The caustic soda is then exposed to the power plant's exhaust, where it combines with carbon dioxide to create, over two steps, sodium carbonate and then sodium bicarbonate.
For starters, the participants' sodium consumption was gauged by measuring the sodium content of their urine over just one 24-hour period at the beginning of the study.
The membrane started out very leaky, but over time, the membranes would have slowly closed, preventing much larger sodium particles from leaving the cell while smaller protons could still slip through.
Although this method is considered the gold standard for estimating sodium intake, that lone urine test may not provide an accurate snapshot of the participants' everyday intake over the full eight-year study, as the researchers themselves note.