I talked to researcher Samantha Farmakis this afternoon about her work on obesity and, yes, some interesting things already seem to pop out. As measured by trends in BMI since 1990 Australians are getting fatter -- no ambiguity about that (there is elsewhere in the literature!) except for some bizarre trends at older ages. There are questions about the appropriateness of BMI calibrations of obesity that we need to note and it would be nicer to have a longer time series. New data is arriving soon this year.
One point was that exercise levels have not fallen so this does not seem to be the rationale for us getting fatter. It might be that overall activity levels have fallen even if exercise levels have not so we need to sort out this data. Indirect data suggests people drive further to work so perhaps they walk less. We need to be careful about the definition of 'exercise'.
Food prices do seem to have fallen though not, on inspection in areas where we might expect weight problems to arise -- sweets, confectionary and fast food prices seem to have galloped away.
Data on smoking and alcohol consumption exists. Both have fallen off a bit recently.
Income levels have risen but as food is a normal necessity this seems an implausible explanation of sharply rising obesity.
Data on female work force participation would seem to be useful though dominated by trends that have declined.
Anything else? I am a bit of a fatty myself so I want to know.
Update: An interesting review by Andrew Leigh is here.