Ed:

Yes, the brain is involved in biochemistry: it's part of most homeostases, because that's why brains exist -- to help coordinate the function of the trillions of cells in a body (human or otherwise) so that they function as an individual, not as an undifferentiated soup of competing cells!  (And lest we forget, the brain and nervous system are made out of cells, too.)

That being said, the trillions of cells in a human (or any other animal) aren't mindless hand-puppets of the hypothalamus, or any other part of the brain: each one has its own energy needs and expresses receptors according to them (e.g.: "insulin resistance", which is usually the result of trillions of muscle and liver cells saying "No thanks, we're full of glycogen already")...not to mention performing its own unique function (e.g. excreting digestive enzymes, conducting nerve signals), excreting its own waste products, etc.

"Do the cellular processes work the same irrespective of signals from the brain?"

Yes and no.  Yes, because each cell is its own little biochemical unit, with its own function.  No, because most cells are responsive in some way to hormones, peptides, and other signaling molecules (including innervation), which the brain is often involved in maintaining the balance of.

We like to think of the body as a car and our brain as the driver.  Unfortunately, it's far more complicated than that!

JS

Edward:

I'm glad you find my explanations helpful!  It's easy to make "Science!" say almost anything we want through selective citation: it's much more difficult to make sure it's useful and relevant to our own lived experience.

I'm curious how you believe I'm "pussy-footing" around addiction.  Addiction lies on a spectrum of behaviors, all mediated by the same brain circuits -- so defining something as "addiction" instead of "normal behavior" is very much a definition of social norms.  For instance, we consider a daily glass of wine with dinner to be normal behavior, but we do consider daily usage of cocaine to be "addiction".  However, if you're in the Peruvian Andes, however, daily chewing of coca leaves is normal behavior!  And so on.  

Basically, once your habit starts to impact your ability to conform to local norms of behavior, we start calling it "addiction".  

Another example: continual hand-washing and hand-sanitizing was considered OCD twenty years ago: now wet-wipes and buckets of Purell are everywhere, and their use is strongly encouraged!

If that's pussy-footing, then I guess I need to understand how and why.

JS

Susan:

We get hungry every day primarily because there are many nutrients our body can't store.

Protein is the most obvious: we need a certain amount of complete protein each day, or we'll start cannibalizing our own muscle mass to get it.  Many vitamins and minerals (such as Vitamin C, AFAIK) are not stored either, and we must consume them regularly in order to maintain health.  And we have a very limited facility for storing carbohydrate...perhaps 50-100g in the liver, which must power both the brain and our red blood cells (among others), and which must be continually replenished somehow.  (If you eat nothing, it will be replenished via breaking down muscles for protein and turning them into glucose via gluconeogenesis.)  People on hunger strikes die of muscle wasting and lean tissue atrophy long before they run out of body fat.

So even if we have plenty of calories available, in the form of body fat, we still have not decreased our requirements for protein and many micronutrients.

Does this help?

JS

Susan:

Your body's micronutrient needs don't decrease with caloric intake (as a rule)...if you're eating 1200 calories instead of 1800, that doesn't mean you magically need less vitamins or minerals!  Therefore, you'll have to eat far more nutrient-dense foods when trying to lose weight.

And yes, cravings for real foods can result from a need for micronutrients.  For instance, my cravings for seaweed-wrapped sushi handrolls decreased dramatically when I started supplementing iodine.

JS