Don't get fooled by this alkalize your body bs. It's not based on science and lacks the understanding of basic human physiology.
You can't alkalize the whole body per se. Each part of your body has different pH range that is necessary for its proper function. Stomach is one example.
That's not to say we shouldn't care at all what we eat but all you can basically do is to help your body to maintain those different pH ranges more easily by making healthier food choices.
But like said, don't confuse that with alkalizing or whatever the term is.