Recently, an IDC candidate asked me if the fizz from a carbonated drink consumed prior to a dive could increase nitrogen bubbles and the chances of decompression illness. The answer is, “No.”
With the exception of a very small number of nitrogenated beers, mostly European, the bubbles in effervescent drinks, including all such sodas and waters, are composed of carbon dioxide (CO2), not nitrogen (N2). And of course it is the latter that’s the gaseous culprit in DCS in recreational divers.
Moreover, gas bubbles cannot enter the circulatory system from the GI system under anything resembling normal circumstances. It is theoretically possible that bubbles could enter blood circulation secondary to gastric or intestinal breach. However, it would be an extraordinary situation where expanding beverage bubbles would cross a GI wall rather than be expelled from one or the other end of the alimentary tract either by normal transit, flatulence or belching.
Small amounts of gas from swallowed CO2 or N2 bubbles could pass into venous circulation in a dissolved state. However, when this occurred the gas would be rapidly dispersed in the blood coursing to the heart and off-gassed through the lungs without issue.
As for other possible contributions to DCI, the caffeine common in carbonated cola drinks does mildly increase the excretion of urine, but this is only in amounts much greater than contained in a can or bottle of normally caffeinated soda. Given sensible consumption, caffeine’s contribution to dehydration, and therefore possibly to DCS, is negligible. As for the sugars in sweetened fizzy drinks, these may promote obesity, diabetes, and tooth decay, but in anything remotely resembling sensible quantities make no meaningful contribution to dehydration.
DocVikingo has been scuba certified for more than 35 years and has dived all over the world. He is a practising doctor in the Baltimore/Washington, D.C. area and has held faculty positions at several major hospitals, including Johns Hopkins. With an interest in diving medicine, he serves as administrator at Scuba Clinic Online.