Satiety

When it comes to dieting, or even trying to gain weight, one of the most influential pieces to success is satiety. Having low satiety during a weight loss phase can lead to some derailment of one’s diet if will power breaks. On the other hand, becoming exceedingly satiated when trying to gain weight is as much an issue as people tend to under eat in those situations. In this article, we will examine the non-pathological physiological phenomena of satiety, as well as improving satiety to be more satiated or less satiated depending on one’s goals.

What is Satiety?
As usual, let us get on the same page. Nutritional satiety is a state in which one is satisfied, full [1][2].


 

How does Satiety occur?
And this is where things get interesting. Satiety is not determined by one simple mechanism, but is a product of many feedback mechanisms. A combination of various mechanisms, as is currently understood, goes as follows:


Eating (A): Otherwise known as mastication, eating can have psychological and physiological benefits in reaching satiety. Eating food increases satiety in the absence of receiving nutrition in another way (Intravenously, for example) – this is a no brainer. If you eat food, you’ll be more satisfied than if you never eat food (shocker!)[3].

Stomach (B): Here, the body uses an extremely influential nerve called the Vagus nerve that sends signals to the brain from the gastric section (stomach, intestines). The signaling sends information about a variety of feedback mechanisms:

1. Gastric Distention: This is the stretch reflex of the stomach. As the stomach expands, signals are sent to the brain that the stomach is being stretched to a certain capacity, increasing the realization of fullness [5].

2. Chemoreceptors: These are sensory pieces that inform the brain about nutrient amount and osmolality (amount of nutrient within a certain amount or measure, for example, 1g of protein per 10g of food stuff)[6].



 

A

B

3. Gastric Emptying: The body does not just release stomach contents into the small intestine willy-nilly, but rather, regulates the release of stomach housed food stuff (chyme). Gastric emptying is regulated in a way that osmolality is in a favorable proportion to the body’s need. Food that has the best proportion (osmolality, in a manner of speaking) is released into the small intestine sooner than less favorable osmolality [6]. The intestine (the point of nutrient absorption) determines the amount of gastric emptying that occurs.

Intestines (C: Fascinatingly, it’s been identified that the body has two physiological types of satiety. One is called gastric satiety and has already been detailed in the stomach section, and the other is intestinal in nature. Intestinal satiety is tricky as a person can be consciously satiated if the intestine has enough volume of food stuff, yet the stomach is not full. These two play-off of one another as intestinal fullness reduces gastric emptying (see previous section) to allow food to accumulate in the stomach once again [6].

1. Hormones: There are several hormones that play a role in satiety by either directly playing a role on satiety (Cholecystokinin, Glucagon-like peptide, etc) or indirectly via impact on various sections of the gastrointestinal region [6][7][8][9][10]. This particular area still needs quite a bit of research; however, as the hormone functionality is still not completely understood.


Liver (D): While we realize that desirability of food, volume of food, type of food, and hormones all play a role in achieving satiety; this is not the end of the story. Other organs, outside of the direct gastrointestinal system play a role in satiety, as well. Blood glucose levels seem to have an impact on satiety in the way they impact other areas, such as gastric emptying during a hypoglycemic tending state [11][12].



 

C

D

                                                                                                            Citations

[1] Satiety | Definition of satiety by Merriam-Webster. (n.d.). Retrieved from http://www.merriam-webster.com/dictionary/satiety

[2] satiety | physiology | Britannica.com. (n.d.). Retrieved from http://www.britannica.com/topic/satiety

[3] Plata-Salamán, C. R. (1991). Regulation of Hunger and Satiety in Man. Digestive Diseases. doi:10.1159/000171310

[4] Snoek, H. M., Huntjens, L., J, G. V., C, G. D., & Weenen, H. (2004). Sensory-specific satiety in obese and normal-weight women. American Journal of Clinical Nutrition.

[5] Schwartz, G. J. (2000). The role of gastrointestinal vagal afferents in the control of food intake: current prospects.Nutrition. doi:10.1016/S0899-9007(00)00464-0

[6] Santoro, S. (2012). Stomachs: does the size matter? Aspects of intestinal satiety, gastric satiety, hunger and gluttony. Clinics,67(4). Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3317257/

[7] Liebling, D. S., Eisner, J. D., Gibbs, J., & Smith, G. P. (1975). Intestinal satiety in rats. Journal of Comparative and Physiological Psychology. doi:10.1037/h0077163

[8] Bi, S., Chen, J., Behles, R. R., Hyun, J., Kopin, A. S., & Moran, T. H. (2007). Differential body weight and feeding responses to high-fat diets in rats and mice lacking cholecystokinin 1 receptors. American Journal of Physiology-regulatory Integrative and Comparative Physiology. doi:10.1152/ajpregu.00002.2007

[9] Little, T. J., Horowitz, M., & Feinle-Bisset, C. (2005). Role of cholecystokinin in appetite control and body weight regulation.Obesity Reviews. doi:10.1111/j.1467-789X.2005.00212.x

[10] LAVIN, J. H., & READ, N. W. (1995). The Effect on Hunger and Satiety of Slowing the Absorption of Glucose: Relationship with Gastric Emptying and Postprandial Blood Glucose and Insulin Responses. Appetite. doi:10.1006/appe.1995.0043

[11] Hlebowicz, J. (2009). Postprandial blood glucose response in relation to gastric emptying and satiety in healthy subjects.Appetite. doi:10.1016/j.appet.2009.06.014

[12] Scharrer, E. (1984). Satiation Mechanism. Z Ernharungswiss,23(4), 241-54. doi:10.1016/j.appet.2009.06.014

[13] Hunger and Satiety. (n.d.). Retrieved from http://users.ipfw.edu/abbott/120/hungersatiety.html

[14] Ahima, R. S., & Antwi, D. A. (2008). Brain Regulation of Appetite and Satiety. Endocrinology and Metabolism Clinics of North America. doi:10.1016/j.ecl.2008.08.005

[15] Farooqi, I. S., Bullmore, E., Keogh, J., Gillard, J., O'Rahilly, S., & Fletcher, P. C. (2007). Leptin Regulates Striatal Regions and Human Eating Behavior. Science. doi:10.1126/science.1144599

[16] Klok, M. D., Jakobsdottir, S., & Drent, M. L. (2007). The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obesity Reviews. doi:10.1111/j.1467-789X.2006.00270.x

[17] ASTRUP, A., TOUBRO, S., RABEN, A., & SKOV, A. R. (1997). The Role of Low-Fat Diets and Fat Substitutes in Body Weight Management. Journal of The American Dietetic Association. doi:10.1016/S0002-8223(97)00737-2

[18] Paddon-Jones, D., Westman, E., Mattes, R. D., Wolfe, R. R., Astrup, A., & Westerterp-Plantenga, M. (0). Protein, weight management, and satiety1-4. Journal of The American Dietetic Association.

[19] ROLLS, B., HETHERINGTON, M., & BURLEY, V. (1988). The specificity of satiety: The influence of foods of different macronutrient content on the development of satiety.Physiology & Behavior. doi:10.1016/0031-9384(88)90230-2

[20] NIWANO, Y., ADACHI, T., KASHIMURA, J., SAKATA, T., SASAKI, H., SEKINE, K., . . . KIMURA, S. (2009). Is Glycemic Index of Food a Feasible Predictor of Appetite, Hunger, and Satiety? Journal of Nutritional Science and Vitaminology. doi:10.3177/jnsv.55.201

[21] Privitera, G. J. (2012). The influence of eating rate on satiety and intake among participants exhibiting high dietary restraint.Food Nutrition Research. doi:10.3177/jnsv.55.201

[22] Why eating slowly may help you feel full faster - Harvard Health Blog - Harvard Health Publications. (n.d.). Retrieved from http://www.health.harvard.edu/blog/why-eating-slowly-may-help-you-feel-full-faster-20101019605

[23] Rolls, B. J., & Roe, L. S. (2002). Effect of the volume of liquid food infused intragastrically on satiety in women. Physiology & Behavior. doi:10.1016/S0031-9384(02)00801-6

[24] Rolls, B. J. (1998). Volume of food consumed affects satiety in men. American Journal of Clinical Nutrition, 67(6), 1170-7. http://www.ncbi.nlm.nih.gov/pubmed/9625090

[25] Rolls, B. J. (2000). Increasing the volume of a food by incorporating air affects satiety in men. American Journal of Clinical Nutrition, 72(2), 361-8. http://www.ncbi.nlm.nih.gov/pubmed/10919928

[26] Snoek, H. M., Huntjens, L., J, G. V., C, G. D., & Weenen, H. (2004). Sensory-specific satiety in obese and normal-weight women. American Journal of Clinical Nutrition, 72(2), 361-8. http://ajcn.nutrition.org/content/80/4/823.full.pdf+html

[27] Institute of Medicine (US) Committee on Military Nutrition Research; Marriott BM, editor. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington (DC): National Academies Press (US); 1995. 11, Effects of Food Quality, Quantity, and Variety on Intake. Available from: http://www.ncbi.nlm.nih.gov/books/NBK232454/

[28] Slavin, J., & Green, H. (2007). Dietary fibre and satiety. Nutrition Bulletin. doi:10.1111/j.1467-3010.2007.00603.x

[29] Samra, R. A. (2010). Fats and Satiety. In Fat Detection: Taste, Texture, and Post Ingestive Effects. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK53550/

Illustrations:

1. https://commons.wikimedia.org/wiki/File:Upper_gastrointestinal_tract.svg
2. https://contemplatingcognition.wordpress.com/2014/01/16/the-brain-within-the-brain/

Brain (E): Certain parts of the brain play more (hypothalamus, cerebral cortex) or less of a role in satiation, but the brain plays a massive role, in general. Specifically, the brain receives and sends signaling to eat or not eat, but is also affected by hormones [13].

1. Hormones: Receptors for a particular hormone, called Leptin, allow the influence of Leptin on the hypothalamus which can either increase or decrease satiety noticeably [14][15]. It is even thought that Leptin can have such a strong impact that it can override a predetermined physiological state of satiety, although this usually only occurs in pathological cases [15]. There are, of course, other hormones (such as ghrelin) that play various roles in this area, but going into each and every hormone would be a book in itself, so just be aware that hormones that act on the brain can have an overwhelming influence – even beyond other physiological conditions [16].

So, satiety occurs if some, or all, of these feedback mechanisms are satisfied. From gastric distention, to the two type satieties (gastric and intestinal), to Leptin’s powerful influence, and everything in-between, these factors all act upon one another to achieve various degrees of satiety.


What are some practices to increase or decrease Satiety?
It is important to understand how satiety is reached so as to determine various methods of using that information to then manipulate one’s satiety during dieting, gaining, or during any number of other circumstances. So, using this information, we have several factors we can change to put ourselves in the best possible position given our circumstance. These factors include, but are not limited to:

Macronutrient Focus
Macronutrients make up the calories, energy that we need to sustain life. Each macronutrient has a specific purpose, but beyond that, in relation to satiety, not every macronutrient is satiable to the same degree.

Protein
Increasing protein intake has been shown, over and over, to increase satiety compared to carbohydrates and fats [17][18]. So, with that information, one could easily increase protein ingestion and feel fuller, longer. Why this is the case is still a matter of conjecture, however. We understand that it does, but we do not know why it does – yet.

Other Macronutrients
While protein is undoubtedly the most satiating macronutrient, by itself or paired with other macronutrients, it might be interesting to quick touch on how the other macronutrients fair in respect to satiety [19]. It seems that the runner up is carbohydrate consumption. While carbohydrates may not be the best macronutrient for achieving maximal satiety, it does still offer more satiety than the alternative – fat [19]. However, there is some proof that the type of fat can decrease the gap in satiety between carbohydrates and fat with medium chain fatty acids and unsaturation increasing satiety [29]. Meanwhile, within the carbohydrate macronutrient are various types of carbohydrates that do have different degrees of influence on satiety, which will be discussed next.

Fiber
Fiber has been shown, at least in the short term, to boost satiety [27][28]. It may do so by having an affect on the gastrointestinal digestion speed by increasing viscosity of food stuff. However, not all fibers are created equal. Only some types of fiber offer the benefits of short term, or slightly lengthened satiety [28].

Glycemic Index
This applies specifically within the carbohydrate macromolecule as this macronutrient comes in various shapes and sizes and has various effects on insulin response and blood glucose changes depending on said make ups. So, does a carbohydrate that has a low glycemic index have an advantage over a high glycemic index carbohydrate in terms of satiety?

Apparently, this is considerably hazier than one might imagine. It seems that glycemic index not only influences satiety directly, but also may influence ghrelin and leptin levels. However, there is not much research on the matter, yet we can address the satiety aspect of glycemic index. It seems that the research indicates that while low GI foods may increase satiety, this satiety is short lived and only advantageous in the short term in comparison to high GI foods [20]. Also, it seems that even more influential than GI is the speed by which certain foods are consumed. Typically, most high GI foods are quick and easy to consume, and the increased rate of consumption may be the reason for accelerated hunger. Taking those same high GI foods and slowing the consumption process staves off hunger, however (more on this later) [20]. This means that the speed of consumption may have a greater effect on blood glucose levels than the actual food itself, and as we know (from the Liver section of this article) that blood glucose and insulin do have an impact on satiety. So, the more stable we can get blood glucose, possibly the greater satiety is achieved, and as most glycemic index foods are rarely consumed in isolation, this is a moot point.

Take away: Consume more protein, and carbohydrate food glycemic index is relatively pointless if consumed in conjunction with other sources of food. Basically, be sure to incoporate protein and fiber in your daily consumption.


Consumption Speed and Quality
This was touched on in the previous section, but for a variety of possible reasons (one discussed last section was blood glucose regulation) for why speed of eating could have an impact on satiety. Well, there is relatively conclusive research that does mention that eating slower does have an impact on satiety [21][22]. In regards to quality of consumption, it is interesting to find that chewing more increases satiety. In measures of the briefly aforementioned hormones cholecystokinin (CKK) and ghrelin were both impacted favorably to increase satiety [23]. This may all be, again, due to more regular blood glucose levels and a more beneficial absorption pattern as well as attenuating the disconnect between gastric satiety reached, but consciousness being unaware (the delayed realization of satiety).

Take away: Chew slower, chew longer, and you will be full longer.


Volume
This seems almost no brainer, but why not attach some science to the conclusion? In terms of volume, the relationship is positive. So, the more volume of food ingested the greater satiety [24][25].

Take away: For more calories, consume calorically dense food, and for fewer calories, consume non-calorically dense foods, but equal volume so as to achieve relative satiety.


Sensory Specific Satiety
Sensory specific satiety is satiety that is dependent on the particular taste, smell, or look of a particular food. So, the idea is if a person were to eat pasta for their meal, their satiety for pasta would increase, but their satiety in terms of other foods may be unchanged or grow; essentially, the hedonic understanding of food. This seems to be the case and as a result, one can be satiated in regards to one food, but crave different foods, especially foods that have a completely different palatability [26]. However, eating a variety of food at once does not lead to an increase in satiety and actually increases the amount consumed [27].

Take away: Eat a variety of foods in terms of sweetness, saltiness, tanginess to decrease satiety; more of one food (salty, for example) to increase satiety of that type of food.


 

E

SUMMARY

It seems clear that there are a number of feedback mechanisms for the body to communicate satiation. Due to this high number of feedback mechanisms, it is difficult to say how influential each is in relation to another; however, it is clear that hormonal influences are among the strongest and in certain cases (leptin) leading to an “override” of previously established physiological satiation. In terms of increasing or decreasing satiation, it mainly depends on type of macronutrient (favoring protein for fullness), volume (more leading to fullness), speed of consumption (slower leading to fullness), and hedonics (variety leading to less satiation and greater consumption). 

Writer: Nicolas Verhoeven

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