(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
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
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.
(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.
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