Well, I think it is possible to gain weight after a hysterectomy, just as it is possible to gain weight without having a hysterectomy... if you know what I mean. I do believe a lot of women use that as an excuse when they start eating too much, but I also believe that taking estrogen can cause some women to retain more weight, plus the fact that it usually gets harder for everyone as they get older to stay slim. A lot depends on your heredity also. My mom was a lot heavier than I am, and she did not have a hyst. I had a TAH eight years ago, at the age of 44, and I weighed about 147. Now I weigh about 160. But I eat the wrong things too much, and don't get enough exercise. So, I can't entirely blame the hyst. Lots of older women like to scare the younger ones too, or make them feel bad, by saying how terrible it is to have a hysterectomy. But, if you need it for medical reasons, then you just have to deal with it. By the way, when did you have yours? What age are you, if you don't mind me asking?
My daughter, who is 29, just had a TAH this last February, and she is taking estrogen. She had several women, one in particular, that told her that she would be sorry for having a hysterectomy at such a young age. Brother! It is hard enough to have to face having a hyst., especially at such a young age, but it is really crummy to try to scare others about it!
Take care, and try not to worry about the weight issue. I don't think it is an old wives' tale (just some of the older women who like to make you feel bad, or hope you will be in the same boat they are). It is really just a matter of how each woman's body adjusts to her own eating patterns, heredity, and exercising habits.
My cousin had a tvh, and kept her ovaries, and she is skinny as a rail, and she is my age now. I have met a lot of older women who are thin, and have had hysterectomies.