Many years ago, I happened to look through the definition of good health by the World Health Organization:"..a sense of physical, mental, and social well-being...." it said. I hope it remains the same today. I think its a very good guiding principal for leading one's life.
A lot of fads and fiction has grown around the "Healthy Living" industry eg this thing about avoiding wheat because of the way it is grown. There is no scientific fact to support this.
I believe in moderation. I am not a fan of any passing trend, past or present, and I am in fairly good health. I have modified my diet according to scientific facts as they became available, and currently this would be a combination of the macrobiotic and the paleo diets. In between I drink plenty of clean water. I avoid fizzy drinks and alcohol only very occasionally.
And last, but not the least, keep active: so excercise in any form. Even lifting your arm 3 times is considered as beneficial, to doing nothing at all.