sometimes we don't actually give the pigs diabetes to study it- for example I just met two pigs the other day who had surgery on their aortic valves to increase their blood pressures so they'll resemble that of an obese person's.  In theory, diabetes is reversible if you lose weight, but so few obese people are capable of it. Fewer than 1% I have heard, which is bizarre.  Also in theory if you starve a creature it will eventually no longer be obese, though some tumblr posts would lead you to believe otherwise. :)