All foods depend on "IF" they contain enough Alkaline Minerals to overcome the acids created in the digestive process.
So if the foods are picked too green , this will cause them to be acid forming, like for example: If you eat a Top Quality Apple , it will be Alkaline forming and taste sweet and make you feel good!!
"BUT" if you eat a green(unripe) apple which is of poor quality, it will be high in NPN and will cause you to become very acidic and have a stomach ache!!
A person needs to learn some "COMMON SENSE" , if you eat something and it makes you feel bad, you need to find out why, and stop eating that kind of food!!