Nitrate
Overview	Dietary nitrate (NO3−) is a popular supplement that has been commonly investigated to assess any benefits for prolonged submaximal exercise69 and high-intensity, intermittent, short-duration efforts.70 71
Mechanism	Enhances nitric oxide (NO) bioavailability via the NO3−-nitrite-NO pathway, playing an important role in the modulation of skeletal muscle function72 Nitrate augments exercise performance via an enhanced function of type II muscle fibres73; a reduced ATP cost of muscle force production; an increased efficiency of mitochondrial respiration; an increased blood flow to the muscle; and a decrease in blood flow to VO2 heterogeneities.74
Protocol of use	High nitrate-containing foods include leafy green and root vegetables, including spinach, rocket salad, celery and beetroot. Acute performance benefits are generally seen within 2–3 hours following an NO3− bolus of 5–9 mmol (310–560 mg).75 Prolonged periods of NO3− intake (>3 days) also appear beneficial to performance70 76 and may be a positive strategy for highly trained athletes, where performance gains from NO3− supplementation appear harder to obtain.77
Performance impact	Supplementation has been associated with improvements of 4%–25% in exercise time to exhaustion and of 1%–3% in sport-specific TT performances lasting <40 min in duration.73 78 Supplementation is proposed to enhance type II muscle fibre function,73 resulting in the improvement (3%–5%) of high-intensity, intermittent, team-sport exercise of 12–40 min in duration.70 71 Evidence is equivocal for any benefit to exercise tasks lasting <12 min.76 79
Further considerations and potential side effects	The available evidence suggests there appear to be few side effects or limitations to nitrate supplementation. There may exist the potential for GI upset in susceptible athletes, and should therefore be thoroughly trialled in training. There appears to be an upper limit to the benefits of consumption (ie, no greater benefit from 16.8 mmol (1041 mg) vs 8.4 mmol (521 mg)).80 Performance gains appear harder to obtain in highly trained athletes.77