Demand for grains is actually quite elastic. When the price of things like corn and wheat is low, farmers feed them to animals and people consume more meat. When the price increases, people consume less meat and more grain, and in doing so, consume a lot less grain.

In economies where people are too poor to afford meat, fluctuating food prices are a much bigger issue. But in the US, we use more food than we need to in order to enjoy a luxury commodity.