I'm 5'0"; my husband is 6'4". I'm female; he's male. We both currently weight 145 pounds.
(Errr... when I started writing this post I was 145. As of the beginning of October I'm now 144. But, that one pound difference isn't enough to negate the overall message of the post I was working on.)
Clearly, that same weight has very difficult implications for each of us!
For me, I'm clearly overweight. Even though I think I have at least slightly more than average muscle mass, I have no doubt that this weight also reflects a percentage of body fat that is too high (never had an opportunity to test it, though I think that would be a useful piece of info to have). I want to blame part of this on my body and poorly functioning systems (hypothyroidism, PCOS, etc.), but it's also the result of many bad habits and a strong sweet tooth, verging on binging disordered eating.
Abe, on the other hand, is underweight. Not only a low absolute number (compared to his height), but he also has a fair amount of muscle mass, so his body fat percentage is ridiculously low. Some of this is just his body type (not only metabolism, but also a narrow frame), but it is also due to an extremely healthy diet, full of vegetables that are nutritionally dense but low in calories. I wouldn't go so far as to say he has disordered/orthorexic eating habits, but he definitely has some tendencies to overvalue micronutrients at the expense of the overall health picture of a meal or day of eating. He's not going to turn down a burger if that's the most available option, but given the choice he'd much rather eat a salad full of greens.
I know I need to lose weight. He knows he needs to gain weight. We're both trying to support each other, but these opposite needs make for an odd dynamic. I know I don't want him sticking his nose too far into my food choices, but I also want to be encouraging to him and make suggestions to help him with his goals (you need to gain weight? oh, I know how to gain weight). It's an extremely fine balancing act. I've heard of spouses or friends supporting each other in losing weight together, but in that case they're reinforcing the same habits for each other. In this case, I've joked that we ought to just each plate up food for ourselves, and then trade.
But, though my situation may be more typical in today's society, both of us reflect a not-quite-right relationship with food. He's all about optimizing nutrients, I'm all about maximizing enjoyment. Neither one of us is balanced, and that's reflected in our bodies. Our bodies should be able to find an ideal equilibrium, not too much or too little fat, if we found an equilibrium with our habits. In that sense, we both have the same goal, we're both trying to find that middle ground, even though we're coming towards it from different directions.
How would you recommend supporting a loved one when you have opposite approaches, but are both trying to be healthy?