DP and I were talking about what the problem with MiL is and DP I think has it nailed. This next bit is going to sound really big headed but it's the only way i can explain what he thinks is going on 
MiL is the odd one out in her family. SHe's one of 4 and her brothers and sisters are all working class, very proud of that but they all come from nothing and have very little.
MiL worked her way up through the NHS and takes great great pride in being "the clever one" who got off the housing estate they all live on if that makes sense. She has always been revered by everyone she socialises with as "above" them in some way and she takes great lengths to maintain her reputation as an authority on most if not all things. DP was the first person ever in their family to go to University and is the only one of his generation to have done so.
I, on the other hand come from a family where both my parents went to Uni, my Mum has 3 degrees, 2 masters degrees and a PhD in biochemistry and my Dad was a university lecturer for the bulk of his career. Both are from working class roots but couldnt be described that way now and I was certainly brought up in a firmly middle class household.
I have my mums brain in my head so I love science, numbers, data and facts and when I was 17 (when i met DP!) until I was about 21, I didnt understand that challenging MiL when she stated utter shite as fact wasn't the best idea. So our early relationship was rough. When she was wrong I'd tell her she's wrong and did that a few times during family games of trivial pursuit etc. As a result, I'm now known as the clever one to DP's family and MiL isn't asked for information anymore, I am. 
.. recently one of DP's cousins needed help on her uni course and she rang me, not MiL. According to FiL, MiL was upset about that.
Now I'm a lot more placid than i was back then and I can keep my mouth shut, but I think MiL does still feel threatened at times. The daft thing is, we're really really similar in personality and I really look up to her strength and determination, she's a force to be reckoned with.
I reckon her issue with the food thing is that this is just something else I'm doing well that she struggles with. It's another thing I disagree with her on and she's choosing to view it as "jim thinks she's always right".. and my results are showing now so it kinda proves that in this case, I AM right.
I think she therefore sees my success at the moment as a reflection of her failure to lose weight, so the "everyone noticed" comment was probably more aimed at herself and her own insecurities.
I'm not really sure how to fix it. DP says it's not my fault, I'm doing nothing wrong and I just need to leave it and let her get over it in time. I hope she does because I genuinely love her to bits!
Argh. Bloody nightmare!