There's nothing awkward about it at all, nobody deserves to be bodyshamed, period. Yes, being overweight is unhealthy. The vast, vast majority of overweight people know this. The only thing you accomplish by expressing your concerns and "acknowledging it's bad" unprompted is making the person feel worse, they're not gonna go "Wow, li10 is concerned about my weight, this was the moment I was waiting for to start being healthier". This isn't a hallmark movie, it rarely works like that.

If an overweight person expresses a desire to lose weight and be healthier, absolutely encourage and support that... but support looks like things like offering to be a gym buddy,sharing healthy recipes, words of encouragement as they progress, maybe even joining them on their diet, etc... and even then only if they've expressed a desire for that support. Telling them unprompted "I'm concerned about your health due to your weight" is NOT support, it's nothing but an empty platitude.