Barrettscv 

Most cyclist don't ride long enough or hard enough to have a nutritional issue. However, any ride longer than three hours should include continuous intake of between 150 and 300 calories per hour. Like many cyclist, I can burn 500 calories per hour, but I can't digest 500 calories per hour. Even if I were to eat a 500 calories serving and eat every hour, I'll run a calorie deficit. Since it's unusual for me ride more than 4 hours continuously, I almost never run out of fuel, because my body has several hours of reserves it will draw from.

However, when I'm running a long-term and intentional caloric deficit with the goal of weight loss, I'll make every effort to eat 250 calories per hour while on the bike. I'll also have a complete meal before and after a 3 or 4 hour ride. This not only helps me avoid depleting my meager reserves, it helps me to avoid grazing on low quality calories.

I'd follow these rules if I were a full time vegetarian. I'm currently a near-vegetarian when I'm eating at home, but I allow meat in my diet when I travel on business.