Your food expenditures vary with the amount of work you do, no different than your car's fuel expenditures. They are most certainly not a sunk cost for this purpose.
Actually not so much surprisingly - the key exceptions being if you are working in very cold climates where the body has to generate more heat to keep you alive or you're training competitively for very physically sports.
It turns out that about 70-80℅ of what most people consume goes into simply keeping them alive (research basal metabolic rate & daily calorific requirement) and the impact of "work you do" is only a small variation - with the above exceptions.
Also interestingly (unable to search the paper reference on phone) there is research that shows that dramatically different lifestyles like Namib desert nomadic hunter-gatherer vs. typical urban don't actually differ on metabolic rates (accounting for non-fat weight)
What is the claim you're making? Assume 80% of Example Man's diet is his rest energy requirement. The other 20% goes toward discretionary things like moving. This means that if Example Man doubles his discretionary activity, his food consumption will increase by 20% rather than 100%.
It does not mean that if walking three miles takes one apple worth of energy, Example Man actually only needs to consume 0.2 apples in order to walk an extra three miles. He needs to eat the full one apple. This article doesn't consider food as a percentage of your diet at all; it considers food as the cost of moving. Your point isn't relevant.
You should have posted that at the top level, so this could be the top comment. While the statistics are nice to look at, I have read the article you mentioned, too (was on HN a while ago) and instantly thought that metabolism unfortunately renders the whole calculation useless and wrong.
> While the statistics are nice to look at, I have read the article you mentioned, too (was on HN a while ago) and instantly thought that metabolism unfortunately renders the whole calculation useless and wrong.
Why did you think this? Can you articulate a change that metabolism would make to the calculation?
It adapts, like my parent comment has said. Most of our energy is spend on keeping the system running, not running with our feet. If we start to run, we burn more energy, because our metabolism has not adapted yet, once it adapts (see his example with Africa), there is very little change. Obviously this is simplified.
But the argument could be made that the average American runs a calorie surplus so some percentage of the food/fuel cost could be deducted, for Americans, at least, no?
I guess the issue is surplus relative to what - recommended daily calorie intake vs. the calories required to maintain excess weight. My point was the former, yours seems to be the latter.
Well, I started off by saying "no, food expenditures are not a sunk cost, they are directly related to the amount of work you do". The idea here is that doing x extra work leads to eating x' extra food, where x' is some constant multiple of x (and "food" is measured in energy).
Your response, as far as I can see, says that because Americans already run a caloric surplus, x extra work should only lead to x' - k extra food intake, where the missing k energy is made up by the existing caloric surplus. I responded then and respond again now that this perspective makes no sense; the extra work is an ongoing expenditure and must be exactly balanced by an ongoing intake. For the supposed caloric surplus to be offset against the extra work of extra walking, the person would need to be experiencing constant weight gain beforehand. Nobody[1] is.
You may think that Americans weigh too much, but that's irrelevant; a change in weight is a nearly-pure one-time effect with no influence on dietary requirements. They are eating exactly the amount they already use for the activities they already do.
Am I missing something about your point?
[1] Actually, people with Prader-Willi syndrome will eat if it is possible to eat, no matter how full they are. They will experience constant weight gain if not subject to external control. But they have a serious genetic defect.
It turns out that about 70-80℅ of what most people consume goes into simply keeping them alive (research basal metabolic rate & daily calorific requirement) and the impact of "work you do" is only a small variation - with the above exceptions.
Also interestingly (unable to search the paper reference on phone) there is research that shows that dramatically different lifestyles like Namib desert nomadic hunter-gatherer vs. typical urban don't actually differ on metabolic rates (accounting for non-fat weight)