Hypothesis: obesity epidemic has a causal link to the rise in carbon dioxide level.
There is a parallel in the shape of the curve in the last fifty years roughly. Since 1960, the carbon dioxide level has been climbing. This is not the only cause, but only an environment change which we pre-1960 models were not born into, hence we did not adapt to in childhood. This reduced oxygen transfer may have reduced our energy level, and therefore our desire to be active. Food gives us a short term boost in energy and the first few ATP from sugar are easy to obtain oxygen free.
CPAP machines are often recommended for heavy people at night, and that helps many a great deal. This would drive more oxygen into those people. I was once in a weight wise group, and everyone except me was on a CPAP machine of some kind.
What kind of test could be devised to act as a proof of concept test? How about deep breathing exercise, on the hour and half hour, or as needed, about five or ten deep breaths, aka forced oxygenation?