightly problematic competing in the half marathon distance, and problematic over the marathon distance. It was the GI distress that led me to stop supplementing with beetroot juice,” Coolsaet said.
Source: Journal of the International Society of Sports Nutrition
8, Article number: 55 (2021)
The effects of dietary nitrate supplementation on endurance exercise performance and cardiorespiratory measures in healthy adults: a systematic review and meta-analysis
Authors: Gao C, et al.
