I couldn’t tell from the article how 3, 4 and 5 are different other than by degree. 1, 2 and the final 3 all have different mechanisms so I could see three types, but not 5 types.
The degree of body metabolism. Group 3 has more severe metabolism problems therefore “diet and exercise” doesn’t work and neither does medicines. Moderate exercise has no effect on weight loss either. So it is the severity and group 5 tends to be later in life.