On the site of the Daily Telegraph, Amy Iggulden writes an article headlined, "In diet-mad Britain the serious reader is left on the shelf." She points out that ten years ago, Stephen Hawking's "A Brief History of Time" was on top of the best-seller charts, whereas now it's diet books and TV spin-offs. These include "You Are What You Eat," by "nutritionist" Gillian McKeith (her credentials are questionable), and Jamie Oliver's cookbook, as well as hypnotist Paul McKenna's book promising to change your life in seven days.
Of course, nobody knows how many people who bought Hawking's book ever actually read it, and diet and self-help books have been big a long time. But the charts' domination by TV tie-ins and celebrity authors (or at least celebrities who put their names on books, even if they are ghost-written) has definitely accelerated. The autobiographies of show business types and sports people are also an ever-growing segment of book sales, and must be destined to grow even further since many of these people are writing their first volumes while still in their 20's.
In fiction, the trend has moved away from the comfortable romance novels of Catherine Cookson to gruesome crime novels and global thrillers.
It's always useful to understand what people are buying but you can't let it sway you--you have to write what you really believe in. And now I have to get back to writing my next book: The Serial Killer's Guide to Easy Weight Loss and Instant Riches.