But that hasn't been working for the average American, right?

Aging is rough.

And the high calorie to nutrient ratio in this country makes it really hard to avoid adding pounds.

This country is calorie and diet obsessed, and yet average weight seems to keep increasing.

Ask anyone who has been obese and subsequently lost weight and they'll tell you the same thing. Eating less is both a sufficient and necessary condition to losing weight. Exercise is neither sufficient nor necessary because the caloric surplus these people are on significantly exceeds the amount that you can practically burn through exercise. While you're right that exercise can help on the margin, it's just not a useful intervention that moves the needle much as far as weight loss goes.

Only assuming you have a steady body weight and diet, which is a very bad assumption for most overweight and obese people.

Not to mention, the processes in your body are way more complex than all this makes them out to be. For moderate exercise, after an adaptation period of a few weeks to months, there is almost no calorie impact from the exercise itself on your total calorie expenditure: your metabolism adjusts and various internal processes are deprioritized to prioritize the exercise.

This is in fact a major component of why exercise is so healthy: it doesn't do much for weight loss, but it stops/slows down all sorts of unnecessary processes in the body that are actively harming your overall health.

Not true, on two counts:

- one, your body may crave more food because of the energy loss - the Lipostat model suggests that your body has a target weight (well, fat level, more precisley), and will adjust hunger up if calory expenditure goes up

- your internal processes use way more energy than you can consume through exercise in a modern lifestyle (2000+ calories a day just from sitting still, for many adult males), and there is a lot of room for the body to adjust those up and down to make up for the extra exercise to keep up your current weight. So if you consume 2000 Cal a day with 0 Cal from exercise, with moderate exercise you will end up conauming 1600 Cal a day from internal processes + 400 Cal a day from exercise after some time (a one time run will absolutely consume extra, if your run every day, you'll get less and less extra Cal from your runs, until you reach about net 0, assuming you're not increasing the amount of exercise constantly).

30 mins of running = 5km marathon.

Most people can walk 30 mins but I would doubt if most can run a marathon.