I agree with your first paragraph - there are significant corrections to the rule of "calories in - calories out = weight gain". That doesn't mean it's not a good first order approximation (in my experience, within about 15% [1]). It also doesn't mean that fat people aren't eating too much. If you are 40lbs overweight, eat less. If you are not overweight but don't have a 6 pack, that's the time to start worrying about exactly what you are eating.
Also, you are correct - the straw man you are arguing against is wrong. It would be cost inefficient to eat 18 salads and 0 big macs.
Now, lets say you are obese. That means you are eating 6 big macs. If you are constrained by cost, you could reduce consumption to 5 big macs (saving the cost of 1 big mac), and you will eventually be merely overweight rather than obese. Or you could change your consumption from 6 big macs to 4 big macs + 1 big salad, and you will approach a healthy weight (and save money). If you want a visible 6 pack, you might even need to play around with the exact composition of your 2250 calories.
You are also ignoring the fact that it isn't very expensive to cook healthy food at home. Last night I cooked about 6 meals from rice, lentils and frozen vegetables. Total cost: about $5. 6 big macs costs about $18.
Also, as for exercise, the lowest earners have the most free time and they exercise the least (I won't even get into the vast majority of poor who don't work at all). They spend the most time watching television. The highest earners have the least free leisure time and spend the most time on exercise (and the least on TV). I'm not sure why having more leisure time would make it harder to get exercise or cook a healthy meal.
[1] My personal experience: I was obese as a teenager. I got myself down to a reasonably healthy weight simply by reducing intake during a 1 year period when I was living well below the poverty line (this was during college and due to some unusual choices I made). I was hungry as all fuck. My rate of weight loss was within 15% of what calorie counting predicted.
Also, you are correct - the straw man you are arguing against is wrong. It would be cost inefficient to eat 18 salads and 0 big macs.
Now, lets say you are obese. That means you are eating 6 big macs. If you are constrained by cost, you could reduce consumption to 5 big macs (saving the cost of 1 big mac), and you will eventually be merely overweight rather than obese. Or you could change your consumption from 6 big macs to 4 big macs + 1 big salad, and you will approach a healthy weight (and save money). If you want a visible 6 pack, you might even need to play around with the exact composition of your 2250 calories.
You are also ignoring the fact that it isn't very expensive to cook healthy food at home. Last night I cooked about 6 meals from rice, lentils and frozen vegetables. Total cost: about $5. 6 big macs costs about $18.
Also, as for exercise, the lowest earners have the most free time and they exercise the least (I won't even get into the vast majority of poor who don't work at all). They spend the most time watching television. The highest earners have the least free leisure time and spend the most time on exercise (and the least on TV). I'm not sure why having more leisure time would make it harder to get exercise or cook a healthy meal.
http://www.bls.gov/news.release/atus.t11.htm
[1] My personal experience: I was obese as a teenager. I got myself down to a reasonably healthy weight simply by reducing intake during a 1 year period when I was living well below the poverty line (this was during college and due to some unusual choices I made). I was hungry as all fuck. My rate of weight loss was within 15% of what calorie counting predicted.