And that tells you that your simplistic view that obesity is due to a "difference in metabolism" can't be true
I'll leave simplistic views to you, thank you very much.
You're the one spouting single cause, "you people are eating too much - that's why you're fat" nonsense.
and if people who exercise stopped exercising for a few weeks, they'd balloon.
That's exactly what happens to many high-school/college sports stars once they hit regular employment and stop their regular exercise.
Not in a few weeks though, as it takes longer to lose ALL that muscle and replace it with fat, and cause it takes A LOT of fat for it to become noticeable as they are already "big".
Obesity occurs when you keep eating even though your caloric needs are met; the difference is stored as fat. Most commonly that happens because processed foods are so efficient at delivering calories that you have ingested excess calories before your body tells you to stop eating, and because simple carbs are absorbed too quickly to be utilized. And the way to fix that is to eat foods that deliver calories slower.
Back to single bullet theory are we? Simplistic much? Or not enough?
Eating less IS a solution but unless you're in a prison or a hospital or have a personal cook/dietician counting your calorie intake - it will only cause you to yo-yo up and down.
Average human can't measure accurately OR afford to match in/out calories to the letter.
So, they end up starving themselves then binging on food then trying to quickly starve-off and sweat-off those calories - which is impossible.
It takes 10 seconds to eat a candy bar and two hours of walking or more to burn it out.
Let's assume that one can measure calories with great precision. Only eat measured out and labeled food.
And let's take a 2000 calories BMR, with "little to no exercise" 1.2 activity factor included in there.
Now reduce that by not eating 100 grams of white bread (about 2-3 slices) each day to an intake of 1740.
That's a reduction of 1820 per week, or about a pound of fat lost every 2 weeks.
A single 14", 850 gram pizza on Sunday, as a "reward" for keeping up with the diet is 2269 calories.
Add a large, 500 ml Coke and that's another 210 calories.
There goes the entire week of dieting, with 659 calories to spare.
That's a pound of fat gained every 5 weeks, while on a diet.
Cause people are not robots. Heck, forget the pizza.
Friends and family will make one eat that AND MORE - out of politeness.
Now, try that same regimen - but with half an hour to an hour of cardio+strength 3 times a week, knocking down about 100 calories and increasing one's activity factor to 1.375.
That's a change of 3*100 calories on exercise, plus an additional 291 daily calorie difference.
Now add that to those 1820 calories from diet alone.
260*7 + 100*3 + 291*7 = 4157 calories reduced, per week. Instead of 1820.
Now you can have that pizza and coke AND lose a pound every two weeks AND gain muscle.
Or just drop that diet and keep it at 2000 calories.
Now... Which one is easier to keep up with?
Making sure one's calorie intake matches one's calorie expenditure 7 days a week - OR making sure that one's BMR is kept a LITTLE higher only 3 times a week?
One is very hard to measure and takes a lot of will power.
The other is relatively easy to measure with a pedometer, a clock, a scale and the ability to count to 10. And it takes a lot less will power.