So all I’m saying it’s not just energy conservation. Human body is not a machine where input=output. Some of the food you eat is excreted unprocessed and your metabolism can just slow down. So if you’re just using 5% more energy per day your body can speed up digestion a bit and get more colaries out of the same food or it can slow down more during the night and you will get a better sleep. There’s a limit to it of course but your body will deal with 5% change without using it’s energy stores.