The only way to lose weight in a healthy and sustainable way is by eating less calories.
DO NOT drop calories by a crazy amount but maybe by a couple hundred a day. For example if you are someone who can maintain your weight at 2000 calories a day, you can diet on 1800 calories instead.
My wife is on a routine like this.
The problem with starving yourself say on 1400 calories a day is your body gets used to receiving such low calories and when you end your diet and start eating more you gain a bunch more weight.
I know very little about this but a good, knowledgeable nutritionist can put you on a deficit/diet and reverse diet plan.
Also note: it’s ALL about calories. If you got the proper protein and fat you need, the rest of your diet could be sugar and if you were in a proper calorie deficit you would still lose weight.
Also see: Cocaine use