Some people are really lacking in empathy, sheesh.
I consider myself an empathetic person, but, it's true, there have been some things I don't fully understand unless I or someone close to me experienced them. Some examples are: before I had children, and when I saw a parent really struggling to try and manage a difficult child, I would wonder why the heck couldn't they control their child! Now that I am a mother, let's just say, man, I really know what that's like... now, I'm like, how can I help! Another example is sympathy for chronic pain sufferers, and everything that goes with that - I watched my sister deal with 10 years of intractable pain and multiple back surgeries. I also have a lot of sympathy for smokers trying to quit, having watched both my parents smoke for decades, then try to quit, and then finally successfully quit.
And then, obviously, I straight up know what it's like to be obese

The complexities of one's relationship with food in this and instances of eating disorders are vast. I think your friend said outloud what a lot of people actually think. It REALLY pains me to know that obese people are thought of as gluttonous lumps : / I have read a few studies on prejudices toward obese persons and, frankly, it's beyond upsetting. The worst for me was reading what nurses and also teachers thought of the obese. I found it demoralizing to read. These opinions are pervasive, and I wouldn't waste time or energy on the disturbing comments your friend made.