People know when they are gaining weight. It is not some mysterious affliction that you need to bring to their attention. They don’t need tips and tricks. They don’t need lectures on exercise. This is knowledge we all possess. You need to realize that sometimes the solution to an individual’s health puzzle is more complicated than diet tips and exercise. There could be a lot going on that you don’t know. Trying to solve someone else’s health puzzle without their consent and without the whole picture can be intrusive and upsetting.
If it is a health concern, that is something the person will address with their doctor. You can be big and healthy. You can be skinny and unhealthy. It is not your place to make assumptions about one’s health. But if you make them feel ashamed of themselves, you could contribute to making their health worse.
The answer is quite simple, really.
Treat them with respect and support them if they ask.
Wise advice :).