Where Did the Other Calorie Go?

I heard an ad promoting sugar the other day, presumably the work of some sugar trade group, possibly The Sugar Association, Inc. (see below). In this spot, sugar was described as having only 15 calories per teaspoon. I found this very interesting because sugar used to be described as having 16 calories per teaspoon. (I knew I couldn’t be wrong about this because, during summer vacations in college, I worked for American Sugar Company and developed a stronger than average interest in facts about sugar.) I wonder what happened to the other calorie? Has sugar changed? Has the teaspoon gotten smaller?

A search of the Web was helpful, even though it didn’t really answer my question. The Sugar Association, Inc., Web site prominently displays a banner with the 15 calories per teaspoon claim, but most sources (e.g., Lawrence Hall of Science at U.C., Berkeley) give 16 as the proper number. Curiously, one source, Detroit Medical Center of Wayne State University, cites a calorie count of 35 calories per teaspoon!

Given The Sugar Association’s vested interest in making sugar into a health food, I suspect that 16 calories per teaspoon is the proper figure. I do wonder what the rationale is for 15 (or 35, for that matter). I’ll try to crack this mystery when I get the chance.