I've kept a food diary for two years now; I have information on what I have eaten every single day since day 1. Not only has it come in handy to monitor how my body and mind respond to what I put into my mouth, it has also become extremely valuable in diagnosing my gluten intolerance and other health matters. When my doctor or nutritionist has had a concern about my health, I can turn to a page in my food diary that relates to that period of time and usually pinpoint exactly what went into my body which caused my body or mind such stress. It's also been really helpful resource for myself; meal plans and recipes are logged there and even my exercise/training routine. If I want, for example, to get back to how good I felt in October 2007, I can turn to those pages in my diary and see what was working.
Two components that I am now diarizing are how much water I put into my system, making 5 square boxes on a page and checking one off when I have a litre of water. I am also recording hours of sleep. Not surprisingly, when I have caffeine after 11am, I sleep less at night. My book is a small journal with blank pages- pages where I can record the date myself, in case I need more than one page a day for thoughts/recipes/meal planning. I tried a daytimer, but felt restricted by the one-page-a-day outline.
I will carry my journal everywhere, to remind myself that if I put something in my mouth, I have to admit it and put it in my journal. Keeps me accountable and I'm glad for the information it has provided me so far. How many of you are keeping health logs/diaries? Try it, even for a day and see how you feel looking back on your day after recording it. Then try it the next day as well. It may help in unexpected ways, next time you have a health concern.