1. "You've put on weight."--Even if it doesn't seem like it, your partner is aware that they've gained weight. Also, the weight gain may not really be about food. An increase in size is often a side effect of emotional eating. So if your partner has put on weight, they may be turning to food to cope with something else that's going on. Communicate openly with your partner and get them the emotional support they need.
2. "You shouldn't be eating that."--The best way to help is not to point out what your partner is doing wrong, but instead consistently and casually offer healthy options in a non-judgmental fashion. Even just making healthy foods accessible can help a lot, like putting a fruit bowl on the counter top, or putting ready-to-eat fruits and veggies in clear containers on the top shelf of the fridge.
3. "Haven't you had enough?"--Monitoring portions tends to lead to the same anger tied to policing "bad" foods, and can lead to secret binges or overeating when the partner isn't around. So even if your partner asks, don't agree to take on this role. Instead, try practical ways to curb portions, like using smaller plates, breaking up leftovers into single, smaller servings, and reducing portions of starchy foods like pasta and rice.
4. "It's easy, all you have to do is…"--While some people can manage their weight pretty effortlessly, it's a real struggle for others. The truth is, weight control is a lot more complicated than calories in, calories out, or eat less, move more. Plus, what works for one person may not work for another. Instead of trying to school your partner in what works for you, try to examine what works for them.