This is incredibly reductive. There have been several studies which have demonstrated that even with the same calorie intake and exercise levels, western adults

This is incredibly reductive. There have been several studies which have demonstrated that even with the same calorie intake and exercise levels, western adults still weigh more than their ancestors a few generations ago. It's unclear why, but there are a number of factors which may be involved, e.g. PFAs, increased stress/decreased sleep, changes in gut microbiomes, etc.