I've always found these medieval fantasy to be pretty funny, assuming the grains and vegetables we have with limited technology and knowledge could be close to what we have in the modern world. It took few generations for optimised strain of grains to spread through the continents. It took a while for our bananas to have no seeds. Bananas consumed by natives in countries producing bananas still have seeds. Tomatoes are not as large as they are now. Without adequate transport and trade, it's unlikely that nutrition rich vegetables could have made it to the market. Meat should be difficult to come by too.