How's your heart? I hear that rapid weight loss is not good for your cardiovascular system.
No issues from what I can tell, early 20s when I did it a few years ago, wasn't diabetic or had any other health issues at the time other than being a lard ass. I think the concern for that is generally if you're not
that fat because then your body might be more willing to go to muscle for energy over fat if you're closer to the line of being slightly overweight vs absolutely obese, less of a concern if you have plenty to spare. Also it's a concern if you're not getting enough protein, which if you're not eating right, could absolutely happen on 500 cals a day.
500 kcal in chicken is about 200g of chicken, you really need to be a desperate fat fuck with a lot of willpower to pull it off because 500 calories a day is very little food. 1200 ~ 1500 calories is still the sweet spot imo. You will lose weight, it's more manageable and you'll learn how to eat like a human being again. I've tried one of these crash diets before, gained all the weight back.
Ideally people should just find a diet they will be able to sustain for months and stick to it, the only people who go from one diet plan to another are fat people who never lose the weight.
Yeah, I don't know if I'd recommend it, but it is doable. Much like people fasting, after I got going on the diet for a few days I felt great, had pretty much zero change in energy and didn't feel hungry except for the two times a day when I would eat. (100+g of lean meat with vegetables for lunch, 100g+ of lean meat with vegetables for dinner, sometimes a apple or something for breakfast if I felt like it)
And yeah that's fair about gaining it back, I got sloppy and gained a bit back, but I hate when you read about doing a VLCD and almost instantly you have redditors screaming from all corners of the internet about how "YOU'LL GAIN IT ALL BACK!!!" Like your body is magical and it gets mad at you and instantly atomizes fat back onto your ribs for "starving" it. If you go back to eating like shit, yeah, you'll gain it back, calories in, calories out, simple.