Energy expenditure might be related to longevity. Eating more and exercising more (and the energy required to keep your core temperature up) might kill you faster, maybe through free radical production from metabolism.
As someone who only started to exercise in their mid thirties, the idea of living longer through not exercising is laughable. Even if it were true, I would rather live to 65 with an able body than to live to 90 not knowing what my body was capable of.
[1] https://www.cnn.com/2017/05/15/politics/donald-trump-exercis...
There's a theory that it's actually heartbeats. Most animals have about 1.5 billion heartbeats.
"The reason an elephant lives longer than a shrew is not because its heart beats longer. It's because its heart beats slower. So it takes a few more years for the elephant to complete his or her up to one and a half billion beats."
https://www.npr.org/2007/08/18/12877984/size-matters-the-hid...