I narrate a national car show called Steel Dreams. Although I have recently wrapped this project, I did notice something great about it towards the end of it; The effect of weight loss on my voice.
When I started the project a year ago, I weighed 252 lbs. Not that bad for someone who is 6'6", but not great either. Technically, I was overweight by nearly 30 lbs. About 10 weeks ago, I decided to get into shape. Since then I have lost 25 lbs. The affect on my voice has been very positive.
I thought about it for a while and I think the main reason might be stamina. In the course of getting in shape, I've developed better "wind". (don't be crude, you know what I mean) Basically, my lungs are stronger and I can take deeper breaths. Additionally, my circulation and blood pressure are waaaaay better, giving me more staying power at the mic. I would also like to add that my stress level has dropped tremendously over the course of these 10 weeks and perhaps this is the greatest contribution getting in shape has on your voice. Lower stress always sounds better in the final product.
So, if you are looking for a way to make your performances "up a level", I suggest you start with your body. Hope this inspires someone to get healthy.