Why is hitting macros good, and fasting is good, but eating like 500 calories a day is generally frowned upon?

Ugh, so much to unpack here.

Calories have nothing to do with ketosis. Carbs do. That's why the ketogenic diet works. It's called nutritional ketosis.

If a person is eating less than 20g of carbs per day, they will be in ketosis. So they can eat 500 calories, and their body will make up the deficit from fat reserves. They are not starving and their body will not go into starvation mode because it is getting all the energy it needs from stored fat. This is why the ketogenic diet is so effective. You don't feel hungry when you eat less because your body is still getting what it needs/

Eating only 500 calories a day is bad if you're eating the Standard American Diet. If you're eating keto, and you have enough body fat to sustain your energy requirements, it's perfectly fine.

/r/fasting Thread Parent