Not quite sure what you mean by "permanent metabolic damage" from weight loss. Such an effect does not exist to my knowledge. If one simply doesn't eat enough to get necessary nutrients to survive, that is obviously not a good idea, but overweight people who lose weight safely almost always benefit. Exercise, eating healthy foods, and reducing one's calories are all important. There is plenty of information from weight loss groups, health authorities, and so forth, as well. Obviously, you do need to be sensible when losing weight, but I wouldn't let fears of "metabolic damage" stop weight loss.

Most metabolic diseases are more likely at higher weights, not lower ones.