From Flex, July '04 ... what it actually translates to at the end of the day is probably negligible, of course depending on amounts and coingestion/timing ...
Originally Posted by joedonj
Q | Are carbonated beverages good for bodybuilders?
A | Carbonated beverages are often viewed as digestive aids because the gas from the carbonation causes distension of the stomach and intestines. This distension is sensed by the gastrointestinal (GI) system and causes an increase in motility--meaning the food that's in the stomach passes through the GI tract at a faster rate. This may be good for decreasing indigestion but bad for enhancing digestion and absorption of nutrients--particularly amino acids from protein.
Carbonation may interfere with absorption because the higher acidity of such beverages inhibits normal secretion of stomach enzymes, such as proteases, which break down protein into amino acids. Carbonated beverages also may somehow force much of the food consumed to sit in the higher part of the stomach, where the enzymes are not found, preventing the normal breakdown of protein.
If food moves more rapidly through the stomach, there is less time for enzymes to do their work. Also, if fewer enzymes are doing their work, some of the protein you've eaten may not get properly digested.
Another problem with drinking a carbonated beverage during a meal is that you may feel less satiated afterward. This was discovered in a study of patients with indigestion and constipation. Carbonated water taken with meals reduced the study subjects' indigestion and constipation, but they were less satiated than when they drank plain water with food.