I can't touch caffeine.
I used to drink coffee with no effect, I could drink it before bed and sleep fine. Occasionally, If I was tired at work I would drink 1 energy drink (this was not often though maybe 5 times in as many years.)
When I was really trying lose weight for sport, I'd drink caffeine (insert brand) before going to training after work just to give me the motivation. I would drive a long way in the day and work hard.. Then physically train hard most days of the week and was full on at the weekend. The body had not issue with it.
I can't touch booze now either (even though I used to like to go out and have drink). A sip or a mouthful can make me feel like achy and hot when I wake up. It's 99.9% certain within a day or so I will feel like have symptoms like a bad cold (without the running nose or sneezing). I will say I feel like I am getting the flu. It can also make me feel more down...
I never suffered any anxiety or anything like depression before I got cfs/me. It has taken many years for me to start feeling different mentally, I think this is natural too. It's a complete life change and my brain cells feel like they are dying... I loved my work and activity level before.
I think my CFS/ME is very much linked to stress, so no surprise anything that places stress on the body makes it worse.. I can go from being functional tired, to semi housebound by consuming the wrong things.
Large meals and regular junk food also make me ache and feel hot... Again as a Neutritionist explained, it takes energy for the body to breakdown food, and lots of bad food can give a kind of food hangover. Best practice was to eat small meals regular, pick foods that were better in nutritional value, so supporting the body rather than trashing it.
Obviously not everyone is the same, but I bet the advice is fairly generic for anyone who is poorly.
Eating healthy and taking supplements for me, enables me to have a fairly normal life, the over doing it, is what messes me up, then I use junk food as a pick me up and it starts a whole cycle, perhaps similar to drinking booze to mask a problem, and hi energy bad food seems to reward the brain with feel good chemicals, followed by feel crap..so eat more.
I also think too much bread might be bad for me. I feel better when eating a certain way, but it's hard to live long term (restricted) like an athlete when you're just doing it to get by each day and still don't feel great.
Excuse bad writing... tired
Sorry I digress, personal experience.