> Why? Because it's much more likely that they're one of the <nearly everyone> who can't estimate calories in/out well than that they're an outlier with a sign

> Why? Because it's much more likely that they're one of the <nearly everyone> who can't estimate calories in/out well than that they're an outlier with a significant metabolic drop in some small number of years, especially given that small misestimations are large enough to yield the observed behavior. Maybe there's something else going on, but "without more details" it wouldn't be the first place I'd look. > older people needing different diet Absolutely! I hope nobody took away opposing statements to that from what I said. The double whammy of needing fewer calories and being less equipped to absorb vitamins and whatnot necessitates a significant change in diet with age. I was only commenting on this one person's experience aging just a few years in the middle of their life. > walking > That is not how this works tho. Especially for walking, that's exactly how it works. Walking builds negligible muscle mass, and everything else you've mentioned (aside from perhaps impacts on hunger), adds up to well under a 5% error in calorie estimates -- well under the noise floor from applying a general purpose calorie estimate to any one specific person.