If you ever heard about Maslow hierarchy, the status is way towards the top. Things like hunger, safety and not being in pain is much lower. So I highly doubt many people would forgo food and agree to be in constant excruciating pain just to be able to access facebook.
Have you ever met a nutrient deficient heroin, crack or meth addict? I'd be willing to bet those habits are closer to the top than food, but they seem to forego it and take that as far as they can without dying. We are talking about addiction here after all.
Those are physiological addictions that literally rewire your body chemistry and how your brain perceives reality. There's addiction and there's addiction.
What do you think happens to you when you love, when you hate, when you feel rejected, appreciated, embraced, venerated, when you feel like you're being venerated without effort, you may feel like you're cheating and get a rise of it, or feel guilty from it, but in every case there's an endocrine response.
All of these chemical pathways are triggered by the hollow nonexistent social interactions, it can be an emotional rollercoaster and at the core is stimulation by endogenous compounds that can also be chemically addictive. You're finding a distinction that simply isn't there.
I dare you to show me any mention in the scientific literature of a physiological addiction to facebook comparable to opioid or alcohol dependency. A reductionist approach of "everything in a body is chemistry" does not mean all chemistry is alike. Normal emotions to not create the same long-term effects in body's neurochemistry as things like opioids do. That's why people take them - you can't really just get rid of an excruciating pain by thinking about something fun. You can by taking drugs, because drugs meddle with the body chemistry in a much stronger way than the normal endocrine response does. That meddling has a bad side - since it's so much stronger and invasive, it creates permanent damage. Looking at cats on facebook also causes chemical reactions, but not nearly as strong as the drugs do.
I think more reasonable stance would be that addicted people stop caring about what they eat, and prioritize time spent on Facebook instead of time spent on cooking better food.