look at your double chin
have you gained weight recently?
hey! you're so fat!
you may need to do sth
you may need to lose some weight.
you should / ought to do sth
i think you should /ought to do more exercise.
you'd better (not) do sth
you'd better not drink so much beer.
how about doing sth
how about having more vegetables?
would it be a good idea to do sth
would it be a good idea to go to the gym?
if i were you, i would (not) do sth
if i were you, i wouldn't eat too much.