Hi there! My husband and I are planning our very first trip to Japan for next spring. I have been doing quite a bit of research, but have found no clear answer to one particular question...I am a bariatric surgery patient and eat very, very little. 5-6 bites of any particular food is generally about as far as I can go. I know the portions are smaller there, but are they THAT small? I read several places that it isn't considered offensive in most restaurants to leave food on the plate, but I would literally be leaving almost the entire dish because I eat so little; however, I read that it isn't commonly accepted for people to share a dish (which is what my husband and I usually do), each person is expected to buy at least one thing for themselves. I also don't drink with my meals and am hoping that isn't an issue...I'm just trying to figure out what the best course of action would be for me...I really do not want to be rude or offensive to anyone, it's important to me to respect the customs of the Japanese people while we are there. Does anyone have any insight on this issue? Thank you so much!!

I don't know where you got the idea that Japanese people don't share a meal. That is exactly what izakaya (pub) eating is. Many small plates are ordered and passed around the table.
If you go to a yakitori/robabta yaki/ kushi katsu restaurant you order by the skewer.

If you eat at casual restaurants you shouldn't have any problems with ordering and eating a small amount of food. And if you have some left and your husband eats it that is now perfectly acceptable table manners. Japanese now even do doggie bags.

Japanese easily and freely forgive the etiquette transgressions of barbarians (of which you are one, as am I). They'd be far more horrified if you blew your nose in public or spit in the street.

Westerners get special treatment in Japan--the Japanese are more interested in pleasing you than assessing your manners. My only faux pas was accidentally walking with shoes in a tatami restaurant. That being said, here are my suggestions:

No one will care how much or little you order. When sharing, you could possibly say, "I had a big lunch, so we would like to share one dish."

Stay in hotels that offer a buffet breakfast--the rate is typically only a few dollars more than a basic room rate. I like the Dormy Inns for wonderful breakfast buffets. That way, you can have a few bites, then sip on some tea while hubby eats.

Grocery stores or basements of departments stores, depending on the city, have elaborate take out food sections. You can get a little of this, and a little of that, then you can either eat it at the tables there, or take it back to your room. I do this all the time in Japan, since I am tiny and eat only a little bit at a time.

Remember to take nuts or protein bars, or whatever snacks you like.

You don't need to bring your own snacks on the trip. Japanese snacks are delicious, much better than American ones. Rice crackers, senbei, come in a variety of flavors. You can also get sushi by the piece or in different sizes epacks in grocery stores for a reasonable price.

I always carry my own snacks, even in Japan. There is always a time when the stores are closed, or I am not near one. I especially recommended it for the OP's medical situation, since she can only eat a little bit at a time, and may get hungry when no store is nearby.

I never eat refined carbohydrate snacks. Only proteins or vegetables.

For drinks, you are certainly not obliged or expected to have drinks. On our first trip, the £GBP was weak and drinks seemed disproportionately expensive (whereas we found food the opposite, much less expensive than we'd expected). We sometimes preferred to grab drinks from vending machines or konbini (convenience stores) and have minimal during meals -- in some places cold water or iced tea were provided free of charge. Sometimes my husband would have a beer but I'd be happy with water.

Don't eat/drink while walking down the street.
Don't rest your chopsticks by sticking them into a rice bowl.
Don't blow your nose at the table.
Slurping noodles is good, but no worries if you can't slurp.

If you were satisfied with your meal, then be prepared and say the following to your server at the end of your meal:
oishii katta desu!
long o and e, silent u, sounds like:
o-e-shee kah-tah dess

Meaning: It was delicious!

Oishii!= Delicious!
Oishii desu. It is delicious.

>>long o and e

I mean the i sounds like a long e, like in maxi. The e in desu is short, like in dress.