We are what we eat
A friend of mine had a good theory for how he approached his nutrition. It was a three step approach. The first step was easy:
Eat anything you want
It was the second two steps that would take a bit of work:
Then tune in to how you feel afterwards.
And ask yourself why you chose to eat it.
The premise of the whole approach was very straight forward. On some level we know what is right for us and what is not so good for us. If only we listened to our bodies, then we would start to build up an intuitive approach to how to eat healthily.
It is often commented that animals also have an innate ability to tune in to what they need to eat. For livestock and horses, we can go a step or two further and provide a selection of potentially appropriate plants so that they can self select when they need to. The tricky bit is knowing the selection that is needed in the first place to cover all the bases.
With ruminants there is now a very elegant system that allows farmers to observe the subtle clues that livestock give when their diet needs tweaking.