It will be hard to pick apart why. Muscles increase metabolism plus I suspect after a workout you feel like protein not carbs/sugar. You eat that and feel full. Then there is plain old confounding of people who have a good diet and people who exercise.

I think weight loss is more than just calories in/out. Maybe our body reacts to adapt to situations and tried to change the body shape to make it easier for itself. So I think healthy habits are more important and can depend on genetic history too.

I think emotions are a huge part of weight gain and loss and yet most Western medicine seems to almost completely ignore the impact of emotions on the body. Try eating a lot of food when sad—it's hard to take even a bite. Yet it's hard to even realize just how much one is eating when anxious.

I also imagine the emotions impact digestion and storage of fats and a lot more, basically adapting our bodies to our perceived environments, so it kinda baffles me that we don't study the emotional impact more.

Yes, I agree. I feel we are definitely missing out.

A clear example is something like cortisol. It damages your body to give you a short term advantage to survive a situation.

Being under stress might make you burn lots of calories, but stress ends up being weight gain in the long term because the body tells you to save up more energy for next time.

I am fairly certain I know the answer to this. They normally do these kind of studies on untrained humans, because the point is to prescribe (or not) exercise to people who need to lose weight, which are typically not athletes. The anecdotal success comes from people who play sports (tautologically). The problem is you cannot compare across these two groups because the metabolism and sheer volume of exercise is not comparable. Even a semi serious athlete will put in 5-6 hours of intense training a week. And their bodies are much more efficient, so they can burn way more calories in the same time. This is NOT the same as “Brisk walk and lift some weights 3-4 times a week” they prescribe the study group in a study of untrained athletes. Not even close.

I mean the typical advice I get is 1 hour of running burns as much calories as one large slice of pepperoni pizza (~700 cal). Trained or untrained, this seems off by a lot.

Why does it seem off? It's hard to measure calories when running, but with cycling we have power meters which are incredibly precise, and you will burn around 700 calories an hour (as a beginner). Trained athletes can burn maybe double of that.

Because it burns off about a whole large pizza's worth, rather than one slice, and I'm not trained.

Folks who can be bothered to put in the effort to commit to regular exercise are more likely to be able to be disciplined about what they eat. Levels of exercise are probably pretty well correlated with folks who are serious about their weight.

What do you think about sports (say badminton) compared to treadmill or cross-trainer for cardio?

If I end up burning the same amount calories? Because I find it much easier to burn calories playing badminton compared to treadmill..