Beetroot juice contains nitrate which has been found to reduce oxygen consumption in a number of different situations. We did studies on experienced freedivers to reveal if there were beneficial effects in 1) static and 2) dynamic apnea, see below.
In static apnea, the diver should breath-hold for the longest possible time during rest. We found that beetroot juice resulted in 11% longer apneic duration that placebo juice (the same juice but with nitrate removed). When divers did apneas with a fixed duration of 2 minutes, their arterial oxygen saturation was higher after beetroot juice ingestion, than after placebo. This shows that somehow oxygen consumption had decreased after beetroot ingestion. Read the full paper HERE.
In dynamic apnea, the diver aims to swim the longest possible horizontal distance on one breath using fins in a pool. We tested how much oxygen remained in the divers blood after a 75 m swim after ingestion of beetroot juice or placebo juice. Guess what! They managed to swim the same distance using less oxygen after beetroot juice ingestion. With beetroot juice, the arterial oxygen saturation was 86% while after placebo it was 79% (P<0.01). Read the full paper HERE.
We concluded from both these studies that ingestion of beetroot juice (and likely other vegetables containing much nitrate) can enhance performance in competitive apnea sports.