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.
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. BenelamWhen 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. KringelbachLiking: 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.
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 BerridgeFood 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.)
Are you finding this series valuable? Does this breakdown allow you to explain hitherto confusing concepts? Leave a comment, and spread it using the buttons below!
I like it JS. This might help explain patients why after eating SAD they may feel temporarily full (=satiation) but not entirely satisfied (=satiety). It doesn’t matter how stuffed you feel after eating 2 packets of crisps, you will “want” more food. I like the simplicity of this language because as you rightly pointed out the discussion on hypothetical biochemical pathways can now be relegated to “fascinating but not practical”.
Looking forward to Part 3.
“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.”
Very interesting. The memories and good experiences I’ve had eating certain foods definitely reinforce my wanting to eat them again. Sushi for instance, I was praised to being able to handle the heat of wasabi.
“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.”
Hamburgers don’t really look fattening do they? French fries even look like health food.
Can’t wait to read your book
I’ve enjoyed both parts 1 and 2 of the “Why we are hungry”. It is cool to look at the science of why we get hungry. Will you be addressing the other component of eating, “The psychology of Why We Eat”? We eat because we are bored, angry, and a host of other emotions, both positive and negative. We eat for entertainment. We eat to replace other actions that we can’t fulfill. I’ll be looking forward to that series. Grok on!
Anastasia:
Absolutely! Understanding the difference between satiation and satiety helps us understand a lot of problems, including why snacks don’t substitute for meals. And that’s just the beginning.
Calvin:
Yes, experiences absolutely do affect our likes — and even our perception of satiation. It’s fascinating, and it’s one of the reasons this has turned into a multi-part epic.
Thank you for buying a copy of The Gnoll Credo! It will change your world, and you’ve helped keep gnolls.org updated and ad-free.
Bodhi:
I’ll definitely be touching on the issues you mention. Good to see you again!
JS
An interesting second chapter – I didn’t think the first part could be developed that much further but the first most important notion to me from that first part is that fine tuning can and should be made even within a largely no-brainer dietary regimen like paleo.
Understanding likes and wants, and understanding that satiation can be tricked is vitally important in achieving proper satiety. I often make up small taster dishes and we like to eat a few smaller courses rather than one large course. That variety can quickly add up to satiation; the trick, if that is the right word, is putting together meals of any style, any number of courses that do not require the body to be fed again after an hour or so.
This second part has that detail.
After reading the article, I find myself thinking very much along the same lines as Bodhi – the psychology of food is very powerful, for both sexes, for the same and very different reasons.
I do like your phrase, “Any animal whose faulty perceptions and motivations caused it to become obese, emaciated, malnourished, or poisoned by excess would have been strongly selected against” … Mark Sisson briefly raises the notion of passing on broken genes through reproduction in his ‘The Primal Blueprint’. I’ve touched on it before about how reproduction is now seen as a right in the western world, whether or not the offspring can be afforded, provided for, cared for or raised well. Breeding a downward spiral in our species or future genus seems inevitable. Time for a new homo species?
… while we’re on “broken animals”, it seems we (well, “you”) are so at odds with ourselves that we’re now officially quite broken in our minds as well as bodies: http://science.slashdot.org/story/11/07/16/036230/Mass-Psychosis-In-the-USA … I can laugh, but shudder because “we’re” next – the UK seems to follow the US and ride that crest for Europe.
Thankfully some of our species are quite well. Are we the new supermen?
Did you catch that article on MDA around how barefooters gain all manner of electrical charge from the earth? We already know our prioperception is significantly enhanced, but are we gaining superhuman powers from our lifestyle? Time for a new species!
I have experienced what you are saying first hand… I cannot remember ever feeling ful from a meal and could eat more as I was cleaning up the dishes. I was constantly hungry. I started eating Paleo/Low carb a few weeks ago. What a relief to NOT FEEL LIKE I AM ON EDGE all the time. I feel relaxed, & rarely think about food. Relief is a small word for what I now feel like.
This week is our 4H county fair. I had to be out there every day to man a booth for a couple of hours.. Elephant ears abound. Every fried,sweet,cold and creamy confection you can think of is there.Cinnamon wafts through the air.
But… There are also 4H booths that sell 4H raised pork chops, rib eye steaks, Roasted rabbit legs.
It is 100 degrees here and a cold giant ice cream cone sounds fabulous, but the feeling of hunger that will haunt me for days after eating it is not worth one bite of it.
There is a church booth that is giving away free ice water and I know how 4H animals are raised. I am having a great week. No need to grocery shop this week. I have had rabbit,sirloin tips, pork shops…In the morning I hit a church booth and have two eggs over easy and a small steak.
I have only had to eat twice a day, cause I am not hungry. I do not think about food.- I feel incredible.
Paul:
This is just the beginning. Now that I've laid the theoretical groundwork we can start tackling problems.
And we are absolutely deteriorating as a species. Most mutations are deleterious…so the general trend is towards impaired function, impaired health, and susceptibility to disease. Natural selection is the reason life didn't deteriorate into dysfunctionality hundreds of millions of years ago: non-impaired individuals reproduced at a higher rate than impaired individuals, so impairments were selected against.
No longer. No impairment is selected against in the Western world, and the only thing we are selecting for is fecundity.
However, speciation takes a long time…humans and Neandertals were still able to interbreed after hundreds of thousands of years. I don't see a Morlock/Eloi situation.
lynn:
Yes. “Feeling full” is a component of satiation. Getting satiation back in line with satiety is a necessary step for sustainable healthy eating. I'll be talking about this more next week.
JS
Great article. I was having a discussion a few days ago about meal frequency with some friends and how one of them felt like eatig 6 times a day or so while me and the other one mostly eat twice.
They both argued lots of smaller meals are supposedly better. I haven’t looked much into it, but I wonder how much of that has to do with what people usually eat and this disbalance between the factors you mentioned.
Anyway, very goo article, looking forward to the next ones.
Fmgd:
The advice to “eat every few hours” has a lot to do with eating foods that don't produce satiety. If you satiate yourself, you'll stop eating…but if you haven't been sated, you'll be hungry again once your body digests enough of your food to realize that and send that signal. Can you see why I draw the distinction between the two?
Again, we'll be into the consequences next week.
JS
the argument on 6 smaller meals vs 3 larger is laid out on leangains.com but basically it is because when you eat metabolism is spiked (TEF)
problem being is that the amount your metabolism is boosted is directly related to the amount of calories you consume (different macros also have effect, but i’m not sure we know exactly how beyond protein does it more)
so if you eat 2500 over 6 meals or 3 meals the boost in metabolism will be the same over the course of a day.
plus advice to take in aminos every 3 hours for lean muscle gains is something spead about by supplement companies as it helps sell their products.
looking forward to next installment!
http://www.leangains.com/2010/10/top-ten-fasting-myths-debunked.html this is the article
on that note i think a lot of satiety issues occur with processed foods simply because more of the weight is actually calorific.
steak is roughly 10% weight as fat and 20% protein, 70% water and other non-caloric “stuff”
cheese is 25% protein 35% fat so 40% water.(or other non-caloric stuff)
whereas crisps are 100% caloric load (plus salt and stuff) which is probably where these food producs bypass body signals.
plus the whole empty calorie thing all starch which we have no requirement for whereas fat and protein we have requirements for
Eddie, Stanton,
Thanks. Also, I’ve noticed some research correlating (yeah, I know) more regular meals with lower BMI. Besides the usual confounding factors, I wonder if having food lower in nutrients in a more spread pattern doesn’t mean when you do get to eat you might over compensate, or if the mechanism for that wouldn’t be affected that way.
After spending a few months there, I actually got to start liking natto. Never did crave it though, as I did many other things I can’t technically say I “like.” Chicken heads and oysters are among them. I don’t enjoy eating them, but I sure as hell want them…
eddie:
There are many components to satiety and many problems with processed foods, of which density is just one of them. I'll be talking about those soon!
Fmgd:
What is meant by “more regular meals”? More meals, or meals eaten at more regular times?
Jade:
Something I'll be talking about as this progresses is the fact that experience can modify our likes and wants, and we can consciously choose to disregard (to some extent) our likes and wants, which we call “restraint”. But counting on restraint is generally a bad idea in the long run, as we see by the fact that most diets don't stick: people lose weight and then gain it all back.
JS
Mind over milkshakes: mindsets, not just nutrients, determine ghrelin response. Crum, A. J. et al., Health Psychology 2011 Jul;30(4):424-429.
Could you possibly cover how the concepts of being sated/satiated would apply to intermittent fasting (16/8, 20/4, etc versions)?
My n=1 evidence shows that I become satiated after eating my “first” meal (lets say, 12oz ribeye) but I can still eat more, and do, shortly after (30 min to 3 hrs later). Basically, I eat a lot in a short time span.
Also – would this mean that the body would actively seek to maintain its current body mass (aka: set point theory)? Put another way, I haven’t received enough nutrients/calories/etc to maintain 500lbs, thus I require more, signal hunger cue?
fmgd: check the link i posted above and he goes into that in good detail.
initially most of the epidemiological studies will have picked up on a certain type of person who eats more regularly: those with weight loss goals who also exercise don’t eat crap and count calories, compared to the people who eat 3 squares and of course they will weigh less.
the other thing is that meal skippers (breakfast typically) are often the people who will then grab a donut or other high sugar junk food item, compare them to 3 squares and they’ll probably score higher BMI’s, but compare them to deliberate IFers and you’re likely to get a totally different result.
Stanton,
I meant to type “more, regular meals”, as in more meals in regular intervals.
Eddie,
Thanks. I had read it already, and those are the “usual confounding factors” I meant.
@Both of you,
I haven’t made yself clear, sorry. My question is basically if having low satiety for a long time would mean a spike in want which would in turn (and this is the link I’m not completely sure of) make satiation harder to attain, maybe even (at least) in part due to a higher reward in the diminishing returns scenario.
I just realised I’m kinda asking if prolonged hunger can make one overeat lol
Throwing something into this potential reply, it is often said that if you eat slowly you feel full on less food. Gorging when you're hungry, as in packing down as much food as you can in as short a time as you can will lead to feeling full without necessarily getting to the point that your body has all it will need for a few hours. Eat more slowly and you might reach that point long before you've finished the mass of food in front of you. So long as it's “real food”.
Since going paleo, I use the following as my indicator – if I've eaten a meal and I long for a dessert, I have not made a “good meal”. I learn from that and adjust the proportions accordingly for the next meal, savouring hunger in between. Read J's post on ghrelin! If I make a meal and I am not fulfilled, bodily, I have failed. That said, our primitive man might well have been in that situation often and relied more upon simply stuffing himself as full of fresh meat as he could, gnawing on some plants later on when the desire to eat more (variety) hit him.
I'm not answering anything here, just dropping something more into the dish
Fmgd:
As a counterpoint to the “eat frequent meals” dogma, there is this study.
And as far as “I just realised I'm kinda asking if prolonged hunger can make one overeat lol”, the answer is “Well, yes, but it's important to look at the parts of the argument and make sure they add back up to a sane real-world result”. If they didn't, then my motivational disassembly would be worthless. A lot of science is figuring out how something works that everyone already knows to be true.
Melissa:
The problem is that while ghrelin varied sharply, actual ratings of hunger didn't. “For the measure of hunger, these analyses produces no significant main or interaction effects as a function of shake, time or restrained eating.”
So it's an interesting data point, and I'm a big ghrelin fan…but ghrelin isn't just the “make you hungry hormone”. As I said, we still don't fully understand the biochemical cascades and equilibria.
Evan:
I get the same reaction. If I IF and don't absolutely pig out at my first meal, I can still eat more a couple hours later, as soon as some room gets cleared out in my stomach.
There's a great study in my “The Breakfast Myth” series which shows breakfast skipping is not completely compensated for by lunch and dinner calories. So you're definitely eating a lot…but, most likely, not quite as much as you would have otherwise.
Paul:
I tend to use how I feel a couple hours later as a guide. As I mention above, satiation can be fooled, and dessert (for me) isn't a reliable guide: I can always pack in some ice cream or cheesecake.
That being said, I've definitely had the “my stomach is bloated with food but I'm still hungry” feeling, due to not eating what my body needed at the time.
JS
Sure, I agree on the importance of looking at the separate components, if it sounded like I didn’t I worded it poorly. My main doubt is wether low satiety could make satiation harder to attain or, since satiation might be somewhat more “mechanical”, if it simply raised want so that you’d have to eat more before you feel like it’s not worth it anymore.
Oh, and thank for the link.
Fmgd:
Lack of satiety affects all the other components. I'll be discussing that very soon!
JS
“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.”
So this explains why my asian friends are all so damn skinny. There is only so much food you can fit on a chopstick compared to a fork. Therefore people from asian cultures can only eat in small bites. Mystery solved!
MarkD:
There are a lot of factors, but that's probably one of them. Rice as a source of starch vs. wheat is another.
JS
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Hi,Stanton. Thank you for this great series of articles. I’ve learned a lot form it. Can I translate these articles to Chinese and post it on my blog?
wangfeng:
Contact me through http://www.gnolls.org/contact/ and we'll discuss it!
JS