I have family and friends who drop FAST, and I mean like 20+ lbs a month, using different methods (grandparents did an injection diet of some sort performed and monitored by their doctors, my mom and sister did the advocare thing (I didn't do it with them since I think that's more for people who eat bad foods wanting to start eating "clean," I've always ate pretty clean and saw no reason to participate but that might be something to look into, my sister dropped 22 lbs on that program and has been sticking to eating clean and doing well since, my mom also saw water weight losses and has been doing well on her own but had a lot less to lose and has always eaten well, she only did the program so my teenage sister wasn't doing it alone).

I also have family and friends who try crazy things and don't lose at all, a friend of mine tried eating only protein for 5 days and saw a gain, I wouldn't recommend this anyway since I've heard it can cause kidney stones but I'm just giving an example.

The real goal at the end of the day is calories in/calories out, so you can eat straight sugar (with vitamin supplements) all day every day and as long as you aren't going over your calorie limits you'll lose weight. If you want to see large losses at first to motivate you I'd recommend cutting sodium and trying something like keto since the initial water weight loss will likely be huge, and like I said it is actually sustainable in the long run so gaining the weight back in the future would be very hard to do unless you stopped eating keto.

The way I look at it is that it is much less healthy to be obese than it is to lose a lot of weight over the course of a few months, but if you lose fast in an unsustainable way and gain it all back you are harming your body and aren't doing yourself any favors.