I offended my body conscious boyfriend. What do I do?

I offended by body conscious boyfriend by mistake, and he said it was something that would stick with him for a long time. Long story short, he is huge on building muscles, and has been 'bulking up' in order to do so. THis has led to fat gain as well, which he is aware of, and often jokes about developing a double chin and a new roll on his stomach. I made an offhand comment in the same context, and he said it really hurt him, and how badly he wants to take steroids to get the perfect body. What can I do?
I offended my body conscious boyfriend. What do I do?
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