No additional food production needed, but instead a change to eating lower on the food chain.  The best diet for health and athletics is based on plants.  Below is a good discussion
of the benefits and myths involved:

http://www.nealhendrickson.com/mcdougall/030900puathletesarepeopletoo.htm

And speaking specifically to cycling, carbohydrates are what is needed for endurance.  The differences in fatigue time is astounding - comparing a meaty diet Vs. a complex carb one (this is well references in a great book called "With the Grain" by a female author named Brown.  Unfortunately it is OOP and I'm not sure where the references are, and I'm too lazy to find them :)  Regardless, the link above applies to cycling too.

One of my office colleagues is a bicycle racer. His team just got the silver in some national track event, so he's no slouch. He's been on a vegan diet for maybe five years or so.

This looks like a reasonable first cut on efficiency:

http://constructal.blogspot.com/2006/03/whats-mileage-on-that-bicycle.html

Jim