The best speeches are when you can relate to your audience.. What has living a healthier life done for you? How has it improved your life? What have you been able to do now that you couldn't do before?
^^ Yes I have alot to relate to for the topic, Im just looking for ideas, I have the credibility part I am having a bit of problems finding articles for the topic.
I agree with Mal. I'm sure you can talk for a long time about what you have done. You can start with what/why you started your journey. Talk about how you did it. That can be broken down into diet and exercise. Talk about what changes you have gone through. Wrap it all up with some motivation and how others can get started.
I was invited back to the hospital exercise program i started with to tell my story and my speach lasts about 45-50 mintues. I always find it easier to present my own material instead of what somewhat else has written. Good luck!!