Or did they not really mean that they work together?
Apple cider vinegar creates the seemingly paradoxical effect of making the digestive system more alkaline, as the stomach sees the inrush of acid and reacts by stopping acid production.
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I use a European product called Crastan Effervescente (con succu limone), which tastes good as the name implies and gives you the sodium bicarbonate. There exist similar American products.
Stomach acid contains hydrochloric acid (HCl)
Baking soda reacts to stomach acid with the sodium combining with the chlorine in the acid to produce sodium chloride -- table salt.
Or did they not really mean that they work together?
Yeah. It's weird, but they do work together. You mix half a tsp of bicarbonate in 8 ozs of water then add two tablespoons of apple cider vinegar in that order, from my experience. It makes a not unpleasant drink which I take twice a day. It seems to have helped my general health since I started this regimen at age 65.
Baking Soda and Vinegar is a good way to clear a drain. If you take both at the same time you’ll likely rupture something due to the gasses generated.