Writing a book is an excellent, time-worn way to be unhealthy. I'm probably at my least healthy I've been over the last few years.
First of all, I've taken up smoking. What a wonderful example I'm setting. I'm now on my third pack. Smoking is a perfect break to long stretches of writing -- it takes a few minutes, it's relaxing, and is actually a pretty good time to walk and think. And get some fresh air (???). And it gives you lung cancer. (But remember, correlation isn't causation...most of the smoking studies are just epidemiological studies, not randomly controlled trials!)
Second, my sleep habits got completely screwed up over the last few months. I was regularly going to sleep from 5-7AM. I have black-out shades, so I'd be able to get seven or so hours of sleep. But it's totally disconcerting to wake up at noon (or later). You feel behind on the day, and by the time everyone else is winding down, you still have lots of work to do. Luckily, I broke out of that pattern a couple weeks ago. I dropped the caffeine for a day, worked out super hard, took some over-the-counter sleeping aids that night, set four alarm clocks, then immediately exercised when I woke up.
Third, I'm drinking way more caffeine than I should. I wonder if this was contributing to the sleep problems.
My eating has remained good, with a slightly higher incidence of dark chocolate rewards. Anyhow, things are coming along and there's light at the end of the tunnel. And trust me, if this were a diet book, it would have been out long ago.