Hello Henry and welcome.
You ask a very big question... "How does one ever really know the truth". Indeed "we are sold on the green stuff". For me, the truth is in the results of my choices. I always considered myself healthy and still do, knowing there remains room for improvement.
Upon adding green smoothies and more raw foods to my daily routine I had profound improvements. I fall asleep easier, I don't get super tired in the early afternoon, I sleep less but feel more energetic throughout the day, I no longer have a creaky body upon waking in the morning, I've slimmed down 25+ pounds and I no longer get my regular sickness - colds, flu, etc... It's interesting to find out that even though I thought I was healthy - I was easily able to become healthier.
The truth is a individual reality and the only way to know what the truth is for you is to experience it.
If there is anything I can answer for you, just let me know.