I do not. I have been in field for so long that I am quite conscious of my food and fluid intake. However, I agree with Karin, for a client who needs to learn how to accurately assess nutritional habits, especially if weight loss is a goal in her/his training program, keeping a detailed food journal is essential. The critical factor is you as the trainer are qualified and capable of evaluating the journal.
I don’t personally keep a food journal because my personal goals are not food related, but many of my clients do. It’s a fact that a person who tracks their diet in writing is more conscious of the foods they eat and, therefore, more apt to avoid or at least recognize poor choices.
One of my favorite sites / apps for a food tracker = myfitnesspal.com