I understand the vitamin B2 in Marmite/Vegemite aids the flow of carbs into the muscles so is a great supplement to take for strenuous execise. It is water soluble and the body doesnt retain it, so it must be taken immediately before the execise.

I had to buy some Vegemite last month then the supermarket was out of Marmite - it spread easier but only tasted like imitation Marmite.