Beetroot

Does beetroot improve stamina????

Last year I ate beetroot everyday in, and knocked 15 minutes off my PB for a half marathon, some may say it was the 2 stone in weight that I lost, however it might have been the beetroot!!
So how much beetroot do I need to eat, it's zero points at fat club so I do eat it to fill myself up, I was going to start taking the capsules they contain 900mg of beetroot extract but I can't work out how much that equates to in weight of beetroot. I've even spoken to a scientist about this.
Worrying about beetroot is much more fun than worrying about running 26.2miles, and yes that .2 is the most important bit.