Make the choice not to body shame or diet shame.
Make the choice to recognize that different people have different metabolisms, meaning that they can be obese while still maintaining a “healthy” diet or they can be thin while still maintaining an “unhealthy” diet.
Make the choice not to judge people based on purely shallow aesthetic standards.
Make the choice to see that one single meal is not an indication of a person’s overall health, nor waist size as legitimate evidence of anyone’s medical wellbeing. Unless you are intimately aware of a person’s medical history, and unless they have specifcally asked for your opinion, then do not comment on their bodies or express your thoughts regarding their health.
And most importantly: Make the choice to admit that the “right” choice is going to be different for everyone. Learn to respect that.