Anything you’re allergic to or intolerant of
Anything that you’re ethically or morally opposed to consuming
Anything that you don’t like
And that’s it!
No foods are inherently good or bad for you. Believing that can be difficult thanks to conditioning from diet culture or our upbringing, but it is true. The only things to avoid are those that our bodies genuinely can’t handle, or we don’t enjoy.
It is advisable to eat a nutrient-dense diet which offers a balance of macronutrients (yes, including carbs!), as well as ensuring that you remain well-hydrated and don’t rely on caffeine and alcohol to function. But it honestly can be that simple.
If you’d like advice on nutrition, I’m not qualified to help you any further than that (nutrition isn’t the main focus of personal training qualifications, which surprises a lot of people), and if you are concerned then you should speak to your doctor or a qualified nutritionist. The right kind of help and advice could change your life for the better.