Is it OK to tell your friend or a family member to lose weight?

The other day I suddenly noticed that my friend has gained a quite a bit of a weight. Needless to say that her food habits are way out of control and there is no exercise plan in her daily life. I was concerned about her health. She has not yet it 30 and so much of belly fat can only be harmful. A part of me said to tell her and a part of me thought if she is happy with it why should I bother.
So what do you think? What would you do?
Is it OK to tell your friend or a family member to lose weight?
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