“recommended going no more than 500 calories off the weight maintaining level of calorie intake for dietary purposes”
This doesn’t make any sense, from the standpoint that fasting is a perfectly healthy and acceptable method of burning fat, and has other health benefits as well.
As a practical matter, the number of calories needed to simply maintain a given weight is (for most people) surprisingly low, and the subtraction of 500 calories from that figure would still put it in line with weight loss calorie recommendations going back almost a century.
600-800 calories for rapid weight loss, maybe 900-1100 for moderate rate weight loss.
BMR stands for basal metabolic rate. It is the minimum number of calories that your body needs for basal functions like breathing, digesting, and keeping the body temperature steady over a day.
Counting your BMR can be a good starting point if you want to lose weight. First, it tells you how many calories your body needs to function properly, so you never want to eat less than that. Then, if you multiply it by your physical activity level (PAL), you know how many calories you actually burn each day. Subtracting a reasonable number of calories (e.g., 500 kcal/day) will let you lose weight gradually and steadily.
One of the advantages of the Harris Benedict Formula is that it gives you an estimated amount of calorie intake based upon your activity level to maintain weight.
https://www.omnicalculator.com/health/bmr-harris-benedict-equation
In general, if you cut about 500 calories a day from your usual diet, you may lose about ½ to 1 pound a week. But this can vary depending on your body, how much weight you want to lose, your gender and activity level.
It sounds simple. But it’s more difficult because when you lose weight, you usually lose a mix of fat, lean tissue and water. Also, because of changes that occur in the body as a cause of weight loss, you may need to decrease calories more to keep losing weight.
The body will protect itself even from dietary changes. A person generally wishes to lose weight because they, or someone else, noticed they have gained too much. This can include anything from appearance to physical needs. But when the body realizes it is being underfed from the norm, it will in time start to horde calories making harder to maintain a steady weight loss. This will cause a greater amount of calorie cut to continue the consistent reduction in weight. And the more calories that are removed from the diet, it will cut that safe and consistent loss. Remember my doctor friend? He found out the hard way on extreme calorie cut diets that his energy and strength level dissipated to the point of muscle failure because his expectation of loss were to great and too quick.
Excess weight, whether it exists or not, didn’t get there overnight, it won’t come off overnight either. At least not safely and still maintain a comfortable lifestyle without cravings and setbacks not to mention the violating of your DNA determination of body shape and size.
Severely restricting your calories can decrease your metabolism and cause you to lose muscle mass. This makes it more difficult to maintain your weight loss in the long term.
https://www.healthline.com/nutrition/calorie-restriction-risks#TOC_TITLE_HDR_3
Wy69