Oh that coment must have felt dreadful. Think i'd i've got out and said something along the lines of, "I know you're my mother and i love you dearly, but f off" in a rather hostile tone.
What a horrible thing to do to you! I'm sure that there is something with mothers and weight loss as mine is the same, never got a good word to say and she can be a right nasty b**ch when it comes to my weight, problem is she weighs almost as much as me!.
Keep going with your weight loss you're doing really well, don't let it get you down!