The very low calorie liquid diets
I won't name them but there are several out there. You buy nutritionally-complete shakes/soups/drinks and use them in place of some of or all of your meals.
You lose weight very rapidly. But here's the catch. You can't eat like that forever, and at some point you will go back to normal eating.
By then your body is in starvation mode, so it will grab on to all the extra calories coming its way and when you put your weight back on, you'll end up heavier than you started.
So here's the disclaimer; that's my personal opinion, based on personal and professional experience. You will undoubtedly lose weight and you'll laugh at me, but a year down the line you will see where I'm coming from.
So in a few situations this will work well for you. If you are desperate to get into a size 8 wedding dress and you don't mind putting the weight back on once you are cosily embedded in matrimony.
Or if for a couple of weeks you want to get into a bikini for a special holiday. Or when you're advised to do so by specialists, before you have gastric weight loss surgery.
But generally, for most of us wanting to lose weight and keep it off in the long term, it's unlikely to be the right diet.
So go forth and diet! Aim for a slow steady weight loss that you will be able to keep off - one to two pounds per week. Make the changes that you can stick with. Be sensible and safe. Good luck!
And if you hear of an effective diet that lets you have unlimited chocolate, pizza and wine, please give me a call.