How many teaspoons of baking soda can you eat at one time without fear of overdosing?

Difficult to answer: Generally shouldn't take baking soda. It is an old remedy for heartburn, reflux, dyspepsia, ulcers, gerd and the like. A rare use of a teaspoon of baking soda in a glass of water would be considered safe by an adult but not with any frequency. There are better remedies. Depending on other illnesses, there is too much salt (soda) to be taking this (chf, kidney dz). Don't! see pcp.