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When Satiation Fails: Calorie Density, Oral Processing Time, and Rice Cakes vs. Prime Rib (Why Are We Hungry? Part V)

Caution: contains SCIENCE!

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

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 vs. Satiety, Satiated vs. Sated: Understanding The Differences

In common use, “satiation” and “satiety” are basically synonyms. Even the scientific literature does not always maintain or respect the difference, so it’s important to understand and distinguish exactly what’s being discussed.

Satiety is your body’s response to the availability of nutrients from food that you’ve already digested and processed. (We discussed satiety at length in Part IV.)

Satiation is your immediate reaction to the ingestion of food—the drive that causes you to stop eating. It is your body’s attempt to estimate future satiety via sensory input: smell, taste, texture, and stomach distention.

I’ve quoted this passage before, but I’ll quote it again, because it’s important:

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

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.

It’s difficult to draw a sharp line between satiation and satiety: some foods digest very quickly, and their nutrients are available quickly enough for satiety to affect the satiation response. (Example: simple sugars and carbohydrates, whey protein isolate.) And there is strong support for the idea that taking longer to eat results in lower food intake, probably because the satiety response begins to come into play.

Satiation Is Relative To Satiety

Since satiation is an attempt to predict (via sensory input) future satiety (i.e. nutrient absorption), it should be obvious that our current state of satiety affects what foods we find satiating—or not satiating. Here’s an interesting example of this effect:

J. Nutr. January 1, 1998 vol. 128 no. 1 61-67
Prior Day’s Intake Has Macronutrient-Specific Delayed Negative Feedback Effects on the Spontaneous Food Intake of Free-Living Humans
John M. de Castro

Food energy intake during a day was found to only mildly affect intake on the subsequent day (mean r = −0.07, P < 0.001), but was more strongly negatively related to intake occurring on the second (mean r = −0.18, P < 0.001) and third day (mean r = −0.10, P < 0.001) afterward.

Each macronutrient was shown to have a maximal negative relationship with subsequent intake of that same macronutrient, with 2-d lag mean autocorrelations equal to −0.11, P < 0.001 for carbohydrate, equal to −0.18, P < 0.001 for fat, and equal to −0.13, P < 0.001 for protein. These effects on daily intake were found to result from separate negative feedback effects on meal size and frequency.

Stated plainly: not only does eating more food cause you to eat less food 2-3 days afterward—eating more protein, fat, or carbohydrate causes you to eat less of the same 2-3 days afterward. Here are the graphs:

The effect is not large, but it is consistent and significant.

And though deCastro didn’t graph meal size and frequency, they were also compensated for with a 2-3 day time lag.

There are some studies that claim to show macronutrient compensation doesn’t exist—but they examine only the next meal eaten on the same day, or perhaps the morning after.

This is only one example of satiety affecting satiation, but I think it proves the point: satiation is relative to your current state of satiety. (For another real-world example of the effects of previous meals on satiety, see the study referenced in my classic article How “Heart-Healthy Whole Grains” Make Us Fat.)

We’re all familiar with the manifestations of this effect. For instance, after two weeks of living primarily on bento boxes and bowls of ramen while in Japan, my friend and I found ourselves absolutely craving red meat—and we proceeded to draw a crowd of spectators at an all-you-can-eat yakiniku restaurant, by eating more than any of them had probably seen consumed at once by anyone but a sumo wrestler.

Yakiniku = grill your own meat, at your own table. Basically Korean BBQ without the kimchi.


How Satiation Fails: Bypassing Sensory Input

Since satiation is dependent on sensory input, it seems logical that we can break satiation by bypassing or attenuating the sensory experience of eating.

This is, in fact, the case.

It has been known for a long time that the obese eat more quickly than the non-obese:

Int J Obes. 1977;1(1):89-101.
Eating in public places: a review of reports of the direct observation of eating behavior.
Stunkard A, Kaplan D.

…Two measures showed promise in discriminating obese from non-obese persons. The first was food choice: obese persons chose more food than non-obese persons (and men chose more than women and tall persons more than short ones). The second measure was rate of eating: obese persons consumed more food per minute than non-obese persons.

Further reading: Psychosom Med Vol. 42, No. 6
Eating Style of Obese and Nonobese Males
Kaplan D

And under controlled conditions, people eat more when they are allowed to eat quickly than when their eating rate is restricted:

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

Results: Subjects consumed significantly more when bite sizes were large than when they were small (bite size effect: P < 0.0001) and when OPT [oral processing time] was 3 s rather than 9 s (OPT effect: P = 0.008). Under small bite size conditions, mean (±SD) ad libitum intakes were 382 ± 197 g (3-s OPT) and 313 ± 170 g (9-s OPT). Under large bite size conditions, ad libitum intakes were much higher: 476 ± 176 g (3-s OPT) and 432 ± 163 g (9-s OPT). Intakes during the free bite size conditions were 462 ± 211 g (free OPT), 455 ± 197 g (3-s OPT), and 443 ± 202 g (9-s OPT).

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, significantly decreases food intake.

Many food choices can increase our rate of eating. We can eat liquid foods more quickly than solid foods, soft foods more quickly than hard foods, tender foods more quickly than tough foods.

For instance, “meal replacement shakes”, being liquid, don’t produce the same satiation response as eating real food:

Journal of Comparative and Physiological Psychology Volume 68, Issue 3, July 1969, Pages 327-333 doi:10.1037/h0027518
Preloading and the regulation of food intake in man
Barbara C. Walikea, Henry A. Jordan and Eliot Stellar

“17 human Ss [Ss = subjects] ate 20-min meals of Metrecal through a straw connected to a hidden reservoir. Oral preloads of Metrecal were administered before the meals, and these varied 20-120% of the amount of the base-line meal intake and were given 1-120 min. before the meal. Test-meal intake was depressed as a function of the size of the preload; however, the Ss did not take the preload fully into account and they overate.

Note: Metrecal started the 1960s craze for meal replacement shakes. Its ingredients: “A mix of skim-milk powder, soybean flour, corn oil, minerals and vitamins.” (More information here.) It is also claimed that Metrecal tasted absolutely terrible—though since it hasn’t been produced since the 1970s, there’s no way to know for sure.

And people eat more yogurt when they can suck it through a straw than when they have to use a spoon:

Am J Clin Nutr April 2010 vol. 91 no. 4 841-847
Intake during repeated exposure to low- and high-energy-dense yogurts by different means of consumption
Pleunie S Hogenkamp, Monica Mars, Annette Stafleu, and Cees de Graaf

Results: Intakes (P = 0.01) and eating rates (P = 0.01) were highest in the liquid/straw group. Average intakes over 10 exposures were 575 ± 260 g for liquid/straw, 475 ± 192 g for liquid/spoon, and 470 ± 223 g for semisolid/spoon; average eating rates were 132 ± 83 g/min for liquid/straw, 106 ± 53 g/min for liquid/spoon, and 105 ± 88 g/min for semisolid/spoon.

Conclusions: We observed no energy intake compensation after repeated exposure to yogurt products. Differences in ad libitum yogurt intake could be explained by eating rate, which was affected by the different means of consumption.

From this, we can see that it’s easy to bypass our satiation response by eating highly processed foods. Processing (and cooking) basically pre-digests food for us, which increases both the speed at which we can eat it and the speed at which we can absorb it.

Even the toughest, stringiest cut of modern beef is from an animal that has never had to run from predators…and it’s been ‘aged’ for at least two weeks, which is to say that it’s been left to slowly rot in its own digestive enzymes in order to make it softer and more tender.

Thought experiment: consider the rate at which you could hack meat and fat off of a fresh bison carcass using sharp rocks, and the rate at which you could chew and swallow that raw meat—versus the speed at which you can gobble down medium-rare hamburger or prime rib.

Finally, I’ll note that an increasing cultural tendency to “eat on the run” increases our rate of food ingestion. Gobbling down food in a hurry because we need to get back to work, or pick up the kids, or get our shopping done, seems likely to cause us to eat more regardless of what we’re eating—and taking the time to savor our food and enjoy the process of eating is likely to cause us to eat less, again independently of what we’re eating.

Not an environment that encourages savoring food.

It's called 'fast food' for excellent reasons.



It is also most likely the case that eating while distracted—watching TV, working, driving—attenuates the sensory experience of eating, and thereby the satiation response. (Hat tip to alert commenter JKC.) There is much more to investigate here.

Stomach Distention: Necessary But Not Sufficient

Finally we turn to stomach distention: the sensation of being “full”.

I’ve saved the best part for last…so keep reading!

A lot of noise has been made about how “energy density” is the key to dieting—usually by low-fat apostles who never fail to recite the fact that protein and carbohydrate have roughly four calories per gram, whereas fat has about nine. The same theory lies behind the Volumetrics Diet, which pushes high-bulk, low-fat foods as the key to weight loss—and it drives our medical establishment to perform tens of thousands of lap-band surgeries and gastric bypasses every year.

Unfortunately, feeling “full” is not the entire story, as we can demonstrate by one simple fact: if it were, all anyone would need to lose weight is a giant jar of sugar-free Metamucil. Now that we’ve solved the obesity problem, we can all go home, right?

Well, no. As I explained back in Part II, you can fake satiation, but you can’t fake satiety. Eating extremely energy-dense foods can indeed cause us to overeat…but if we’re not getting the energy and nutrients we need, consuming more water and eating more indigestible fiber does not magically make us feel satiated or sated.

In support of this, note the long-term results from stomach stapling (VBG, or “vertical banded gastroplasty”) and lap-band surgery:

J Gastrointest Surg. 2000 Nov-Dec;4(6):598-605.
Ten and more years after vertical banded gastroplasty as primary operation for morbid obesity.
Balsiger BM, Poggio JL, Mai J, Kelly KA, Sarr MG.

“Weight (mean +/- standard error of the mean) preoperatively was 138 +/- 3 kg and decreased to 108 +/- 2 kg 10 or more years postoperatively. Body mass index decreased from 49 +/-1 to 39 +/- 1. Only 14 (20%) of 70 patients lost and maintained the loss of at least half of their excess body weight with the VBG anatomy. Vomiting one or more times per week continues to occur in 21% and heartburn in 16%.

Note that the long-term results of lap-band surgery (“gastric banding”) are very similar: “no significant difference in weight loss was registered between the 2 study groups” (Miller et.al.)

While the average patient maintained a 30 kg weight loss, this didn’t get them even halfway to normal weight: only one in five patients managed to maintain this milestone.

Energy Density: It’s Not The Fat, It’s The Water

Clearly low energy density isn’t a panacea—but it does make some difference to satiation. Let’s take a look at the data!

Besides protein, fat, and carbohydrate, foods typically contain “fiber” (indigestible carbohydrate) and water. While the anti-meat, anti-fat brigade concentrates on 9 vs. 4 calories per gram, we need to take into account the fact that meat is comprised primarily of water.

I’ll handicap the comparison by choosing an extra-fatty USDA Prime grade of prime rib, which contains 367 calories per 100 grams, or about 3.7 calories per gram. (Link.)

In contrast, rice cakes contain 392 calories per 100 grams, or almost 4 calories per gram. (Link.) That’s right: rice cakes are a denser source of calories than prime rib!

That’s because rice cakes, like all shelf-stable foods, have most of the water removed in order to preserve them and retard bacterial growth. As a rule, anything you’ll find in a box on the shelf will be dehydrated—and, in consequence, extremely calorie-dense.

Dehydration and Preservation

We’re all familiar with the phenomenon of stored food getting wet and rotting, or going moldy. Since life requires water, one of the best ways to keep food from spoiling is to remove all the water, and seal it to stop water from getting in—thus preventing bacteria from growing on or in it.

For instance, pemmican is just meat with all the water removed: the fat is separated from the meat and boiled to remove the water, while the meat is air or oven-dried and ground into bits.

Here are some “calories per 100 grams” readings for common “healthy” packaged foods—

—all of which are more calorically dense than prime rib!

In contrast, here are some statistics for whole paleo foods commonly derided as “rich”, “heavy”, and “fattening”:

Furthermore, as long as we’re talking about water, we must take into account the water we consume along with the food we eat. Some studies claim that oatmeal is the most satiating food in the world—but if you don’t allow people to drink, a food made with mostly water will be more ‘filling’ than a drier food, even if the real-world result would be equal bulk due to the drier food making you more thirsty.

A Speculative Hypothesis About Water Intake

Since we require water in order to process salt, it might very well be that a low-salt diet causes decreased water consumption and a parallel decrease in satiation during real-world meal consumption. A similar situation might also occur with bland vs. spicy food: increased water intake with spicy food might result in greater satiation.

If anyone knows any research that addresses this issue, please let me know. Most studies don’t allow or record ad lib water consumption, and therefore aren’t much help.

(It is also the case that it takes more time to chew and eat a less calorically dense food than a more calorically dense food…so density most likely affects eating rate as well as gastric distention. And how much do you have to chew a steak, versus breakfast cereal?)

Finally, we address the standard bulking agent: “fiber”. Most of the controlled studies on fiber address the “heart-healthy” claims and focus on blood lipoprotein levels, but this review conveniently summarizes the available literature relating to weight loss:

Gastroenterology. 2010 January; 138(1): 65–72.e1-2.
Dietary Fiber Supplements: Effects in Obesity and Metabolic Syndrome and Relationship to Gastrointestinal Functions
Athanasios Papathanasopoulos, M.D. and Michael Camilleri, M.D.

Recent meta-analyses of randomized controlled studies (RCTs) suggest only minor effects on weight loss for commonly used DF supplements.

Conveniently, Table 3 lists the studies and their findings—and a quick reading shows that the studies whose only intervention was additional fiber resulted in zero or insignificant weight loss, whereas the studies that resulted in significant weight loss were compound interventions of which fiber was only one small component.

Conclusion: How We Break Satiation

  • Since satiation is an estimate of future satiety based on sensory input, much of satiation is driven by our body’s nutritional needs, and the factors that affect satiety will also affect satiation.
  • Therefore, we can fail to achieve satiation by eating nutritionally incomplete foods, with no protein (or incomplete protein) and few nutrients.
  • Since satiation is dependent on sensory input, we can fool satiation by decreasing sensory exposure to our food—or otherwise attenuating the sensory experience of eating.
  • We can do this by eating quickly, which we usually accomplish by eating food in liquid or other highly processed (and, therefore, pre-digested) forms. It is also likely that caloric density enables quicker eating to some degree.
  • Cultural factors may also play a role in satiation. A culture that treats eating as an inconvenient obstacle to accomplishment, rather than an experience to be savored, seems likely to decrease our sensory exposure to food by eating quickly (“on the run”) or while distracted, thereby reducing satiation and encouraging overconsumption.
  • Decreased caloric density also increases satiation, to a degree—but it is primarily driven by water content, not by calories per gram of macronutrient. Packaged foods are typically far more calorie-dense than whole, fresh foods due to dehydration.
  • Dietary fiber may increase satiation—but since it has no significant effect on long-term weight loss, it clearly has no effect on satiety.

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

Live in freedom, live in beauty.

JS


(Part V of a series. Go back to Part I, Part II, Part III, or Part IV.)

Did you find this article surprising or illuminating? Yes, you did, because you didn’t know that prime rib is less calorically dense than rice cakes.

You can support my continued efforts to inform, educate, and amuse you by buying a copy of my “Funny, provocative, entertaining, fun, insightful” novel The Gnoll Credo. US residents can buy signed copies directly from my publisher, Barnes and Noble offers free shipping to the USA, and it’s available worldwide, with free shipping, through (EDIT: link fixed) The Book Depository.

(Yes, you can still buy it through Amazon.com, but they’re taking at least a week to ship.)

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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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