Why don't we know what to eat?

Don is having a crisis about what to eat. He reads on nutrition and fitness. There is just so much information and rarely does it seem to agree with each other. Or it changes month to month. The only thing he has found to eat that no one has criticized is leafy, green vegetables. And he said who wants to live on that? It's a funny thing - with all our knowledge we still can't agree on this simple thing - what and when and how to eat! Baba Hari Dass who grew up in India and lives in California once said that it's not good to think so much about food. Just eat the best food available that you can afford. And fast for 12 hours every day so body rests. Now, so much is available and it's perhaps not all meant to be eaten all the time. Who knows? Really? I just don't get why we don't know what to eat. Or maybe we do and it's only complex because there is too much variety.