HIIT and weight loss?

HIIT is good because 6 intervals which take about 20 minutes can burn as many calories as walking for an hour. The other advantage of HIIT is that it is resistant to Adaptive Thermogenesis, meaning that your metabolism cannot adapt to the increased calorie burn from HIIT. Steady state cardio is different because your body can adapt to it. For example. If you burn 300 calories every single day by running at a steady pace for half an hour, over the course of months your body will end up burning 300 less calories a day to account for that cardio that you do every day. If this weren't the case, then there should be absolutely no way a marathon athlete should be able to eat enough to maintain his/her body weight, but they can because their metabolism has adapted to their cardio level. HIIT on the other hand is resistant to this. As for the "afterburner effect" from HIIT, it is way overblown. Yes your metabolism is increased for a period of time after doing HIIT, but it is usually around 10% of the calories burned from the HIIT session. If you burn 400 calories doing HIIT, over the next 24 hours or so your metabolism will burn an additional 40 calories, which is pretty negligible in my opinion.

My HRM is not telling me I am burning a huge amount of calories when doing HIT, but I hear it is good for fat burn and revving the metabolism. How can this be when I am not burning nearly as many calories as I would when doing 60 minutes on the elliptical? I am generally burning half or less. I thought weight loss was calories in versus out? Help!

Weight loss is about a calorie deficit, and to be honest as a high intensity intervals workout is quite short you're probably burning about the same in 20 minutes as you do in 25-30 minutes of moderate intensity steady state.

The benefit of high intensity intervals is the effect on your VO2 max if you train to a HIIT plan over a course of 12-16 weeks.

The evidence around EPOC is divided, but the majority suggests a negligible impact.

fwiw the idea that your body adapts to steady state is inaccurate as well. Your body doesn't magically start saving calories elsewhere.

HIIT is useful, but it's not magic.

HIIT is all about intensity. You are alternating 100% effort for a period of time with rest for a period. And 100% percent means 100% in that it's everything you have; so much work that you can't even speak.

A typical HIIT workout is something like a 5 minutes warm up, 30 seconds full intensity and 1 minute rest (for 10 minutes), and a 5 minute cool down.

Just to echo what MeanderingMam wrote, HIIT or any exercise is more about about fitness than wieghtloss. Diet is 90% of weightloss and can be achieved with zero exercise.

This^^

When I do HIIT on treadmill, I usually alternate between 1 min of 4 mph and 1 min of 9.5mph(like 6:15 per mile pace). I am usually out of breath during the high minute. At first 1 minute of rest didn't seem enough to get my heart rate down but a month later it was enough my heart rate could be change from 180 to 120 within seconds...