What do you think about the Hay diet?

My horseriding teacher suggested me to start a Hay diet to be more in shape and lose some weight at the same time. I started it and it went really well, it feels good and even if it is a bit difficult to know every food content, at the end I made it. I was loosing weight and felt better in general (digestion, etc..). Then someone told me that the Hay diet can be a bit dangerous because you can lose your hair, so and because I didn't have any dietitian support, I stopped it and gained some weight again. Now I'm starting again, I'm doing exercise again and I feel better by the week. But I'd like to know your expert opinion on the Hay diet, or what do you think. Is it healthy?
Personally, everytime I separate carbohidrates and proteins , I feel much better in general. I don't eat cow milk but oat, spelt or rice milk, and I try not to eat oranges, pineapple, yoghurt, tomatoes, strawberries , chocolate and cheese with anything else. I've got my Hay triangle of associations printed and on my fridge and I sort of follow it but I'd like to know much more about it through your opinions.