I read this book sometime back as part of my journey of understanding food and how it affects the body and mind. In the last two years I have managed to lose about 10kgs of weight and in the process have learnt a fair deal about food, although not enough to talk authoritatively with a nutritionist.
Roger Wilson's book deals mainly about how the author lost a significant amount of weight himself after trying his own diet plan. The diet he followed was eating fruits and proteins. His lack of fundamental knowledge of nutrition makes his commentary a suspect from the very beginning. This book is more a chronicle of the authors weight loss journey than a guide to healthy eating.
Conclusion: Better to avoid.