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An alkaline diet is basically based on greens, but not all veggies are actually alkaline. We found a very good Alkaline Food Chart, though. Now he drinks soya milk instead of the usual milk, and he avoids meat. He also drinks lemon water instead of just plain water, and he has switched to stevia as his sweetener.
He also quit tobacco and drinking besides diet modification. Now, it has been over a week, and he says he feels healthier. His heartburn stopped and he doesn´t feel much pain in his stomach anymore.
I knew that some people switch to alkaline diet to prevent cancer, but I think this diet works for hyperacidity too. We´ll see whether alkaline diet really works in a few more weeks, I guess, and I´m actually considering switching to it too.