I feel like this is a topic that needs to be addressed. I know that it can often be a difficult conversation to have with someone in your life who is not the ideal or optimal weight or body type—whether it be in your opinion, the view of society or otherwise. Here I have created a short, easy to follow, 3 step list that guides you through the correct route to take in order to talk to someone about their body and weight.
First, compliment them on something that is not physical. This is not a sometimes implemented, optional step. This is a full time, necessary step. Just recognize what an honorable person they are, through and through. Tell them how proud of them you are because they are always so kind to others, never leaving anyone out. Tell them that you appreciate how much they console you when you're sad and make you laugh until your stomach aches every time you get to go out on the weekends. Let them know that when they talk about their new research project, career path, or travel opportunity that their eyes light up so bright that it makes you just as excited too. Tell them how much you admire their intelligence, diligence and passion on these things that they care so much about.
Second, ask about their feelings. Not necessarily about their physique. Just in general. Check up on them often. Show them your companionship and commitment to the relationship that you hold with this person. See them as their own person and appreciate them for this without juxtaposition. Realize that they are entirely made up of their own components: biologically, mentally, emotionally, environmentally, situationally, and otherwise. Learn to not base this person off of yourself or anyone else — simply because it will be flawed and skewed in comparison, 100% of the time. Accept this and carry on with the wonderfully individual and one of a kind relationship that the two of you hold. Humans aren't synecdoches. Quit obsessing with the parts and appreciate them as a whole.
Third, some internal assessment. Consider the following:
"Is this any of my business?"
"Does this person's body affect me?"
"Did this person ask for my advice/opinion on their body/weight?"
"Does this person's body type affect who they are as a person or how they treat me?"
If you answered no to these questions, which you most certainly will, the last portion of this application is absolutely crucial.
In summary—if you aren't understanding by now—the best, easiest and most effective way to talk to someone about their body and weight is simple: DON'T.
Neither weight nor body type dictate the value of a person. Your looks do nothing when your character and soul is what truly defines you. Comparison is the root of self-loathing. Most importantly, there are much more important things to be in this life than "skinny," or "curvy," or "muscular," or "handsome," or "pretty." Love the people that you love simply for who they are, beneath the superficial layers — and never let them forget it. It absolutely hurts, all the time, to be called out or put down by someone who is supposedly in your life for enhancement, happiness, support and love — whether that is your intention or not.
Society fucking sucks as it is. We don't need any more scrutiny than we are already subjected to. Be gentle with one another. Let's change our minds, change our tactics, so we can change the world.