i am a traditional naturoopath, in practice for 30 years. i learned simple basic naturopathic principles to begin with and thats what i teach.
for people who feel ill if they don't eat: classical naturopathy calls it a detox reaction-- the body gets a chance to do housekeeping when it doesn't have to digest-digest-digest as usual and you get those headaches, nausea, etc.
the answer is to cleanse, and i'm not talking go out and buy something expensive and hyped-up in a box. go slow and take some time-- have raw vegan days, have some raw juices days, lots of salad, learn food combining, use flaxseed as a colon aid, learn about colon cleansing.
there are many simple safe and cheap basic practices that over time bring about healthful changes. cleansing/detox is the foundation of build a strong vital force to overcome those other conditions.