An hour exercising is an hour you can't eat in addition to likely sleeping better and longer. You can see this people who hike the Appalachian Trail as well as athletes who train at least 4 hours a day.

I have been experimenting with walking 10+ miles a day (at least 3 hours) and seem to lose weight no matter how hungry I get.

Sleeping can assist with general decision making, and yes removing yourself from food options will obviously help you with a calorie deficit.

However neither of these show the GPs point of "exercise is one way to lose weight".

> You cannot entirely ignore diet and still lose weight, even with hours of exercise. Two American donuts are 700kCal.

100% correct, the only time I've out exercised a bad diet was when I was I was bicycle touring and doing 6+ hour rides each day.