If you want to find out what your overweight employees are costing you in sick time, increased health care, etc. you can use his online calculator.
This was a low cost thing to add to the site but makes it very interesting for business owners. As he continues to add things that engage his audience, his book sales and consulting practice will continue to grow.
If you are considering writing a book, start with the website now. Build an audience. This way, when your book hits the shelves, you are adding cool features instead of writing your about page. You can visit Tom's ever growing site at http://www.healthybodyweight.com