When you placed your scrawny hand on my arm and expressed concern over my weight, it hit me harder than you will ever know.

Where to begin? Perhaps the first point is the fact that I am well aware that I am fat. The painful rash due to my thighs rubbing together under my summer skirt drives that home perfectly well, thank you. So why do you feel it's OK to point it out to me? Our relationship isn't the place for a hideous American "intervention" – as if I am out of control and need reining in by someone else.

I thought you were my friend. I can shield myself from the ugly insults of the general public, tell myself they don't matter and that fat is a feminist issue, but with you I imagined I was safe to let my guard down, to relax without being judged. I thought friends didn't criticise each other. It wasn't just touching a nerve, it was like 10,000 volts rattling my whole body.

It has made me wonder whether my size embarrasses you? Is that really why you brought it up, under the guise of concern over my health? It's true I feel ashamed when we're out together and I catch sight of us in the mirror. "Willowy lovely plus hefty sidekick" is my imagined caption. But I had hoped that you weren't bothered, and liked me for me, rather than for my appearance.

It has made me cringe for every cake I have baked for you, every meal we've shared. Were you totting up the calories with my every mouthful? I used to enjoy our conversations over lunch. I never realised there was an elephant in the room – and that it was me.

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