The book explains clearly how food combining is based on the premise "don't mix foods that fight". According to Dr Hay, the foods that fight are mainly concentrated proteins and starches. Our digestive system, says Dr Hay, is set up to deal quite separately with proteins and starches. When eaten together, neither is fully digested. Simply by keeping proteins and starches for separate meals, this book claims, you will feel the benefits of more complete digestion. After a few weeks, it also claims, this in turn leads to higher energy levels, and a "satisfied" body which rarely craves any particular food, because it is fully nourished.
Those who have a real interest in nutrition are likely to find that this book makes fascinating reading. However, with a large chunk of the book devoted to explaining the theory of the Hay Plan, and how it can help people with a variety of ailments, particularly any related to the digestive system, those who are not too interested in theory may find it a little dry. This said, it is easy enough to skip to "Part Two - the Hay System in Practice", where you are given plenty of advice about how to get started, an easy reference diagram to remind you which foods are compatible, and a whole section of recipes which comply with the Hay System's "rules".
Most people who try the Hay Plan, or Food Combining, are converted within a few weeks. For myself, my energy levels were higher than they had been for several years, after just 2 weeks of sticking pretty strictly to the "rules" given in this book - so I, too, am a devotee. The biggest barrier to sticking entirely to the Hay Plan for any real length of time, is the way in which our Western diet constantly presents us with protein/starch mixtures - for example, meat and potatoes, protein fillings in sandwiches, sweet starchy desserts after a mainly protein meal, and drinks (such as wine and coffee) as an integral part of a meal (the Hay plan recommends drinking plenty of pure water, but avoiding drinking anything within 1/2 hr either side of eating, as this dilutes the acid or alkaline medium of the digestive juices, hence restricting the efficiency of the digestive process).
Despite these difficulties, how many "diets" do you know which allow you to eat any food you want, so long as you partner it with the right companions? The enthusiasm, dedication and sense of humour of the two writers manage to turn what could be a rather dry account of the "do's and don'ts" of food combining into an absorbing read. It was written some time ago, so the recipe section is a little limited, and there are much better Food Combining recipe books available today. However, if you want a handy reference/handbook for the simple, original Dr Hay's theory of Food Combining, you could do much worse.
I'd recommend this book to anyone who wants to really take charge of their health and weight. A word of advice, however... do try to read the book fully, and really familiarise yourself with the concepts, the suggested way of "breaking yourself in" to this way of eating etc., before beginning on the Hay Plan. It will make it a much easier, gentler and more effective process. I leave the last word to the authors: "just try it for 2 weeks, then make up your own mind".