pam:

You are correct that what a food doesn't contain is a greater determinant of consumption than what it does contain.  However, that still doesn't make the food itself "rewarding", or less so.

First, because "reward" is a mashing together of two distinct phenomena: hedonic impact ("palatability") and incentive salience (our "want" for more).

More importantly, because the lack of nutrition doesn't usually make a food taste better!  What the lack of nutrition does is remove a food's ability to produce satiation and satiety.  

Let's return to the classic prime rib vs. Pringles example: prime rib tastes better (it has more hedonic impact) than Pringles.  However, the prime rib contains lots of complete protein, saturated and monounsaturated fats, fat-soluble vitamins, and other nutrients...and complete protein, in particular, is a strong driver of satiation (and, in the future, satiety).  Therefore, we stop eating the prime rib at some point.

In contrast, Pringles are made of nutrient-free refined "vegetable oil" (mostly linoleic acid, for which our bodies have essentially zero use), and a little bit of potato slurry, which is mostly empty starch calories.  They contain a negligible amount of complete protein, and almost nothing in the way of necessary nutrients.  (Also, linoleic acid somewhat disrupts hunger signaling by itself.)  Result: no matter how many Pringles you eat, your body will not get the nutrition it needs to get you through the day -- and the Pringles do not satiate you (or produce satiety).

This is why "food reward" is a useless and misleading concept: in order to explain consumption of (for example) Pringles over prime rib, we have to posit that Pringles have a magical property called "reward" that makes us eat them to excess -- even when we don't like them as much as other foods!  

In contrast, the real science of hunger lets us understand that Pringles indeed have less hedonic impact than prime rib.  However, because they don't contain the nutrients we need to live, they produce far less satiation (and subsequent satiety), which is why we have such difficulty putting down the tube.  

Hedonic impact can help explain why we start eating a food -- but the determinant of consumption is when we stop eating, which is determined by satiation and our current state of satiety.  

And the primary reason that foods don't produce satiation and satiety is because of what they don't contain (as you correctly infer), rather than what they do.

Otherworld:

Fascinating!  

Hair is an interesting case: it grows on a multi-year cycle, and the follicle has to hit the appropriate phase of its life cycle before new hair can grow.  So I suspect a combination of factors: a threshold effect, where your thyroid status had to normalize sufficiently before hair was able to grow again, and the hair itself having to reach the growth phase.

pam:

I suspect there were a lot of non-believers in the Church during medieval times, since (in Europe) it was the only place where reading and writing were taught.  If you were smart, it was basically your only career choice AFAIK.

JS

pam:

You're still stuck with the naive model as your mental framework.

Here's an analogy: it's not possible to create any of the primary colors (red, green, blue) by the additive mixing of any number of other colors.  No matter how many other colors of light you mix together, you will never produce red light.

Similarly, it's not possible to define or describe precisely defined first-order causes (hedonic impact, incentive salience, satiation, satiety) in terms of imprecisely-defined second-order effects ("rewarding", "hyper-palatable").  No matter how you swizzle these imprecise, second-order terms around, you will never produce a definition of how hunger works.  Consequently, you'll never understand it.

What you need to do is understand the four basic motivations (hedonic impact, incentive salience, satiation, satiety) -- and then define these second-order effects ("unsatisfying, yet rewarding and hyperpalatable") in terms of the four basic motivations.

It's unfortunate that others have confused this issue so deeply by failing to start with well-understood, uncontroversial basic research and terminology.  As I'm sure I've said before, my intent is not to propose Bold New Hypotheses: I view the existing body of well-established science as perfectly adequate to explain observed phenomena, and my intent is to bring that science to my readers as best I can.

Back to your example: greens don't have much hedonic impact by themselves (they're "unpalatable") because they contain essentially zero calories -- and we need macronutrients (protein, fat, carbohydrate) as well as micronutrients.  Furthermore, plants generally contain some quantity of anti-nutrients (e.g. polyphenols), which perhaps have hormetic benefit at low doses, but become frankly toxic at higher doses.  There's a reason that we often find a small amount of bitterness to be tasty and piquant, but a large amount to be disgusting.

Furthermore, we require some quantity of fat to absorb fat-soluble nutrients, which is most likely why we find fats and oils on vegetables so tasty! 

Again, "rewarding" is a meaningless term by itself, because it's a mashing together of the subjective properties of hedonic impact and incentive salience.  If we find a food "rewarding", it's because it has some quantity of hedonic impact (enough to make us start eating it) but produces very little satiation or satiety (so there's very little to make us stop eating it).  And as I explain in the speech, availability modulates the end result.

So we can explain the "binging on stale Wheat Thins" phenomenon this way:

Stale Wheat Thins have very little hedonic impact.  

But, since they're a packaged food and the box is already open (which is why it's stale), they are far more available than an omelet, which requires getting out the frying pan, heating it up, cooking eggs, chopping vegetables, cleaning up, etc.  In contrast, all we have to do in order to eat the Wheat Thins is open the pantry and grab the box.

The problem is this: once we start eating the stale Wheat Thins, it's difficult to stop...because if we are hungry enough that stale Wheat Thins have any hedonic impact at all (remember: hedonic impact is a subjective property based on our current state of satiation and satiety), stale Wheat Thins are not going to satisfy our hunger!  Since they're basically a bunch of empty carbohydrate calories, linoleic acid, and a tiny bit of incomplete, poorly digestible protein, they produce almost zero satiation or satiety.

Then, since the availability of an open box of Wheat Thins in our hand is maximum, it's easy to keep eating them even when their hedonic impact is nearly zero (their incentive salience is still enough to keep us eating) -- and since they produce almost zero satiation or satiety, there's nothing to stop us from eating them except the empty box.

JS