Questions about history, science and Orthodox Christianity.

For starters, bear with me because I'm 16 and I'm trying to understand Orthodoxy. I have only just started reading my bible but I have been Orthodox my whole life.

So recently, I have been doing lots of research on human diets in history/science, and Christianity. I don't seem to understand how timelines or facts can work at all. For starters, human diets according to the bible vs science don't make sense. People say our (far back) ancestors didn't eat grains, but the bible talks about bread very early on. I also don't understand how fruits were genetically modified to be the way they are, but Adam and Eve ate them.

What diet does the Bible recommend we follow? Even if it doesn't give the foods we can and can't eat, what are the foods and eating habits we should do and not do?

Those are just two examples, but my main question is: do history and Orthodox Christianity just not align at all? The things that they claim to have happened in history just don't align with a 6000 year old earth.