The researchers were surprised that activity inequality was largely driven by differences between men and women.
In countries like Japan – with low obesity and low inequality – men and women exercised to similar degrees.
But in countries with high inequality, like the US and Saudi Arabia, it was women spending less time being active.
Jure Leskovec, also part of the research team, said: “When activity inequality is greatest, women’s activity is reduced much more dramatically than men’s activity, and thus the negative connections to obesity can affect women more greatly.”
The Stanford team say the findings help explain global patterns of obesity and give new ideas for tackling it.
For example, they rated 69 US cities for how easy they were to get about on foot.
The smartphone data showed that cities like New York and San Francisco were pedestrian friendly and had “high walkability”.
Whereas you really need a car to get around “low walkability” cities including Houston and Memphis.
Unsurprisingly, people walked more in places where it was easier to walk.
The researchers say this could help design town and cities that promote greater physical activity.