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Hedonic Impact (“Liking”), Incentive Salience (“Wanting”), and “Food Reward”: Why Are We Hungry? Part VI

Caution: contains SCIENCE!

Now we enter the heretofore-murky waters of liking, wanting, and “food reward”.

(Part VI of a series. Go back to Part I, Part II, Part III, Part IV, or Part V—or go on to Part VII.)

Summary: The Story Thus Far

In previous installments, we’ve established the following:

  • Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.
  • In a properly functioning human animal, likes and wants coincide; satiation is an accurate predictor of satiety; and the combination of hunger signals (likes and wants) and satisfaction signals (satiation and satiety) results in energy and nutrient balance at a healthy weight and body composition.
  • Restrained eating requires the exercise of willpower to override likes, wants, and the lack of satiation or satiety; the exercise of willpower uses energy and causes stress; and stress makes you eat more. Therefore, a successful diet must minimize the role of willpower.
  • A lack of satiety will leave us hungry no matter what else we do to compensate. We fail to achieve satiety by not ingesting (or not absorbing) the energy and/or nutrients our body requires, and by an inability to retrieve the energy and/or nutrients our bodies have stored due to mitochondrial dysfunction.
  • Satiation is an estimate of future satiety based on sensory input. As with satiety, we fail to achieve it by not satisfying our nutritional needs. We can also bypass satiation by decreasing sensory exposure to our foods. Some common enablers are eating quickly, eating while distracted or on the run, and eating calorie-dense packaged and prepared foods.

A Disclaimer

I’ve put off writing these next few articles because they’re likely to cause some controversy, which I don’t enjoy. My objective with the articles I write here at gnolls.org is to organize, distill, and summarize the bewildering variety of nutritional information into succinct, helpful articles, to share them with my readers, and to improve them as new information comes to my attention.

(An aside: I thank you, my readers, for continuing to provide references, intriguing leads, and constructive criticism. Please continue to do so.)

Please note that I have no horse in any of the current races: I am neither selling diet books nor defending a career-building hypothesis, and my current series of articles started long before the AHS and any still-simmering disputes.

Finally, and most importantly, I am not proposing any new theories of hunger or obesity. The current literature is both comprehensive and, I believe, more than adequate to explain and understand observed phenomena.

That being said: let’s get started!

Endless Arguments Are Often A Sign Of Murky Definitions

When, after innumerable posts and presentations on the subject, we see very smart people unable to articulate exactly what is meant by fundamental concepts like “palatability”, it’s quite likely that the hypothesis in question is poorly specified.

Therefore, I will briefly summarize the current state of scientific knowledge, as I understand it, on the subject of hunger and reward.

Defining Our Terms: “Liking” = Hedonic Impact, “Wanting” = Incentive Salience

Though the terms “liking” and “wanting” seem reasonably self-explanatory, we must be careful when using them in the scientific sense.

When we speak of “liking” something, we’re consciously predicting our future reactions. (“I like eggs.”) However, in the scientific literature, “liking” refers only to our actual reactions of pleasure, both conscious and unconscious—the hedonic impact of an experience.

Similarly, when we speak of “wanting”, we’re consciously predicting our future likelihood of seeking out an experience. But again, in the scientific literature, “wanting” refers only to our actual motivation to do so—the incentive salience of an experience.

Curr Opin Pharmacol. 2009 Feb;9(1):65-73. Epub 2009 Jan 21.
Dissecting components of reward: ‘liking’, ‘wanting’, and learning.
Berridge KC, Robinson TE, Aldridge JW.
[Note: free full text]

In recent years significant progress has been made delineating the psychological components of reward and their underlying neural mechanisms. Here we briefly highlight findings on three dissociable psychological components of reward: ‘liking’ (hedonic impact), ‘wanting’ (incentive salience), and learning (predictive associations and cognitions).

The concept of “palatability” can be understood as the hedonic reward of food:

For most people a ‘reward’ is something desired because it produces a conscious experience of pleasure — and thus the term may be used to refer to the psychological and neurobiological events that produce subjective pleasure. But evidence suggests that subjective pleasure is but one component of reward, and that rewards may influence behavior even in the absence of being consciously aware of them. Indeed, introspection can actually sometimes lead to confusion about the extent to which rewards are liked, whereas immediate reactions may be more accurate [1]. In the extreme, even unconscious or implicit ‘liking’ reactions to hedonic stimuli can be measured in behavior or physiology without conscious feelings of pleasure (e.g. after a subliminally brief display of a happy facial expression or a very low dose of intravenous cocaine) [2,3].
Ibid.

And when most of us think of “food reward”, we are thinking purely of “wanting”—specifically “incentive salience”:

By ‘wanting’, we mean incentive salience, a type of incentive motivation that promotes approach toward and consumption of rewards, and which has distinct psychological and neurobiological features. For example, incentive salience is distinguishable from more cognitive forms of desire meant by the ordinary word, wanting, that involve declarative goals or explicit expectations of future outcomes, and which are largely mediated by cortical circuits [34–37].

By comparison, incentive salience is mediated by more subcortically weighted neural systems that include mesolimbic dopamine projections, does not require elaborate cognitive expectations and is focused more directly on reward-related stimuli [34,35,38]. In cases such as addiction, involving incentive-sensitization, the difference between incentive salience and more cognitive desires can sometimes lead to what could be called irrational ‘wanting’: that is, a ‘want’ for what is not cognitively wanted, caused by excessive incentive salience [39•,40•,41]. [emphasis mine]
Ibid.

That explains quite a bit right there, doesn’t it?

I’d love to quote more of Berridge et.al.—but as the full text is available for free, I’ll just recommend that you read it if you’re interested in digging into the details.

It should now be clear that “food reward” has three distinct components which we must distinguish and define if we hope to understand it:

  • The hedonic impact of eating food: its palatability.
  • Incentive salience: the drive to consume more food.
  • The process of learning, in which both hedonic impact and incentive salience are modified by experience.

If we fail to separate these components, we find ourselves creating tautologies. For example, it’s obviously absurd to say alcoholism is caused by “alcohol reward”—but if we distinguish the hedonic impact of alcohol from the incentive salience of alcohol, suddenly we have a handle by which to grasp the issues and make headway.

Intermission

Some Important Observations About Liking, Wanting, and Learning

Here are what I believe are some important takeaways from the literature as they apply to hunger:

  • Reward is not a concept limited to food. Common sources of reward in everyday life also include social approval from parents, friends, co-workers, and strangers; legal and illegal drugs; physical activities, such as recreational sports; successful accomplishment of tasks; and media consumption, including television and the Internet. Anything we “like”—anything with hedonic impact—is capable of creating and reinforcing a “want” for more—incentive salience.
        In fact, much of the literature studies drug reward (legal and illegal). These are easier cases to study, since the human body has no nutritional requirement for nicotine, alcohol, or cocaine, and reward is not tied up with other motivations.
  • Taste is not the only determinant of hedonic impact. The circumstances surrounding consumption, such as social approval, are also powerful determinants…and they don’t even have to be associated with consumption!
        For example, beer is generally an acquired taste: most of us instinctively dislike its bitterness, and only ‘develop a taste’ for beer as we associate beer drinking with intoxication and positive social interactions. Note the universal context of beer commercials: beer = fun times with friends. Also note that advertising can drive consumption, despite having no association with the actual action of consumption.
        Another example: many Muslims and Jews are repulsed by even the thought of pork purely due to social context, despite having no intrinsic inability to ingest or digest it.
  • Incentive salience (“wanting”) is not an intrinsic property of food, or anything else. Unlike our instinctive aversion to spiders, humans have no instinctual knowledge of Pringles, Twizzlers, or Cinnabons. Incentive salience is a learned property.
  • Therefore, incentive salience (“wanting”) is not a static property. It is created and reinforced by the hedonic impact (“liking”) of food consumption itself, by the positive experiences of satiation and satiety that consumption of nutritious food can produce, and by its associations with other rewarding factors and experiences (as enumerated above).
  • We must distinguish experiences that modify hedonic impact (“liking”) or incentive salience (“wanting”) from incentive salience itself. For instance, the fact that the satiety response can modify incentive salience does not make satiety part of the reward response.
        It’s even easier to understand this error when we understand that social context affects hedonic impact: it’s clearly silly to call social relationships part of “food reward”. This error has been a major source of confusion in the discussion so far.

Conclusion

In order to understand the role of “food reward” in hunger, we must define and distinguish its constituent motivations:

  • The hedonic impact of eating food: its palatability.
  • Incentive salience: the drive to consume more food.
  • The process of learning, in which both hedonic impact and incentive salience are modified by experience.

Further, we must understand that reward is not limited to food, is neither static nor an intrinsic property of the food itself, and is modified by many experiences besides its taste during the act of consumption—most of which are not themselves reward pathways.

We’ll start exploring these motivations and interactions—and how they fail—in Part VII. Click here to keep reading!

Live in freedom, live in beauty.

JS

(Part VI of a series. Go back to Part I, Part II, Part III, Part IV, or Part V—or go on to Part VII.)


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Why Are We Hungry? Part II: Hunger Is The Product Of Multiple Perceptions And Motivations, Sometimes Conflicting

Caution: contains SCIENCE!

Part I of this series clearly establishes the following, which I hope is non-controversial:

Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.

This is intuitively obvious to everyone: hunger is not a generic drive, satisfiable by shoving a generic substance called “food” into our mouths. The fantasy of “food pills” remains squarely in the Future That Never Was, along with flying cars and nuclear power too cheap to meter.

City of the Future

I miss the future that never was.

While a bewildering variety of “meal replacement drinks” exists, walking down any commercial street in the world reveals restaurants—not kiosks with a row of Slurpee machines filled with flavors of Ensure, Slim-Fast, and Muscle Milk. And even the most dispiriting accretion of fast-food dispensaries around a freeway exit features everything from hamburgers to burritos to chicken salads to tuna sandwiches.

Fortunately, it’s possible to cut through the fog of conflicting motivations by analyzing these four drives in detail: “liking” and “wanting”, which make us eat, and “satiation” and “satiety”, which make us stop eating.

First, let’s define the four drives. I’ll start with the end of the process, for reasons that will become clear.

What Is Satiety? What Does “Sated” Mean?

“Satiety” is our body’s response to the absorption of nutrients through the intestine.

Nutrition Bulletin Volume 34, Issue 2, pages 126–173, June 2009
Satiation, satiety and their effects on eating behaviour
B. Benelam

When nutrients reach the intestine and are absorbed, a number of hormonal signals that are again integrated in the brain to induce satiety are released.

The important takeaway here is twofold. First, satiety is not a conscious response over which we have any control. Satiety is our body’s direct measurement of actual nutrient intake—a system honed over hundreds of millions of years of evolution. It answers the question “Should I seek out food now—or can I do something else, like seek a mate, play with my children, or take a nap?”

Second, since satiety is based on actual nutrient absorption, which occurs through the small intestine, it takes a long time to receive any satiety cues from the food we eat. As I describe in this article, it takes 2.5-3 hours before half of a mixed meal has even left the stomach, much less been absorbed through the intestine! GI transit times vary dramatically, and are shorter for highly processed, fat-free foods—but it’s clear that satiety takes far too long for it to be a useful signal to stop eating.

Most likely this is why satiation is a separate biochemical process.

What Is Satiation? What Does “Satiated” Mean?

Satiation occurs when the value we place on another bite of food drops below zero. It is our estimate of the marginal utility of eating the next piece of food.

For those not familiar with the economic term, “marginal utility” refers to the value we place on acquiring one more of something. “Marginal” means that we may already have some of it, i.e. we may not be starting from zero. Furthermore, the concept of “diminishing marginal utility” is often useful, because the value we place on something usually decreases as we accumulate more of it. (There are exceptions, which we’ll discuss later.)

This is easy to demonstrate: imagine that we’re at a big outdoor concert, like Coachella. It’s very hot outside, we’re thirsty from standing in the sun and shouting along to bands we like, it would take us a long time to get out to the car and back in, and we don’t want to miss the next band. A cold bottle of water might be worth $5 to us at that point, or even more…so we willingly pay the extortionate $4 from the kiosk. Once we drink it, though, we’re no longer as thirsty as we were, so the value we place on a second bottle might be only $2. However, since the venue still charges $4, we don’t buy a second bottle. In other words, a transaction only occurs if the value we place on something is greater than or equal to the price at which it’s available.

It’s easy to understand satiation by going to an all-you-can-eat buffet: the value we place on each additional plate of food decreases until we decide it’s not even worth getting up from the table to take more—though we could have it for free!

Satiation is not the same thing as being full, or being sated. If all we have in the house is a jar of sweet pickles and a bag of Twizzlers, we might quickly become satiated, since we don’t want to eat any more of either. However, this does not leave us sated: our body knows that pickles and Twizzlers do not contain the nutrients we need to live.

The important distinction here is that satiation is an estimate, based on the sensory experience of eating. Ideally, satiation would accurately predict future satiety—but while satiety is a direct measurement of nutrient intake, and cannot be easily fooled, satiation is dependent on our perceptions.

You Can Fake Satiation, But You Can’t Fake Satiety

Satiation is affected by our senses of taste, smell, texture, and stomach distention; it’s affected by our perception of a food’s caloric and nutritional value; and it’s even affected by mundane considerations like serving size. Not only can satiation be overridden by sufficiently powerful wants, our perceptions of satiation (= future satiety) can easily be influenced or fooled entirely.

Signals about the ingestion of energy feed into specific areas of the brain that are involved in the regulation of energy intake, in response to the sensory and cognitive perceptions of the food or drink consumed, and distension of the stomach.Ibid.

Many different experiments prove that satiation can be manipulated: here are a couple I found interesting. Let me know if you find others!

J. Nutr. February 2009 vol. 139 no. 2 394-399
Hidden Fat Facilitates Passive Overconsumption
Mirre Viskaal-van Dongen, Cees de Graaf, Els Siebelink, and Frans J. Kok

“In the presence of visible fats, energy intake was lower than in the presence of hidden fats, suggesting that hidden fats may contribute to overconsumption.”

The effect was minor but significant: 8-9%. Our perceptions do not perfectly estimate the nutritive content of foods.

Am J Clin Nutr August 2009 vol. 90 no. 2 269-275
Effect of bite size and oral processing time of a semisolid food on satiation
Nicolien Zijlstra, René de Wijk, Monica Mars, Annette Stafleu, and Cees de Graaf

“Conclusion: This study shows that greater oral sensory exposure to a product, by eating with small bite sizes rather than with large bite sizes and increasing OPT [oral processing time], significantly decreases food intake.”

The effect was striking: people ate up to 50% more when able to eat freely vs. when limited to small bites every nine seconds! Therefore, satiation is also affected by how fast we eat and how big of a bite we take. The old advice to “eat slowly and mindfully” and “take small bites” does have some scientific support.

The study also contains this hidden gem: “The subjects had to be healthy, be aged 18–30 y, be of normal weight [body mass index (in kg/m2): 18.5–25.0], and like chocolate custard.”

What Is “Liking”? What Are “Likes”?

Psychopharmacology doi:10.1007/s00213-008-1099-6
Affective neuroscience of pleasure: reward in humans and animals
Kent C. Berridge and Morten L. Kringelbach

Liking: the actual pleasure component or hedonic impact of a reward. Pleasure comprises two levels: (1) core ‘liking’ reactions that need not necessarily be conscious; (2) conscious experiences of pleasure…

In common usage, “liking” is the reward we anticipate from future consumption. However, in scientific usage, “liking” refers to the pleasure we feel from actually eating food—its hedonic impact.

Like “satiation”, “liking” is situationally dependent, and it is only nominally under conscious control. Cultural and social conditioning can affect our likes, particularly as children: for instance, most non-Japanese people find natto disgusting, and most non-Filipinos have a difficult time with balut.

BLEEEEAAAAARGH

It reminds me of Giger's "Alien".

Yes, that's a chicken embryo.


And though we cannot simply choose to “like” something, conscious efforts to affect our preferences will sometimes have an effect over time: for instance, most children find beer disgusting, and it’s well-known that most of us must “develop a taste” for it.

It is important to note that palatability is a major component of “liking”, and “hedonic impact” is the technical term for the pleasure associated with actual consumption. However, we must be careful to distinguish the reward itself from our perception of it. When we say we “like” a food, we may also be taking conscious perceptions and biases into account.

Neurosci Biobehav Rev 20(1) 1-25, 1996.
Food reward: Brain substrates of wanting and liking
KC Berridge

Food reward is not simply a physical property of a taste stimulus itself…Palatability, or the hedonic component of food reward, instead results from a central integrative process that can incorporate aspects not only of the taste, but of the physiological state and the individual’s associative history.

What is “Wanting”? What Are “Wants”?

“Wanting: motivation for reward, which includes both (1) incentive salience ‘wanting’ processes that are not necessarily conscious and (2) conscious desires for incentives or cognitive goals.” –Berridge and Kringelbach

Rephrased: Wants are desires at a specific moment in time. We measure them by how motivated we are to actually go out and get whatever it is we ‘want’. Applied to food, we often use the word “appetite”.

Note that wants are partially, but not entirely, under our conscious control. I might know that cake is bad for me, but that doesn’t stop me from wanting cake. Furthermore, wants vary dramatically over time depending on the degree of satiation and satiety we are experiencing. To use my previous example, if I’ve just eaten a 20-ounce prime rib, I’m unlikely to want any more prime rib…but that doesn’t mean I like prime rib any less.

You’ll note that I’m carefully avoiding the gory biochemical details of these sensory and motivational pathways. This is intentional, and it’s for two reasons: first, we don’t completely understand them, and second, they don’t really matter. The details of ghrelin, leptin, cholecystokinin, peptide YY, and the dopamine-reward system are fascinating…but since we’ve already demonstrated that there’s no magic pill we can take that blunts our hunger without making us poop our pants, we don’t have to understand all of the details.

In short, we can understand wanting, liking, satiation, and satiety (and their interactions) on a purely functional level. We don’t have to understand the biochemistry of these drives in order to eat like a predator.

However, if you want to dive in, I recommend turning to chapter 7.3 of the online textbook Endotext, “The Regulation of Food Intake in Humans”. Its authors include several co-authors of papers I’ve cited in this series.

We can relate satiation and wanting in this common-sense way: satiation occurs when we don’t want any more food.

A Summary Of The Components Of Hunger

  • Likes (scientific usage) = the pleasures we experience from eating, known scientifically as “hedonic impact”.
  • Wants = desires at a specific moment. A measure of our motivation to attain a reward. Our “appetite”.
  • Satiation = absence of motivation to eat more. The absence of attainable wants. An estimate of future satiety, based on the sensory experience of eating.
  • Satiety = a signal from your body that it is replete with nutrients.

Perceptions And Motivations In Harmony And In Conflict:
Evolutionary Concordance And Discordance

Ideally, if everything were functioning properly, our likes and wants would always coincide, satiation would always be an accurate predictor of satiety, and the combination of hunger signals (likes and wants) and satisfaction signals (satiation and satiety) would result in energy and nutrient balance.

Existing in this state of harmony and balance would have been strongly selected for throughout tens of millions of years of evolutionary history, all the way back to the great apes and beyond. Any animal whose faulty perceptions and motivations caused it to become obese, emaciated, malnourished, or poisoned by excess would have been strongly selected against.

However, we can see that both the simple states of hunger and non-hunger, in which our motivations agree, are just two possible outcomes of the collision of these four processes—and that just as hunger isn’t necessary to make us eat, non-hunger isn’t sufficient to make us stop eating.

Furthermore, we can see that these disorderly outcomes are most likely the product of evolutionary discordance.

I’ll explore some of those issues in Part III and beyond.

Live in freedom, live in beauty.

JS

Continue to Part III, “Willpower And Why It Fails.” (Or back to Part 1.)


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Why Are We Hungry? Part I: What Is Hunger? Liking Vs. Wanting, Satiation Vs. Satiety

(This is a multi-part series: click here for the index.)

Caution: contains SCIENCE!

It is the 21st century. We have telephones that fit in a watch pocket, we can sequence the genetic code of life itself, and we can sift the accumulated knowledge of centuries in fractions of a second using Internet search engines. Yet we still don’t understand enough about human biochemistry to create a pill that stops us from eating without causing heart valve defects or uncontrollable diarrhea.

Diet pill’s icky side effects keep users honest, msnbc.com, 7/6/2007

“I’ve pooped my pants 3 times today, and sorry to get descriptive but it even leaked onto the couch at one point!”

“Ya know how when you start moving around in the morning ya pass a little gas. Well, I did and then went into the bathroom and to my horror I had an orange river of grease running down my leg.”

Do Diet Drugs Work?, The Telegraph, 4 May 2009

“I’ve done it. I figured out the secret behind the Alli pills. It’s fear…It’s amazing how the thought of suffering faecal incontinence can create rock solid will-power.

Clearly I’m in the wrong business: writing life-changing books and articles about how to stay fit and healthy is far less profitable than selling drugs that make people crap their pants.

Meanwhile, in the absence of the magical anti-hunger pill, everyone seems to have their own concept of how to defeat hunger—and thousands of diet books published every year claim that we are simply deficient in everything from acai berry extract to “resistant starch” to the urine of pregnant women. Obviously this is all baloney, because we’re fatter and sicker than ever…

…so let’s back up a few steps and ask ourselves a simple question: “Why are we hungry?”

To answer this, we need an answer to an even simpler question:

“What is hunger?”

Disassembling Hunger and Appetite

To most dieters, hunger is a crafty, insidious demon whispering sweet nothings in our ears.

"Pringles are delicious, and you can stop eating them any time you want."

Yet much of the published research, and most of the popular discourse, simply dismisses hunger as an annoying inconvenience—an atavistic, mildly embarrassing instinct that we must rise above in order to maintain our health.

This is completely untrue. Hunger is a normal and necessary human drive, and it serves a very important function: to cause us to find and ingest the nutrients we need to survive. Yet to understand hunger, we must break it down into its components, because:

Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.

Until we understand this, we are doomed to perpetual confusion over our own motivations and desires—let alone others’ writings and recommendations on how to successfully deal with them.

I’ve addressed this subject before, in my very popular article Why Snack Food Is Addictive, which (among other things) explains the concept of “food reward”. What I’m doing here is creating a theoretical framework that allows us to go even farther—by understanding the concept of hunger.

Components of Hunger: Liking Vs. Wanting

We know that liking something and wanting something are not the same thing. I like prime rib, but I don’t want any right now, because I just ate.

Miraculously, the scientific literature often uses helpful and descriptive English words when describing components of hunger. “Liking” and “wanting” are part of the official scientific lexicon: “liking” is a measurement of the pleasure we experience upon eating, i.e. palatability, and “wanting” is a measurement of the relative motivation to acquire and ingest a food.

It turns out that “liking” and “wanting” produce specific patterns of activity in the human brain!

Pharmacology Biochemistry and Behavior
Volume 97, Issue 1, November 2010, Pages 34-46
Hedonic and motivational roles of opioids in food reward: Implications for overeating disorders
Susana Peciña and Kyle S. Smith

Food reward can be driven by separable mechanisms of hedonic impact (food ‘liking’) and incentive motivation (food ‘wanting’). Brain mu-opioid systems contribute crucially to both forms of food reward. Yet, opioid signals for food ‘liking’ and ‘wanting’ diverge in anatomical substrates, in pathways connecting these sites, and in the firing profiles of single neurons.

Brain Research Volume 1350, 2 September 2010, Pages 43-64
The tempted brain eats: Pleasure and desire circuits in obesity and eating disorders
Kent C. Berridge, Chao-Yi Ho, Jocelyn M. Richard and Alexandra G. DiFeliceantonio

“Liking” mechanisms include hedonic circuits that connect together cubic-millimeter hotspots in forebrain limbic structures such as nucleus accumbens and ventral pallidum (where opioid/endocannabinoid/orexin signals can amplify sensory pleasure). “Wanting” mechanisms include larger opioid networks in nucleus accumbens, striatum, and amygdala that extend beyond the hedonic hotspots, as well as mesolimbic dopamine systems, and corticolimbic glutamate signals that interact with those systems.

As we’d expect, “liking” tends to stay more stable over time, whereas “wanting” tends to change dynamically, being a measure of one’s desires at that moment:

Physiology & Behavior Volume 90, Issue 1, 30 January 2007, Pages 36-42
Is it possible to dissociate ‘liking’ and ‘wanting’ for foods in humans? A novel experimental procedure
Graham Finlayson, Neil King and John E. Blundell

Findings indicate a state (hungry–satiated)-dependent, partial dissociation between ‘liking’ and ‘wanting’ for generic food categories. In the hungry state, participants ‘wanted’ high-fat savoury > low-fat savoury with no corresponding difference in ‘liking’, and ‘liked’ high-fat sweet > low-fat sweet but did not differ in ‘wanting’ for these foods. In the satiated state, participants ‘liked’, but did not ‘want’, high-fat savoury > low-fat savoury, and ‘wanted’ but did not ‘like’ low-fat sweet > high-fat sweet. More differences in ‘liking’ and ‘wanting’ were observed when hungry than when satiated.

This would indeed seem to be the common-sense result, but it’s important to understand that liking vs. wanting are not just theoretical constructs: they are distinct biochemical processes.

These motivations don’t just apply to food: any experience we “like” is capable of producing a “want” for more. I discuss this at length in Part VIII.

Components of Hunger: Satiation Vs. Satiety

We also know that the factors which make us stop eating (satiation) are different than the factors that cause us to feel hungry or not hungry (satiety). If all I have available to eat is cotton candy, I’ll soon be satiated, with no desire to eat more—but I won’t experience satiety, because I’ll still be hungry for real food.

Like the terms “liking” and “wanting”, “satiation” and “satiety” have specific meanings in the scientific literature, though according to the dictionary they are synonyms.

Interestingly, French distinguishes them in the same way scientists do: “rassasiement” = satiation, “satiété” = satiety.

Also like the terms “liking” and “wanting”, “satiation” and “satiety” are distinct and reproducible drives:

Nutrition Bulletin Volume 34, Issue 2, pages 126–173, June 2009
Satiation, satiety and their effects on eating behaviour
B. Benelam

Satiation and satiety are controlled by a cascade of factors that begin when a food or drink is consumed and continues as it enters the gastrointestinal tract and is digested and absorbed. Signals about the ingestion of energy feed into specific areas of the brain that are involved in the regulation of energy intake, in response to the sensory and cognitive perceptions of the food or drink consumed, and distension of the stomach. These signals are integrated by the brain, and satiation is stimulated. When nutrients reach the intestine and are absorbed, a number of hormonal signals that are again integrated in the brain to induce satiety are released.

Physiol Behav. 1999 Jun;66(4):681-8.
Palatability affects satiation but not satiety
De Graaf C, De Jong LS, Lambers AC.

The results showed that the ad lib intakes of the less pleasant and unpleasant soups were about 65 and 40% of the intake of the pleasant soup. Subjects ingested about 20% more soup when the subjects had to wait for the test meal about 90 min, compared to the 15 min IMI condition. The availability of other foods had no effect on the effect of pleasantness on ad lib intake. There was also no effect of the pleasantness on subsequent satiety: hunger ratings and test meal intake were similar after the three standardized soups. One conclusion is that pleasantness of foods has an effect on satiation but not on subsequent satiety.

This is another common-sense result: we might eat less of unpalatable foods, but having eaten less, we’re more hungry afterward. And once again, we find that the motivation to stop eating (satiation) is a distinct biochemical process from the satiety (or lack thereof) we feel later on.

Conclusion

Hunger is the interaction of several different clinically measurable, provably distinct biochemical processes—each with its own effects on our brains and bodies. Until we understand this, we are doomed to confusion: fragmentary understanding and incomplete solutions that address only one component of hunger while ignoring the others.

Fortunately, we don’t have to understand the biochemical cascades involved in liking, wanting, satiation, and satiety—because no one does. (These are “active research areas”, which means “we’re still trying to figure all this stuff out”.) Simply understanding these drives on a conceptual level—and why they were selected for in our evolution as humans—can help us navigate the dangerous shoals of dietary advice.

I’ll explore some of these questions in more detail in the upcoming weeks.

Live in freedom, live in beauty.

JS

Continue to Part II, “Hunger Is the Product Of Multiple Perceptions And Motivations, Sometimes Conflicting.”


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