Effects of dietary nitrate on oxygen cost during exercise
Article first published online: 17 JUL 2007
Volume 191, Issue 1, pages 59–66, September 2007
How to Cite
Larsen, F. J., Weitzberg, E., Lundberg, J. O. and Ekblom, B. (2007), Effects of dietary nitrate on oxygen cost during exercise. Acta Physiologica, 191: 59–66. doi: 10.1111/j.1748-1716.2007.01713.x
- Issue published online: 17 JUL 2007
- Article first published online: 17 JUL 2007
- Received 9 March 2007, revision requested 17 March 2007, final revision received 29 March 2007, accepted 29 March 2007
- electron transport;
- energy expenditure;
- nitric oxide;
- uncoupling protein;
Aim: Nitric oxide (NO), synthesized from l-arginine by NO synthases, plays a role in adaptation to physical exercise by modulating blood flow, muscular contraction and glucose uptake and in the control of cellular respiration. Recent studies show that NO can be formed in vivo also from the reduction of inorganic nitrate (NO3−) and nitrite (NO2−). The diet constitutes a major source of nitrate, and vegetables are particularly rich in this anion. The aim of this study was to investigate if dietary nitrate had any effect on metabolic and circulatory parameters during exercise.
Method: In a randomized double-blind placebo-controlled crossover study, we tested the effect of dietary nitrate on physiological and metabolic parameters during exercise. Nine healthy young well-trained men performed submaximal and maximal work tests on a cycle ergometer after two separate 3-day periods of dietary supplementation with sodium nitrate (0.1 mmol kg−1 day−1) or an equal amount of sodium chloride (placebo).
Results: The oxygen cost at submaximal exercise was reduced after nitrate supplementation compared with placebo. On an average Vo2 decreased from 2.98 ± 0.57 during CON to 2.82 ± 0.58 L min−1 during NIT (P < 0.02) over the four lowest submaximal work rates. Gross efficiency increased from 19.7 ± 1.6 during CON to 21.1 ± 1.3% during NIT (P < 0.01) over the four lowest work rates. There was no difference in heart rate, lactate [Hla], ventilation (VE), VE/Vo2 or respiratory exchange ratio between nitrate and placebo during any of the submaximal work rates.
Conclusion: We conclude that dietary nitrate supplementation, in an amount achievable through a diet rich in vegetables, results in a lower oxygen demand during submaximal work. This highly surprising effect occurred without an accompanying increase in lactate concentration, indicating that the energy production had become more efficient. The mechanism of action needs to be clarified but a likely first step is the in vivo reduction of dietary nitrate into bioactive nitrogen oxides including nitrite and NO.