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Supplementation of dietary nitrate — commonly found in beetroot juice — increases nitric oxide bioavailability and can enhance exercise performance. In new research, scientists from the University of Exeter Medical School and the U.S. National Institutes of Health investigated the distribution and metabolic fate of ingested nitrate at rest and during exercise with a focus on skeletal muscle. Their results suggest that dietary nitrate supplementation may provide a means of enhancing human muscular performance.
Kadach et al. show, for the first time, that skeletal muscle rapidly takes up dietary nitrate, the elevated muscle nitrate following dietary nitrate ingestion declines during exercise, and muscle nitrate dynamics are associated with enhanced torque production during maximal intermittent muscle contractions. Image credit: Ken Bennett, Wake Forest University.
While it is known that dietary nitrate enhances exercise, both boosting endurance and enhancing high-intensity exercise, researchers still have much to learn about why this effect occurs, and how our bodies convert dietary nitrate that we ingest into the nitric oxide that can be used by our cells.
To help close this gap, University of Exeter’s Professor Andy Jones and colleagues traced the distribution of ingested nitrate in the saliva, blood, muscle and urine of 10 healthy volunteers, who were then asked to perform maximal leg exercise.
They wanted to discover where in the body the dietary nitrate was active, to give clues on the mechanisms at work.
An hour after the nitrate was taken, participants were asked to perform 60 contractions of the quadriceps — the thigh muscle active while straightening the knee — at maximum intensity over five minutes on an exercise machine.
The authors found a significant increase in the nitrate levels in muscle.
During the exercises, they found this nitrate boost caused an increase in muscle force of 7%, compared to when the participants took a placebo.
“Our research has already provided a large body of evidence on the performance-enhancing properties of dietary nitrate, commonly found in beetroot juice,” Professor Jones said.
“Excitingly, this latest study provides the best evidence to date on the mechanisms behind why dietary nitrate improves human muscle performance.”
Previous studies had found an increase of nitrate in tissue and body fluid after ingesting labeled dietary nitrate.
By using the tracer in the new study, the researchers were able to accurately assess where nitrate is increased and active, and also shed new light on how the nitrate we consume is used to enhance exercise performance.
“This study provides the first direct evidence that muscle nitrate levels are important for exercise performance, presumably by acting as a source of nitric oxide,” said Dr. Barbora Piknova, a researcher with the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health.
“These results have significant implications not only for the exercise field, but possibly for other medical areas such as those targeting neuromuscular and metabolic diseases related to nitric oxide deficiency.”
The study appears in the journal Acta Physiologica.
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Stefan Kadach et al. 15N-labeled dietary nitrate supplementation increases human skeletal muscle nitrate concentration and improves muscle torque production. Acta Physiologica, published online January 6, 2023; doi: 10.1111/apha.13924
