Of course you have transparent food
Your question is “what transparent food can transparent humans consume”. The answer is “whatever food you want”. It’s your world. You decided there would be transparent humans. If you want to decide there is transparent food, I don’t see how that would be a problem to anyone. The hard leap of faith is to believe in a fully transparent body (complete with transparent bones, transparent blood, etc, etc). If you’re comfortable making your reader accept that, there’s really no problem in telling him that some pigs are transparent too.
If you feel the need to “justify” the existence of transparent food
Again, you don’t need to. You can just say it exists. But if you think it needs to be justified, nothing more straightforward, since you already consider having transparent humans. If we assume your humans have naturally evolved to be transparent, then there is a whole evolutionary branch of mammals that is gradually more and more transparent, all the way up to transparent humans. 759
You have plenty of transparent cattle, because somehow developing a fully transparent body is a huge evolutionary leap that took millions of years. It didn’t suddenly appear; it went along with the other changes that led to the emergence of homo sapiens.
Even if for some reasons, your transparent people just became transparent at the snap of a finger, scientists will have definitely studied the bio-mechanisms that allow their bodies to be transparent. From there, they have been able to mimic this property and produce transparent GMOs for your people to eat.
You don’t need transparent food
You could have other mechanisms to avoid showing the content of your guts. For example, if evolution led to animals becoming transparent, it would make sense that they also evolved other traits to help them actually be transparent. As such, those animals have a much faster digestion system; in the wild, they hide to eat and digest everything in about 10 minutes and poop out the rest. Once they are done, they can come out of hiding and comfortably be transparent again. Your humans would just have to eat their tacos in private and wait 10 minutes before they are socially acceptable again.
Clothes?
Humans have already come up with a strategy to cover parts of their bodies they don't want everybody to see. Clothing. Just don't go to your restaurant naked (transparent is not invisible by the way, so if showing your genitalia is still awkward in your world, you're gonna need pants. And invisible or not, it's kind of awkward to rub your genitalia on the same chair as everyone else, no?) 335