Why is it often that people get a metabolic chronic problem after they diet?

What do you mean by a “metabolic chronic problem”?

Also, what evidence do you have that this happens?

I know of at least three people who had problems with different glands such as the thyroid gland a short time after they lost a lot of weight. Definitely, I don´t have evidence and that´s why I posted the question. Sorry for not being very precise, as it´s only a vague idea. I´m asking it because I am concerned to see those things happen to people. I would also obviously like to avoid it happening to myself anytime in the future.

Do these people go on extreme diets?
Did the diets cause the issues, or were the just issues diagnosed after dieting?

These people followed a diet their nutritionist gave them.
There is no explanation as to whether the diets caused the issues.

Weight loss is implicated in some conditions- for example, I’ve lost a lot of weight in the past year and a half and began having gallbladder issues, and there is medical evidence to support a link between weight loss and gallstone formation. But without a lot more specifics on exactly what happened, it’s impossible to give you much evidence.

I have heard that people can develop thyroid trouble after extreme dieting. Pretty sure Elisabeth Hassleback claims that happened to her after being on Survivor. But, possibly they found the problem when she was dieting, and it did not cause it. I would say never do anything very extreme because it is a burden to the body. When people lose weight the body has to adjust to the changes. It is balancing electrolytes, which is part of the reason people lose a lot of water weight at first, hormones change, because some hormones are stored in fat, and metobolism might slow due to less food intake, and nutrition might suffer on a very low calorie diet, and some nutrients have a causal affect with hormomes. Vitamin D affects the parathyroid function for instance. Sometimes when you challenge the body too much, I guess there is a possibility it might cause permanent damage. But, I believe in the bodies ability to heal, I think most of the time when we start doing the right things again, our bodies can go back to normal.