Consuming caffeine, artificial sweeteners and such will not kill you or damage your brain. They are just not good for a recovering brain. A single serving of caffeine a day is considered OK. A single serving of alcohol is OK too. There is no reason to consume artificial sweeteners. There are alternatives to HFCS but moderate consumption of HFCS is not going to hurt you. Just don't overdo it. I drink sugar sweetened soda and juices in moderation.

There is no reason to feel "Woe is me. I consumed high fructose corn sweetener." It like getting a good night's sleep. You are better with it. If you don't get a good night's sleep. It does not kill you. You just don't perform as well.