Eating below your BMR is unsustainable. While yes, you will lose weight, in the long run it will hurt you. Studies show that people who go on a too aggressive diet, usually end up gaining the weight back up. Most people will feel lethargic, tired, and constantly hungry, with the body also not having the energy in order to do much in the gym. Hence, most people will just give up and go back to their old habits. Losing weight should be done in a sustainable way.

Why would someone wanting to lose weight need tobeat MIRE calories than their BMR? It does not make sense. Someone wanting to lose weight will lose weight faster the more calories BELOW their BMR they eat. The way it’s presented there would be a range of calories to eat to lose weight when in actuality only one criteria has to be met – eat fewer calories than your maintenance calorie count (and the greater number of calories below the maintenance calorie count one eats, the more weight they will lose).

I am a bit confused with what you mean. Yes, your BMR is what your body burns just doing basic bodily functions like breathing. However, throughout the day, you also do other things than just lie still and breathe. You also walk around or play sports. So your body needs to expend further calories in order to cover those activities as well. Your BMR + the calories your body needs to spend in order to cover the more active activities like walking around = your maintenance calories. Basically, your maintenance calories is the amount of calories that you need in order to maintain your current weight.