"I am training for my second attempt at the Ford Lake Placid Iron Man in 2008. In race nutrition is what prevented me from finishing it in 2007 - I overloaded my body with calories in too short a timeframe.
I weigh more now than I did training for this years race and wondered if a Vegan diet might help me get the nutrition I need while helping me lose weight. Thought?"
First of all, congrats for taking on an IM! I hope your second attempt is all you want it to be. I have a two part answer to your question about using a vegan diet to lose some weight. It is possible to use a nutrient dense plant-based diet to lose weight while simultaneously fueling your body with the nutrients it needs while training. That said, the key is eating nutrient dense food. Losing weight is ultimately a matter of taking in fewer calories than you're burning, and just because food is vegan doesn't mean it'll make you lose weight. It's possible to eat a "junk food" vegan diet, which won't help you. The advantages of using a plant-based diet to lose weight is that if you're eating primarily whole grains, legumes, and fresh fruits and veggies, you're easily going to meet your body's needs for balanced sources of protein and carbohydrate, and (if you're preparing your foods without lots of added fats) lower your fat intake. As CPB has pointed out on this blog before, the healthy high carb intake is great for endurance training. Another advantage is that the high fiber intake will help you feel full.
Some of the best books on the subject, in my opinion, are Dr. Joel Fuhrmann's Eat to Live*, Dr. Colin T. Campbell's The China Study, professional IM triathlete Brendan Brazier's The Thrive Diet, and Davis & Melina's Becoming Vegan (there's a helpful chapter for Vegan Athletes).
Best of luck! Keep in touch and let us know how it goes!
*A note about Eat to Live: While I recommend Furhmann's explanation of how a plant-based diet is healthy for your body, I would not recommend following his 6-week plan to the letter while training. He's anti-snack, first of all, and I think snacks are crucial when you're in training mode. As far as I can tell, it's the only way to get in enough calories. His general principles, however, strike me as sound, and he provides some great recipes.