Different fuels create different amounts of CO2 per joule though. This is not just a truism in combating climate change but also a key tool when observing metab

Different fuels create different amounts of CO2 per joule though. This is not just a truism in combating climate change but also a key tool when observing metabolism. Whenever someone gives numbers for how much of some exercise energy consumption is from fats and how much is from carbs it is determined by measuring CO2 output and comparing that to measured energy output.