A few comments saying 'fat people know they're fat, they don't need to be told'.
Some do, but plenty don't. I remember reading some research not too long ago (can't seem to find it now) that examined the opinions of women of various BMI scores on their own weight and the categories of underweight, healthy, overweight, obese and morbidly obese. Loads and loads of women who were obese thought they were merely somewhat overweight, loads of women who saw images of someone who was overweight thought they were normal weight. Very few people were actually self aware enough to be able to say yep, I'm obese, or I'm overweight, instead often blaming the tool and saying it was too strict or unfeasible to be a healthy weight.
Research studies have indicated that someone who is aware that they're overweight or obese is more likely to lose weight, someone who is overweight/obese and perceives their weight to be 'normal' or healthy is more likely to gain weight. Hence why doctors assess for a patient's awareness of their size by asking 'how do you feel about your weight?' because people who are in denial or unable to recognise that they are overweight/obese need more focused attention to help them recognise and come to terms with the reality.
I'd never advocate for someone walking up to a stranger and calling them fat, that's horrible and I know it happens. But we do need to be able to listen to actual doctors when they try initiate a discussion around weight instead of crying 'fatphobia', we do need to empower people to have gentle and respectful conversations with loved ones who are ballooning to see what else might be going on and whether they need any assistance or support. It shouldn't be a taboo topic, especially when it's the majority of the population that are overweight or obese.