Confusion about training intensity and weight loss

It won't.  They're operating under a common misconception that gets thrown around a lot.  Here's the deal.  As a percentage of total calories burned, more fat is burned at lower intensities than at higher intensities.  As a total, more fat is burned at higher intensities.  I know that's hard to follow for people sometimes, so numbers help.

If you exercise at "low intensity" for an hour and burn 300 calories, 70% of which are from fat (totally made up numbers just used for an example, you'll burn 210 calories from fat.

If you exercise at "high intensity" for an hour and burn 700 calories, 40% of which are from fat, you'll burn 280 calories from fat.

Some will stop at seeing 70% vs. 40% (again, just example numbers) and proclaim lower intensities better for fat loss.  Don't be fooled.

Blood glucose first, then stored glycogen.  Very small amount of protein.  The reality is that you can't really separate out any of it.  It's all occuring at the same time in varying amounts.

Pretty sure the answer to that is, it varies based on your fitness, nutrition, weight, etc.

Warning: unresearched third-party information....

But also consider that higher intensity workouts up your metabolism longer, and generally produce greater muscular increase.  It's not just calories/fat used during the workout that matter.

That said, workouts should strategically involve easy, moderate, and intense effort... too easy too much and you're not getting the most out of them... too intense too much and you'll burn out or get injured.

It differs.  The higher percentage of fat that one uses at a given intensity the better for an endurance athlete as you don't use so much of the limited glycogen stores.  Is that not the purpose of the LSD sessions - to train your body to use a greater percentage of fat as a fuel?

I experience the exact same thing - too much intensity results in near uncontrollable hunger. This is not just a "mental thing" or a willpower issue. What happens at very high intensities is that you burn through a large percentage of your glycogen stores, among other things. Your body wants these stores back, so you get hungry, mostly for carbs and sugary things. At lower intensities, your body will shift to fat burning more quickly, leaving some glycogen available. I've noticed this in my own training - I can eat a relatively low carb diet and still train as long as I keep the intensity in check.

The other thing about high intensity cardio workouts is the burnout. You simply cannot run sprint intervals every day.

As a practical matter, I've found that mixing it up is a good way to go about this. Some days, especially those days when I've eaten more than I should, I may do a high-intensity interval, while other days I slow down and increase the duration.