Hello Veganthinkers! Thanks for sticking around during my departure from “That Vegan Show” over the last year. If you have been following on social media, you may know that in August 2016, I moved from Missouri to Oregon to pursue a Masters in Nutrition. Moving was a big adjustment, and even though I hoped to continue the radio show on a less consistent basis, this has not been feasible. However, my studies will prepare me for becoming a plant-based nutritionist and possibly even a nutrition/mental health counselor. My passion for the radio show as a medium for activists and nutritionists to disseminate information will lead me to return to hosting a show in the future. My current education will also allow me to be a guest on other radio shows to share what I have learned.
I am taking that opportunity now to share what I am learning about the complexities of hunger, satiety, and thirst. While every factor in our eating and drinking cannot be described in this blog, I will cover a detailed overview of the current understanding of these processes. “Who” are some of the main players in this system – the stomach, the brain? What about external cues and memories of feasting past? You will soon find out how chemicals, organs, and even smells and memories play a role in our eating and drinking habits.1 Speaking of external triggers, it is a little after noon and I have been reading about hunger for a while now. Time for lunch!
Our bodies and brains need sufficient calories, and macro and micronutrients not only to survive, but function optimally. A major player in this hunger game is the hypothalamus.2 The hypothalamus is “a region of the forebrain below the thalamus which coordinates both the autonomic nervous system and the activity of the pituitary, controlling body temperature, thirst, hunger, and other homeostatic systems, and involved in sleep and emotional activity.”3 At the size of approximately a pearl, the hypothalamus has a lot of responsibilities. While this article focuses mainly on hunger and thirst, it will touch upon some of these other systems and how they affect our eating and drinking behaviors. How does the hypothalamus know if we are hungry or full? Let us count (some of) the ways.
After eating a meal with high glucose or high fat, our bodies send hormones into the blood stream which block receptors in the ventromedial hypothalamus; this inhibits hunger.1 The former hormone, insulin, is made in the pancreas and released when there is a high level of glucose, a type of sugar, in the blood.1 However, after it removes the glucose from the bloodstream, we will become hungry again.1 Interestingly, smells and pre-eating behaviors, such as cooking, will also release insulin, removing any lingering glucose in the bloodstream.1 This is one of the reasons smelling food makes us hungry. The latter hormone, leptin, is created in our adipose tissues, more commonly known as fat stores.2 So the more of these stores a person has, the more leptin is in the bloodstream, slowing down hunger signals.1,2 After its discovery in 1994, there was hope that leptin would have an important impact on skyrocketing obesity rates.4 Unfortunately, over a decade of research indicates that taking supplemental leptin only helps a small percentage of overweight people.4 Our bodies seem to become resistant to both leptin and insulin when they are overproduced.1,4 Several theories exist about why this happens, but there does not seem to be a definitive explanation.
But what role does the stomach play in hunger? Ghrelin is produced mainly in the gut under a variety of circumstances.1,4 If the stomach is devoid of food and “growling,” ghrelin is manufactured.2 However, regularly scheduled meal times and seeing and smelling food can trigger it too.4 This hormone stimulates hungers by targeting the lateral hypothalamus and other parts of the brain.5 As you have already gathered, our bodies have complex systems of regulation.1 The human body keeps its systems within a narrow range; this form of checks and balances is referred to as homeostatis.1 So typical regulation patterns are not the only influence on this feedback loop. Studies have suggested that stress and sleep can also affect ghrelin levels, causing them to be too high, leading to overeating and weight gain.5,6
If only the gut and the hypothalamus were the only mediators in our hunger control. There are more central and peripheral factors that influence our hunger and satiety system.1 Central factors are based on input from the central nervous system. Other parts of the body that affect hunger and satiety are referred to as peripheral factors.1 In the previous example, ghrelin is the peripheral factor that influences the lateral hypothalamus (central factor).1 These two factors intertwine to regulate our appetites.1 Many of you may have heard about the glycemic index.1 For the sake of simplicity, high glycemic foods have high sugar or refined carbs and are lacking in fiber.1 Foods high on the glycemic list keep people hungry, while foods low on the list increase satiation and lead to a longer period of not eating afterwards.1 Likewise, high fat foods and large quantities of food have been found to lead to satiation.1, 2 Under these conditions, the upper intestine releases cholecystokinin (CCK), a short-acting peptide that travels to the brain sending a strong signal of satiation. To offer more long-lasting feeding secession, the hormones GLP-1 and YYP are released from the lower small intestine.1,4 Not only do they send a signal to your brain that you are satisfied, but they also stop your stomach from processing any more food.4 Therefore you feel full longer, stymying further eating.4 In addition, GLP-1 stimulates the pancreas to release insulin, which picks up and delivers glucose to the cells or stores them as adipose tissue.4
Besides these physiological players, as hinted at previously, there are external and environmental factors that play a role in our eating patterns.1 As mentioned earlier, odor, behaviors that usually precede eating, smells, and sounds can all trigger eating.1 Additionally, cultural experiences, learning, and memory play a role in our eating habits.1 Remembering a festive occasion with family with an abundance of food drives our bodies to repeat the experience. On the other hand, being mindful while eating a meal can lead to eating less later and better memory of what was eaten.1 I am sure scientists will be discovering new physiological and environmental factors that influence hunger and satiety for as long as humans exist.
Let’s move on to another important homeostatic system of the body, thirst. Thankfully, eating provides some of the liquid content we need to survive.1 For example, lettuce is 96% water.1 Interestingly, people not only drink water when their bodies are at a suboptimal level (homeostatic drinking), they also drink preemptively (nonhomeostatic drinking).1 It is important to emphasize the drinking of water, versus other beverages. Liquids containing alcohol or caffeine trigger urination, which depletes water stores.1 When drinking on a homeostatic basis, the amount of food eaten plays a role in the amount of water that is drank.1 When a person has been without food, they drink less water while eating. Conversely, well satiated people drink more liquids.1 This helps to maintain the balance of water and food in the gastrointestinal tract.1 The body also likes to keep its salt/water ratio in balance as well as other substances. Drinking will increase when these substances exceed the correct concentration.1 When too much salt is in the bloodstream, water will flow out of the cells. This disproportion triggers thirst to restore the balance, lest our cells become dehydrated.1 Loss of blood can cause a loss of fluid outside of the cells. If hospitals did not administer restorative intravenous fluids, thirst would occur to rectify the fluid loss.1
Water is so vital to our survival (60-70% of an adult body mass), we do not wait until we need water or at a deficit to consume it in conditions where it is readily available.1 Humans and other animals drink in an anticipatory fashion. Even though water in not needed until several hours after eating, animals will drink while eating. They may drink more while consuming salty foods.1
Now let’s discuss a couple of theories about thirst. Early researchers thought that a dry mouth was the cause of thirst; however, now it is postulated that it is a signal of thirst.1 The lateral hypothalamus is involved in receiving and responding to signals in order to regulate water.1 Furthermore, the hypothalamus releases antidiuretic hormone (ADH) which acts on the kidneys to retain water rather than passing it as urine.1 ADH is released in various conditions including lack of intracellular or extracellular fluid and a drop in blood pressure.1 Other regulators are the hormone angiotensin and the enzyme renin.1, 7 Blood is frequently cycled through the kidneys and increases in sodium or a decline in arterial pressure are recognized.1, 7 As renin from the kidneys enters the bloodstream, angiotensin forms.1 Angiotensin triggers the brain to compensate for the deficiency of fluid in the blood supply and the body.1 It also stimulates the release of additional ADH.1 Our amazing bodies have so many controls to keep our bodies in order. Through meditation practice, I am reminded to thank my body for all the hard work it does to take such good care of me.
I hope this information about hunger, satiation, and thirst clarified some of the complex ways our body keeps us functioning. Come back in a few weeks and I will add any comments or corrections provided by my professor on this piece.
Please follow along for future releases of archived and new radio shows. Next up to be edited is an archived interview with Jessica, board member of Out to Pasture Sanctuary to Pasture Sanctuary in Estacada, Oregon. Speaking of OTP, they are having a fun event this Saturday, October 28 – Trick or Treat for the Animals or Treat for the Animals. Hope to see some of you there!
1. Logue AW. The of Psychology Eating and Drinking. Routledge; 2015.
2. Hormone control of hunger. Khan Academy. https://www.khanacademy.org/test-prep/mcat/biomolecules/hormonal-regulation/v/hormone-control-of-hunger. Accessed October 21, 2017.
3. hypothalamus | Definition of hypothalamus in English by Oxford Dictionaries. Oxford Dictionaries | English. https://en.oxforddictionaries.com/definition/hypothalamus. Accessed October 21, 2017.
4. Kluger J. The Science of Appetite. Time. http://content.time.com/time/specials/2007/article/0,28804,1626795_1627112_1626670,00.html. Published May 31, 2007. Accessed October 21, 2017.
5. Mandal MDDA. What is Ghrelin? News-Medical.net. https://www.news-medical.net/health/What-is-Ghrelin.aspx. Published September 17, 2014. Accessed October 22, 2017.
6. Broussard JL, Kilkus JM, Delebecque F, et al. Elevated ghrelin predicts food intake during experimental sleep restriction. Obesity. 2015;24(1):132-138. doi:10.1002/oby.21321.
7. Nelms M, Sucher K. Nutrition Therapy and Pathophysiology. Cengage Learning; 2015.