How is it that calorie free drinks contain citric acid?

Question

I'm a bit confused as I took biochemistry last semester. Doesn't citric acid enter the krebs cycle and get metabolized which leads to NAD getting reduced. So how is it that zero calorie drinks like Diet Coke can have citric acid in them?

Answer 1

You are in fact correct.  Citric acid can enter the Krebs cycle and produce ATP.  However, soft drink companies only consider carbohydrates when they count calories.  And in fact, carbs are not the only molecules that can produce calories.  So the label is incorrect, but the soft drink companies don't want to get bogged down in technicalities.  And since citric acid produces very little ATP on its own, well, you see where this is going...