Appetite control, or suppression as some refer to it, is a complex symbiosis of hormonal, environmental, behavioural and bacterial influences.
Yep, I said bacterial. We’ll get to that in this article, don’t worry.
Throughout my study years, working in health food shops, “appetite suppression” was definitely in the top two requests for help.
What I said then is what I’ll say now. Just to better align expectations about what this article will offer.
Suppressing your appetite can be like going to the beach, kneeling at the ocean’s edge and trying to stop the waves from coming in.
It’s challenging to say the least, but understanding it better is an excellent place to start.
Today we will look deeper into what we know about the dynamics of hunger, the desire to eat and appetite control. I’ll also offer some ideas on how you might be able to influence them over time, especially via the gut and brain connection that we’re all about on this website.
Let’s explore how hormones in the digestive system are central players in your hunger and fullness experiences.
New to what hormones are?
Hormones affect nearly every organ of the body.[1] The best way to think of them is as molecules that initiate some form of action at a specific site. Another definition I like is that they are messengers carrying signals through the blood to target organs.[2] The message receiver, often a receptor within a cell, is responsible for acting on the signal.
Now before you ask, let’s differentiate between hormones like oestrogen and progesterone and the hormones we see in digestion.
What the body makes hormones from differentiates how hormones are classified.
For example, oestrogen, progesterone and testosterone are made out of cholesterol and, because of this, are called steroid hormones. All other hormones are made from parts of protein called amino acids.
If you are new to amino acids, they are the components that all link together to make up the protein in your food. Amino acids have many bodily functions, but the important one here is that all other hormones aside from the steroid hormones are made of amino acids. Most notably, the hormones in the digestion that influence your hunger.
A little-known fact is that the digestive system is the body’s largest hormone-producing organ.[3]
If you are new to the gut and the brain connection, you can read more about it here. All you need to know, for now, is that gut hormones work closely with the brain through a portion of the nervous system connected to the digestive system called the enteric nervous system.
Yep, the digestive system has its own nervous system.
These hormones play varying roles that allow the brain to interact with the digestive system around the quality and quantity of food. They also play a role in digesting your food and distributing the energy it draws from the food, and our theme for this article, managing your appetite control.
Let’s look at some of the main hormones involved in appetite control.
To make it easier, but to also give a sense of how hormones contribute to the digestive process, let’s begin with gastrin, one of the crucial hormones to understand in the stomach.
Gastrin’s primary function is to manage the hydrochloric acid levels in the stomach.[4] One of the other functions is to protect the lining of the stomach, small intestine and colon.[5]
Ghrelin, also produced in the stomach, is essential to appetite control.
Its central role is to stimulate your hunger. A study conducted in 2004 confirmed this when higher levels of ghrelin were measured in people just before they initiated eating.[6]
Ghrelin is another excellent example of the influence the brain has on digestion. Ghrelin’s effect on the way the body uses energy from food is driven mainly by the part of the brain called the hypothalamus.[7] One of the key functions of ghrelin is for the brain to know the body is fed and to influence something called gastric emptying, which affects how full you feel.
Remembering that ghrelin’s primary function is to make you hungry, it’s interesting to hear about the various factors that influence it. Of course, food intake is the first and principal factor that reduces ghrelin.[8]Circulating ghrelin also decreases with age,[9] glucose[10] and insulin[11] but is higher in females than males.[12]
Some research has shown how to lower ghrelin levels.
Most notably, a high-fibre meal has seen circulating ghrelin levels decrease.[13] Another study also suggests that your fibre intake can predict your ghrelin levels, which can influence how much ghrelin decreases after you eat.[14]
An interesting side note is that combining foods with bioactives called polyphenols and high-fibre foods can help decrease your hunger. This combination can improve the way your body deals with triglycerides and other fats that can build up. Combining these two also contributes to improving cardiovascular and stroke risk down the line.[15] The source of fibre in this study was carob for those interested.
But I’m getting distracted as usual; other dietary interventions assist with reducing circulating ghrelin levels and regulating your hunger cues.
The main one was meals higher in carbohydrates. At least when compared to meals/diets with higher levels of fat in a small study from 2003.
When measuring circulating ghrelin in healthy women, levels decreased after both the carbohydrate and fat meals. The maximum amount decreased was significantly higher in the carbohydrate meal. This larger, more significant decrease caused a greater level of hunger suppression, which the researchers could match up with ghrelin levels in the blood.[16]
Based on what we know above and other markers measured in the blood during this study, the reason why the ghrelin and hunger suppression occurred at greater levels was down to the higher carbohydrate meal increasing insulin and glucose levels. Something we know reduces ghrelin.
I’ve highlighted this because a common misconception is that carbohydrates can make you hungry and are in some way wrong for you.
Don’t get me wrong. Not all carbohydrates are created equal. But consider that the “good” carbohydrates often come with higher levels of fibre, and you have three contributing factors bringing down your hunger after a meal!
Sounds like a natural manoeuvre for appetite control?
And this is just from the stomach.
A small note about the relationship between protein and ghrelin.
Honestly, the research is conflicting regarding whether or not it helps with hunger suppression. However, one thing I will say about protein and its contribution to hormones like ghrelin is that they are all built out of protein! Yep, we touched on it earlier in the article, but it’s worth bringing up again.
Let’s move to another hormone made in the small intestine, cholecystokinin or CCK, as we’ll refer to it from now on.
CCK is one of the key hormones for the digestion of protein and fat.
One of CCK’s first discovered functions was to signal the gall bladder and pancreas into action to digest fats and protein.
If ghrelin is the hormone that initiates the hunger that makes you eat, then CCK is the quarterback that directs the digestion once you’ve eaten. It signals a decrease in gastric juice (think hydrochloric acid). It regulates the movement of the digestive tract, a process called motility, which allows a slow, consistent flow of food into the small intestine for digestion and entry into the body.[17] CCK also does something vital for satiety. It stimulates another hormone called leptin that acts on the brain resulting in the sensation of feeling full.[18]
CCK also has an intense effect on the fear and anxiety centres in the brain.
Let’s get distracted a little bit and emphasise another example of the relationship between the gut and the brain.
Before we jump back to the role of CCK and how it helps you stay full, an interesting part of the research into CCK’s role in the body is its contribution to anxiety.
We see high levels of CCK in the emotional part of the brain called the limbic system.[19] Whilst studies are in their early stages; initial reports suggest that CCK can make people with anxiety and panic symptoms more sensitive.[20]
Let’s go back to the subject, appetite.
People who have diet-induced obesity are less sensitive to the effects of CCK.
But a few different dietary interventions can manage this for you.
I wonder if you can guess the first one?
A high-fibre diet can enhance the CCK system via soluble fibre’s ability to increase molecules called short-chain fatty acids made by the bacteria in your gut. [21]
I did mention we’d talk about bacteria at the beginning of the article!
Yep, you guessed it. A high-fibre diet makes the body more sensitive to the effects of CCK. This improved sensitivity, in turn, helps you both digest your food better and tell your brain that you’ve eaten enough.
Interestingly, a western style diet that can increase inflammation in the body can inhibit the effects of CCK. Early studies in animals show that high fat and high carbohydrate diets cause an increase in CCK resistance.
Something that makes me wonder if that’s why people who struggle with their mental health commonly gravitate towards processed foods commonly found in the western diet. If increased CCK can make you anxious, then less of it might be unintentionally therapeutic?
Not science, just me on that one; I could be way off!
I wasn’t lying when I said that appetite control is a complex business.
What do you think?
Appetite control mediated by the gut and the brain is one of those subjects where you can get lost in the galaxy of connections between different hormones, receptors and everything in between.
My hope is that you have gained an idea about how the brain and the gut combine to regulate both the function of your digestion and, from there, your hunger and fullness cues.
I also hope that this proves to be yet another example of how a high-fibre diet can be beneficial to managing the gut and brain connection and, in this case, your appetite control!
Hope this helps xx
[1] Campbell M, Jialal I. Physiology, Endocrine Hormones. [Updated 2021 Oct 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538498/
[2] Stárka L, Dušková M. What is a hormone?. Physiol Res. 2020;69(Suppl 2):S183-S185. doi:10.33549/physiolres.934509
[3] Ahlman H, Nilsson. The gut as the largest endocrine organ in the body. Ann Oncol. 2001;12 Suppl 2:S63-S68. doi:10.1093/annonc/12.suppl_2.s63
[4] Prosapio JG, Sankar P, Jialal I. Physiology, Gastrin. [Updated 2022 Mar 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534822/
[5] Parikh A, Thevenin C. Physiology, Gastrointestinal Hormonal Control. [Updated 2022 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537284/
[6] Cummings DE, Frayo RS, Marmonier C, Aubert R, Chapelot D. Plasma ghrelin levels and hunger scores in humans initiating meals voluntarily without time- and food-related cues. Am J Physiol Endocrinol Metab. 2004;287(2):E297-E304. doi:10.1152/ajpendo.00582.2003
[7] Klok MD, Jakobsdottir S, Drent ML. The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obes Rev. 2007;8(1):21-34. doi:10.1111/j.1467-789X.2006.00270.x
[8] Nakazato M, Murakami N, Date Y, et al. A role for ghrelin in the central regulation of feeding. Nature. 2001;409(6817):194-198. doi:10.1038/35051587
[9] Rigamonti AE, Pincelli AI, Corrà B, et al. Plasma ghrelin concentrations in elderly subjects: comparison with anorexic and obese patients. J Endocrinol. 2002;175(1):R1-R5. doi:10.1677/joe.0.175r001
[10] Nakagawa E, Nagaya N, Okumura H, et al. Hyperglycaemia suppresses the secretion of ghrelin, a novel growth-hormone-releasing peptide: responses to the intravenous and oral administration of glucose. Clin Sci (Lond). 2002;103(3):325-328. doi:10.1042/cs1030325
[11] Anderwald C, Brabant G, Bernroider E, et al. Insulin-dependent modulation of plasma ghrelin and leptin concentrations is less pronounced in type 2 diabetic patients. Diabetes. 2003;52(7):1792-1798. doi:10.2337/diabetes.52.7.1792
[12] Barkan AL, Dimaraki EV, Jessup SK, Symons KV, Ermolenko M, Jaffe CA. Ghrelin secretion in humans is sexually dimorphic, suppressed by somatostatin, and not affected by the ambient growth hormone levels. J Clin Endocrinol Metab. 2003;88(5):2180-2184. doi:10.1210/jc.2002-021169
[13] Nedvídková J, Krykorková I, Barták V, et al. Loss of meal-induced decrease in plasma ghrelin levels in patients with anorexia nervosa. J Clin Endocrinol Metab. 2003;88(4):1678-1682. doi:10.1210/jc.2002-021669
[14] St-Pierre DH, Rabasa-Lhoret R, Lavoie ME, et al. Fiber intake predicts ghrelin levels in overweight and obese postmenopausal women. Eur J Endocrinol. 2009;161(1):65-72. doi:10.1530/EJE-09-0018
[15] Gruendel S, Garcia AL, Otto B, et al. Carob pulp preparation rich in insoluble dietary fiber and polyphenols enhances lipid oxidation and lowers postprandial acylated ghrelin in humans. J Nutr. 2006;136(6):1533-1538. doi:10.1093/jn/136.6.1533
[16] Monteleone P, Bencivenga R, Longobardi N, Serritella C, Maj M. Differential responses of circulating ghrelin to high-fat or high-carbohydrate meal in healthy women. J Clin Endocrinol Metab. 2003;88(11):5510-5514. doi:10.1210/jc.2003-030797
[17] Okonkwo O, Zezoff D, Adeyinka A. Biochemistry, Cholecystokinin. [Updated 2022 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534204/
[18] Konturek JW, Konturek SJ, Kwiecień N, et al. Leptin in the control of gastric secretion and gut hormones in humans infected with Helicobacter pylori. Scand J Gastroenterol. 2001;36(11):1148-1154. doi:10.1080/00365520152584761
[19] Francesco Crespi (2019) On the Role of Cholecystokinin (CCK) in Fear and Anxiety: A Review and Research Proposal. Journal of Human Psychology – 1(2):1-10.
[20] Bradwejn J, Koszycki D, Shriqui C. Enhanced sensitivity to cholecystokinin tetrapeptide in panic disorder. Clinical and behavioral findings. Arch Gen Psychiatry. 1991;48(7):603-610. doi:10.1001/archpsyc.1991.01810310021005
[21] Cawthon CR, de La Serre CB. The critical role of CCK in the regulation of food intake and diet-induced obesity. Peptides. 2021;138:170492. doi:10.1016/j.peptides.2020.170492
