Hi RS

My Alex would tell you the don'ts first
Don't fuss, don't work your way down a mental list of possible food options making suggestions - ask him what he wants and if he doesn't want anything, shut up and move to the next topic. Don't fuss. Don't watch him when he eats or drinks. Don't fuss. Don't tell him how he must be feeling, and don't fuss.

From me, maybe getting your brother to tell you how you can help him before the situation arises would make things easier. For example, you might ask him what he eats (if anything) whilst you are sitting watching TV and a food advert comes up. Don't wait until you are about to sit down at the dinner table. Does he have a favourite drink, can he explain what the issues are with eating/feeding so you can understand and does he have any tips for helping him. My Alex prefers slightly fizzy water over still, hates when I ask him what flavour yoghurt he wants because he can't taste the difference, can't bear me eating eggs because he can't handle the smell (this week anyway). Your brothers preferences will be individual and you will only know if you ask.

Lastly, treat him like your brother not a sick person and ask him about his needs, energy levels, expectations etc, before you inadvertantly put him in situations that are uncomfortable for you both.

And of course, listen to him and encourage him to talk about his experiences and feelings (if he is that sort of man)