A friend of mine recently asked me “Is regular soda or diet soda better for you?” I tried to probe for details.  “Are you talking about calories?  Obviously, if you’re watching your weight or restricting carbohydrates, you should have the diet soda.” “No, I don’t mean the calories.” “Oh, you mean the concern that the citric acid might leach calcium out of your body?” “No.  I just mean overall, are they good or bad for you?” This precipitated an important revelation that had been percolating...