Shinamae Whenever you want to lose weight, and do it successfully, there will always be the Job's Comforters that tell you that isn't worth it and you will only put the weight back on again.
Yes, many people do put weight back on after a diet, but that is because they see a diet as a 'quickfix' and then go back to the eating pattern they had before, which put the weight on in the first place. And to be fair, many of the people who go on Slimfast and other special food/drink/powders to lose weight quickly are doing it just as a quickfix. and then return to their old eating pattern.
But, providing once you have lost the weight, you adjust your continuing eating pattern to keep it off, you should be fine.
I lost 2 stone 9 years ago, using the original 5:2 diet and have not put it back one, so Good Luck, I hope you lose the weight.