You are unique, your digestive system is unique, your food preferences are unique, your constitution, in combination with ethnic provenance and health history, is unique.
It's ok to critically read books on diet trends (paleo, ketogenic, vegan, vegetarian, flexitarian, ethnic), or on nutrition, in order to become informed on the state of our food and its profound influence on our wellbeing. But then you need to test these theories mindfully on your own body to understand what agrees with you and what doesn't, what aggravates certain conditions or alleviates them, what gives you energy, what regulates your weight, what helps you heal. The one exception I'll take is refined sugar. It's not good for anybody. Period.
We like to simplify and standardize, but imagine what would happen if some diet fundamentalist prescribed the same diet for all seven billion people on this planet? Digestive systems have adapted over hundreds and thousands of years to what is available geographically. Prescribe a vegetarian diet to an Inuit, or an Inuit diet to a Hindu - ok, these are extreme analogies - and they would likely become ill.
So, take all you read, all that people say, with a grain of salt - then see what really applies to your own condition and constitution. Although I had already cut out a lot of grain from my diet (and lost quite a bit of weight in the process) I am currently trying this gluten-free thing. I'm really not convinced this is necessary for me - we'll see, hoping to prove myself wrong. No diet applies to all - which one is the right one for you?