The question: What is the best time of day to exercise, if my goal is weight loss?
The answer: Before breakfast.
The evidence: a study of overfed Belgian men in 2010.
"researchers in Belgium persuaded young, healthy men to stuff themselves for six weeks with a diet consisting of 30 percent more calories and 50 percent more fat than the men had been eating."
Was not kidding about the overfed. Meant that literally.
So obvs, a bunch of these guys gained weight.
"But the men who had exercised first thing in the morning, before eating anything, had gained almost no weight and retained healthy insulin levels. Their bodies were also burning more fat throughout the day than were the other men."
What was going on here? Okay, well, if you overeat by that much, YOU DO NOT WAKE UP HUNGRY. You may well wake up kind of uncomfortable. You can blow through this, eat, carry on about your day, etc., but you don't wake up hungry. (If you never wake up hungry, you might seriously think about WHY you never wake up hungry. And whether you, like these young Belgians, might be eating a bit more than you should.) I can readily imagine that blowing through that residual blood sugar would really help with a lot of things.
But suggesting this as a tactic for someone who is weight stable (and thus _not_ overeating for their size/shape/activity level) isn't necessarily going to work the same way. You take a hungry person who just woke up and send them out to exercise vigorously, and you should probably expect a higher rate of injuries and accidents.