Use clean backgrounds. The background textures and color you choose have the ability to drastically affect the overall appeal of the website. Lots of texture and graphics in the background can be distracting. If you are going to use a color on the background, you should make sure there is significant contrast between the background color and the text. Be careful when using brighter and darker colors such as red or yellow. They cause visual fatigue (temporary loss of strength and energy resulting from hard physical or mental work) and the reader will lose their focus on the text.
I find it interesting that you talked about nutrition supplements for athletes. I am very close to launching such a product for enhancing aerobic exercise performance in women (ie. improved times in a 3 mile run).. The product contains no stimulants or exotic herbs. In fact three of the five ingredients are well known minerals, but in forms not found in most multi-vitamin-mineral supplements. The research behind the product comes from me. The credibility behind the research is that I am a professor of human nutrition with over 100 research papers. Now, the trick will be to use my connections and credibility in a business savvy way.