I read "The China Study" in one sitting the very day it arrived from Amazon - it blew me away that much! The sheer scope of the research and references, and the clarity of the conclusion they point to, should be enough to turn anyone off animal foods for life.
This book is about as far from a fad diet as you can get - Campbell has spent over 40 years studying nutrition, and has been personally involved in many of the ground-breaking studies this book details (including, of course, the massive China study itself). Not only that, but he came from a background that predisposed him to seeing the typical "Western" diet as the pinnacle of sound nutrition - and yet has come to believe the complete opposite through years and years of research.
I have been a health-conscious vegetarian for nine years, so compared to most people you wouldn't expect my worldview to have been shaken up all that much by this book. However, although my vegetarian diet was based on all the information that was readily available - fruit and vegetables are good, saturated fat is bad, etc - this book still laid waste to some of the myths even I hadn't been able to see through, because there's so much propaganda out there regarding nutrition.
Most importantly, Campbell discredits once and for all the huge conspiracies that have been built around protein and dairy. Most people know vegetables are healthy, even if they don't eat enough of them, but hardly anyone is aware that protein isn't the miracle nutrient it's touted as being. Not only is it very hard to eat too little protein, but most people eat far too much. Similarly, dairy is still promoted as "healthy", especially low-fat dairy (of which I was an avid consumer, until I read this book). We're led to believe we need it for bone health, even though a survey of osteoporosis rates around the world suggests exactly the opposite conclusion. And, as a vegetarian, people were always telling me I needed to eat dairy in order to get a good dose of protein, even though (as Campbell's evidence conclusively shows) the main protein found in milk actually promotes cancer.
The same day I read this book, I became a vegan. Fortunately, my diet had already been a "fringe" diet for years (not that a healthy diet should ever be considered extremist), so I'd long since discovered the joys of vegetables, fruit, whole grains, and tofu. But now I'm more determined than ever to "convert" my boyfriend and family to the green pastures of veganism - and I'll start by giving them all this book for Christmas. If you care about someone, and don't want them to die of a premature heart attack or cancer, how could you not give them this book?
Unfortunately, as convincing as Campbell's conclusions are, there are probably many people out there who simply - for some very inexplicable reason - don't care enough about their health to follow his guidelines. It's always baffled me why people continue to take up smoking when they know it's about the worst thing they could do for their health. Similarly, a lot of people who see the animal-based Western diet as the default will probably see Campbell's recommendations as too hard to follow, and will continue to regard healthy eating as somehow abnormal. Despite the solidity of his conclusions, so many people have been indoctrinated with the idea that eating animal foods is necessary for a "balanced" diet that they will remain incredulous, even though the evidence against this idea is so strong. Campbell's exposure of the corruption behind the nutritional information we're given is admirable, though, and I sincerely hope people listen to him.