You're right that a lot of people eat more than they should, and exercise less than they should. We aren't efficient in this regard. Yet when a human exercises

You're right that a lot of people eat more than they should, and exercise less than they should. We aren't efficient in this regard. Yet when a human exercises, they breathe more, and produce more CO2. There is an internal carbon cycle that must be maintained. If any person exercises more without changing their diet, their rate of 'carbon accumulation' (to be kind) will decrease. For someone like myself who isn't in the habit of accumulating carbon - a long-term impact of riding to work will be that I will lose weight [0]. As a carbon-based life form, if I don't change this to be non-negative, I'm clearly down a path of self-destruction, and will need to increase my food intake eventually. [0] - https://pdfs.semanticscholar.org/f407/588843385c964c7de0bc9e680499c806c734.pdf https://pdfs.semanticscholar.org/f407/588843385c964c7de0bc9e...