Updated: Jun 21
Hormones of Hunger and Satiety and Timing of Digestion
In this science post we are continuing the conversation discussing the hormones that are involved in digestion and are important to weight loss.
We will be focusing on the hormones that are imperative to regulating our hunger and feelings of satiety, or what we at Weight Loss By Gina like to call, eating to satisfaction! We will also be looking at the concept of breakfast and how making it high in protein sets up our day for success. Finally, we will conclude our discussion on digestion by looking at how long it takes our bodies to process and digest the foods that we eat. All of these topics can give us more insight into the “rhyme and reason” behind the different tweaks and the organization of The Livy Method Food Plan, and how it promotes weight loss.
In the science post The Migrating Motor Complex (MMC) and Hunger, we discussed how the feeling of “hunger” is a fairly complex concept that can be influenced by many things including physical/physiological, emotional, social, economic, and mental factors. In fact, many of us have lost touch with gauging hunger signals, or never really become in tune with them in the first place.
We discussed strategies for reconnecting with these signals such as journaling, using a hunger scale, revisiting the four mindfulness questions at every meal and snack. We also discussed the importance of being in the moment when you are eating, minimizing distractions, to really tune into your food and how it is making you feel!
Let’s dive in a bit deeper and look closer at the physiological processes that occur in our bodies that drive our feelings of hunger, but also lead to our feelings of satisfaction when we have eaten enough.
What are hormones?
Hormones are defined as a special substance produced in the body that contains “chemical messengers” that control and regulate the activity of certain cells or organs (Davis, C.P., 2021, March). They are secreted into the blood or extracellular fluid by one cell and in turn, alter the functioning of other “targeted” cells. These target cells may be in glands, tissues, and other cells. The target cells recognize the hormone circulating that is specific to it, and become a “receptor” allowing the hormone to activate it! In fact, many hormones are active in more than one physical process and may have multiple functions!
Many hormones are secreted by special glands and are essential for every activity of life, including the processes of digestion, metabolism, growth, reproduction, and our mood.
There are two types of glands. Endocrine glands, which are ductless glands that release the hormones they make directly into the bloodstream. These glands form part of what we know as the endocrine system. The other type of gland that is present in the body is called an exocrine gland (for example sweat glands and lymph nodes). These are not considered part of the endocrine system as they do not produce hormones, and they release their product through a duct.
Neurotransmitters, although not specifically hormones, are also special chemical messengers that help carry, promote, and balance signals between neurons (also known as nerve cells) and target cells throughout the body. Neurotransmitters are more specific to the central nervous system.
Neurotransmitters can also have strong influences on our hunger and satiety cues and signals!
Here is a great video that briefly talks about hormones and how they work in the body.
This video explains the endocrine system for those that want to learn a little more about how it works!
This video talks about how neurotransmitters travel across neurons in the body.
Now that we understand a little more about how hormones and neurotransmitters work in our body, let’s talk about how these chemical messengers influence our hunger, satiety, and can influence weight loss!
As we discussed in the science post Hormones Important to Weight Loss & Digestion Part 1-Insulin, the pancreas has a major role in digestion by producing and secreting digestive enzymes. However, it also produces the hormone insulin, which is responsible for regulating and storing glucose (a simple sugar that is broken down from food) in the muscles, liver, and fat cells, for later use when needed.
To recap, the beta cells in your pancreas monitor your blood sugar level every few seconds. When your blood glucose rises after you eat, the beta cells release insulin into your bloodstream. Insulin acts like a key, unlocking muscle, fat, and liver cells, so that glucose can penetrate them. Once inside, the cells convert glucose into energy to use right then, or store it to use later.
As glucose moves from the bloodstream into the cells, blood sugar levels start to drop. The beta cells in the pancreas can tell this is happening, so they slow down the amount of insulin they are making. At the same time, the pancreas slows down the amount of insulin that it's releasing into the bloodstream. When this happens, the amount of glucose going into the cells also slows down.
After you haven't eaten for a few hours, your blood glucose level drops, and your pancreas stops producing insulin. Alpha cells in the pancreas begin to produce glucagon, signaling the liver to break down stored glycogen and turn it back into glucose. This glucose then travels to your bloodstream to replenish your supply until you are able to eat again.
Insulin resistance has become an increasingly common condition in current society and causes the cells in the body to stop responding to insulin. This results in the body producing even more insulin, in an effort to increase the possibility of glucose absorption. This condition eventually may result in high blood sugar, because the insulin cannot move glucose into your cells, and is linked to obesity, inflammation, type 2 diabetes and heart disease. Although more research is needed, insulin resistance may be linked to carrying excess weight and to a lack of exercise.
Insulin sensitivity can be thought of as the opposite of insulin resistance. It means that your cells are having a healthy response to the insulin being produced in the body. By following The Livy Method, you are already actively focusing on habits that will help improve insulin sensitivity, such as:
Regular exercise and moving your body
Research supports that exercise, at both high and moderate intensities, that increases your heart rate and breathing, results in your muscles using more glucose from the body (Landes, E., & Jones, J., 2022, January). Over time, this can lower your blood sugar levels and also makes the insulin in your body work better. You will also receive these benefits for hours after your activity or workout.
However, strenuous exercise can sometimes increase blood sugar temporarily after you stop exercising, and very intense exercise can cause the body to make more stress hormones which can lead to an increase in blood sugar, as well as stress on the body. This can also help explain one of the reasons why over exercise is not a good weight loss tool! We will be discussing this further down when we discuss the hormone cortisol.
Improve your sleep habits
Not getting enough sleep, or not getting quality sleep, is linked to obesity and insulin resistance.
According to the Sleep Foundation, sleep can both raise and lower glucose levels. Our bodies experience a cycle of changes every day, called a circadian rhythm, which naturally raises blood sugar levels at night and when a person sleeps. These natural blood sugar elevations are not a cause for concern.
Restorative sleep however, may lower elevated blood sugar levels by promoting healthy systems. Decreased sleep is a risk factor for increased blood sugar levels. Even partial sleep deprivation of only 1 to 2 hours in a night, increases risk of insulin resistance, which can in turn increase blood sugar levels. As a result, a lack of sleep has been associated with diabetes.
More research is needed to better understand the connection between sleep and blood sugar. However, the following factors have been found to influence the relationship between sleep and blood sugar levels (Sleep Foundation. Retrieved March 30, 2022):
The amount of time a person sleeps (7-8 hours has been discussed as ideal).
The stages of sleep a person experiences.
The time of day of a person sleeps (considerations for shift workers).
Age (as people age they often have more difficulty sleeping).
Eating habits (for example eating before sleep and poor nutrition, which overlaps with nutrition and sleep).
Why Does Sleep Affect Blood Sugar? Researchers are beginning to uncover why sleep affects blood sugar and which underlying mechanisms are involved. So far, they’ve learned that the following physiological factors play a role in the relationship between sleep and blood sugar:
Cortisol (the stress hormone) is increased by sleep deprivation and increases glucose.
Insulin sensitivity is reduced by sleep deprivation and impacts glucose.
The time of day a person sleeps impacts insulin and cortisol levels, both of which affect glucose.
Increases in growth hormone accompany glucose increases during sleep.
Oxidative stress and inflammation are increased by sleep deprivation and impact glucose.
C-reactive protein (CRP) and other inflammatory markers are increased by sleep deprivation and can impact glucose.
Following The Livy Method Food Plan helps regulate insulin
Eating a diet which includes protein, as well as healthy fats from nuts, avocados and good oils like extra-virgin olive oil, and eating a diet rich in carbohydrates that are known to keep blood sugars stable and are high in fiber, such as whole grains, fruits, legumes, and includes many vegetables, may help reduce insulin resistance. Decreasing your intake of saturated and trans fats may also help.
Maintain a moderate weight
In people that are overweight, healthy weight loss and weight management may improve insulin sensitivity.
Leptin is a hormone made by the fat cells that creates the feeling of “fullness” that works by telling your hypothalamus, the portion of your brain that regulates appetite, that you’re full. It works in conjunction with the hormone ghrelin that increases appetite, and also plays a role in body weight.
Of the two hormones, leptin appears to have a greater influence in our body’s energy balance. Some researchers even think that leptin helps regulate ghrelin.
In general, the more fat you have, the more leptin is in your blood. However, the level varies depending on many factors, including when you last ate and your sleep patterns.
However, people with obesity may experience leptin resistance. This means the message to stop eating doesn’t reach your brain, eventually causing you to overeat. In turn, your body may produce even more leptin until your levels become elevated. The concept of this is very similar to that of insulin resistance.
The direct cause of leptin resistance is unclear, but it may be due to inflammation, gene mutations, and/or excessive leptin production, which can occur with obesity.
Inflammation is a big component of this phenomenon, according to endocrinologist Scott Isaacs, MD (McCulloch, M., 2015). Leptin resistance (as well as insulin resistance) is caused by fat cells, especially in visceral or belly fat, producing large numbers of inflammatory chemicals or cytokines, which block the effects of leptin. Eating healthful foods, including ones rich in anti-inflammatory antioxidants and omega-3 fats, can improve leptin resistance.
Although no known treatment exists for leptin resistance, a few lifestyle changes may help lower leptin levels. Here are a few tips that may help and all recommended by The Livy Method. As you will notice reading through the discussion of all the hormones and neurotransmitters, the tips will all come to be quite repetitive!
Maintain a healthy weight
Because leptin resistance is associated with obesity, it’s important to maintain a healthy weight. Additionally, research suggests that a decrease in body fat may help reduce leptin levels. Like insulin resistance, and recommended above, reducing abdominal/visceral fat can greatly help reduce the inflammation that may contribute to leptin resistance.
Improve your sleep quality
Leptin levels may be related to sleep quality in people with obesity. Although this association may not exist in people without obesity, there are numerous other reasons to get better sleep.
Research links regular, consistent exercise to a decrease in leptin levels.
The hormone ghrelin, is essentially the opposite of leptin. It’s one of the primary and most powerful hunger-stimulating hormones involved in regulating hunger. It is produced and secreted from the stomach lining, that sends a message to your hypothalamus indicating that your body needs food. The main function of ghrelin appears to be to stimulate an increase in appetite. But some researchers believe that ghrelin is not as important in determining appetite as once thought (Magee, E., & Nazario, B., n.d.). They think that its role in regulating body weight may actually be a more complex process.
Normally, ghrelin levels are highest before eating and lowest after a meal, and appear to cycle through about every 4 hours. German researchers have suggested that ghrelin levels play a big role in determining how quickly hunger comes back after we eat. Normally, ghrelin levels go up dramatically before you eat, which signals hunger. They then go down for about three hours after the meal.
Eating at regular intervals is in sync with this cycle, but after overnight fasting, ghrelin levels are increased. Ghrelin levels rise approximately two times immediately before a meal, and then decrease to their lowest levels about one hour after a meal.
Ghrelin is a short-acting hormone, and it appears that there is not a limiting level, that just builds until you eat. Importantly, it doesn’t seem to be affected by what you ate yesterday! Thus, it is important to eat when you are hungry, and not let these levels build too high, which may reinforce overeating as recommended by The Livy Method!
Although one might think that ghrelin levels are higher in an obese person, thus driving more hunger, the opposite is true. Human studies have found that ghrelin levels actually are lower in the obese, but they're more sensitive to its appetite-stimulating effects. This increased sensitivity may lead to overeating.
Tips to manage ghrelin levels
One reason weight loss can be difficult is that restricting calories often leads to increased ghrelin levels, leaving you hungry. Additionally, metabolism tends to slow down and leptin levels decrease. The Livy Method reinforces feeding into these hunger cues thus preventing ghrelin levels from getting too high, and also giving your body what it needs! This is why it is important to eat when you are hungry!
Maintain a moderate body weight
Obesity may increase your sensitivity to ghrelin, ultimately increasing your appetite.
Try to get good quality sleep
Poor sleep may lead to increases in ghrelin, overeating, and weight gain.
Because ghrelin levels are highest before a meal, listen to your body and eat when you’re hungry and then just eat to satisfaction! These are all fundamental principles of The Livy Method!
Cortisol is known as the stress hormone and is produced by your adrenal glands, as discussed previously in the science post Issues With Digestion.
To recap, during times of stress, the release of cortisol, alongside the hormone epinephrine (also known as adrenaline) engages our sympathetic nervous system, which is commonly called the “fight or flight” response. This is so our bodies can fight the emergency!
While it’s important for your body to release cortisol in dangerous situations, chronic high levels may lead to many health issues, including heart disease, diabetes, low energy levels, high blood pressure, sleep disturbances, and weight gain.
Certain lifestyle factors, which include inadequate or poor sleep habits, chronic stress, and an unhealthy diet, may contribute to high cortisol levels.
Importantly, obesity appears to raise cortisol levels, but high levels may also cause weight gain, creating a negative feedback loop, reinforcing the body’s need to store fat!
Here are how strategies recommended by The Livy Method may help manage cortisol levels:
Chronic sleep issues, including insomnia, sleep apnea, and irregular sleep habits (like those of shift workers), may contribute to high cortisol levels. Focus on developing a regular bedtime and sleep schedule may help with lowering cortisol levels!
Cortisol levels temporarily increase after high intensity exercise, but regular exercise generally helps decrease levels by improving overall health and lowering stress levels. However, stressing the body with strenuous exercise or over exercising may have the opposite effect, and in fact increase cortisol levels.
Research suggests that regularly practicing mindfulness lowers cortisol levels (Landes, E., & Jones, J., 2022, January). Try adding meditation and other relaxation techniques to your daily routine. Epsom salt baths are also a great way to relax as the warmth and the magnesium in the Epsom salts, relaxes muscles, helping to decrease stress, and ultimately cortisol levels!
Maintain a moderate body weight
Because obesity may increase cortisol levels and high cortisol levels can cause weight gain, maintaining a moderate weight may help keep levels in check.
Eat a balanced diet
Research has shown that diets high in added sugars, refined grains, and saturated fat may lead to higher cortisol levels. Following a plan like The Livy Method may help lower cortisol levels.
Estrogen is a sex hormone responsible for regulating the female reproductive system, as well as the immune, skeletal, and vascular systems. Although estrogen is also present and is an important hormone for males as well!
Levels of this hormone change during life stages such as pregnancy, nursing, and menopause, as well as throughout the menstrual cycle. For men as testosterone declines with age, estrogen levels increase.
High levels of estrogen, which are often seen in people with obesity, are associated with an increased risk of certain cancers and other chronic diseases.
Conversely, low levels, typically seen in women with aging, perimenopause, and menopause, may affect body weight and body fat, therefore also increasing risk of chronic diseases.
Individuals with low estrogen levels often experience an accumulation of weight around the abdomen, which should now be a familiar concept. This metabolic visceral fat, can lead to other health problems which should also sound familiar, such as high blood sugar, high blood pressure, and heart disease.
By following The Livy Method, you will naturally keep estrogen levels stable by doing the following:
Try to manage your weight
Weight loss or maintenance may reduce the risk of heart disease due to low estrogen levels in women ages 55–75. Research also supports healthy weight maintenance for reducing chronic diseases in general.
Low estrogen levels may decrease levels of energy that may affect your motivation for exercising. However, regular exercise is still an important aspect of maintaining health.
Follow a healthy diet like The Livy Method
Diets high in processed foods, sugar, and refined grains have been shown to increase estrogen levels, which may raise the risk of chronic disease. Limiting these foods increases the likelihood of reversing some of these health issues.
Neuropeptide Y (NPY) is a hormone produced by cells in your brain and nervous system that stimulates appetite and decreases energy expenditure in response to prolonged fasting or stress.
Because it may stimulate eating, NPY is associated with obesity and weight gain.
NPY production is activated in fat tissue and may increase fat storage and lead to abdominal/visceral weight gain and metabolic syndrome, a condition that can increase the risk of chronic diseases.
Research has shown that NPY’s mechanisms that lead to obesity may also increase inflammation in the body, further worsening health conditions.
Here are some tips for maintaining healthy levels of NPY:
Some studies suggest that regular exercise that increases your heart rate and rate of breathing may help decrease NPY levels, though research is mixed.
Eat a nutritious diet, like The Livy Method
Although more research is needed, a diet high in fat, processed foods, and added sugars may increase NPY levels. Following a nutrition food plan like The Livy Method may help lower NPY levels!
Glucagon-like peptide-1 (GLP-1) is a hormone produced in the digestive system when nutrients enter the intestines. This hormone also plays a major role in keeping blood sugar levels stable and making you feel full.
Research suggests that people that struggle with obesity may have issues with GLP-1 signaling.
Here are some tips to help maintain healthy levels of GLP-1:
Eat plenty of protein
Adding in protein rich foods have been shown to increase GLP-1 levels. The good news is that protein is an important part of The Livy Method, as it is highlighted in breakfast and dinner, but also an important component in almost all meals and snacks!
Consider taking probiotics
Preliminary research suggests that probiotics may increase GLP-1 levels, though more human research is needed. These are recommended along with prebiotics (to feed these good gut bacteria!) as part of The Livy Method supplements list!
Like GLP-1, cholecystokinin (CCK) is a satiety hormone produced by cells in your digestive system after a meal. It has an important role in energy production, protein synthesis, digestion, and other bodily functions. It also increases the release of the fullness hormone leptin which we discussed earlier.
People that struggle with obesity may have a reduced sensitivity to CCK’s effects, which may lead to chronic overeating, similar to the hormone ghrelin. In turn, this may further reduce CCK sensitivity, creating a negative feedback loop, and a cycle of overeating, worsening the likelihood of increased weight gain.
Here are some tips for maintaining healthy levels of CCK:
Eat plenty of protein
Some research suggests a diet high in protein may help increase CCK levels, and therefore help increase feelings of fullness.
While research is limited, some evidence supports regular exercise for increasing CCK levels.
Peptide YY (PYY) is another gut hormone that has a role in decreasing the appetite, leading to increased feelings of satiety. PYY levels may be lower in those that struggle with obesity, and may lead to an increase in appetite and overeating. Maintaining sufficient levels are believed to play a major role in reducing food intake and decreasing the risk of obesity.
Here are some ways to promote healthy levels of PPY in your body:
Following a well-balanced diet like The Livy Method
Eating a well-balanced diet that includes protein, fruits and vegetables may promote healthy PYY levels and fullness. Although more research is needed.
While research on exercise and PYY levels is conflicting, staying active and moving your body is generally beneficial for health, well-being and stress management!
Interconnected with the hormones involved in satiety and hunger are neurotransmitters, one of which includes dopamine. Dopamine has a direct effect in activating the reward and pleasure centers in the brain, which can affect both mood and food intake.
Those that struggle with obesity often have a blunted dopamine pathway because of chronic exposure to highly palatable foods, such as foods that are high in added sugar and fats. This over-exposure, which leads to a blunted response when eating, has been suggested to contribute to increased reward-seeking behavior, including overeating.
Eat a breakfast that is high in protein
What is breakfast?
Breakfast is unique because it breaks a time of fasting (after a night of sleep). You are considered a breakfast eater if you eat your first meal of the day following your longest period of sleep, within 2 to 3 hours of waking and if your meal contains food or beverage from at least one food group. This is why The Livy Method recommends eating within 2.5 hours of waking if you are active once awake.
Eating a breakfast that is high in protein has been shown to be one of the best methods of reducing post meal cravings and increasing dopamine levels, but also decreasing a blunted response to it. Protein contains amino acids, several of which are the building blocks of dopamine. Thus, increasing protein consumption has been suggested to increase the production of dopamine in the body!
In addition, getting enough of one amino acid, tyrosine, is an important component in the production of dopamine. Top tyrosine sources include meat, poultry, eggs, fish, cheese, soybeans, and peanuts.
There is also compelling data that shows improved satiety and reduced appetite with the consumption of a high-protein breakfast in normal-weight individuals!!!
Should you eat breakfast?
In the past, skipping breakfast has been associated with weight gain.
However, there is evidence showing that recommendations to eat or skip breakfast have no effect on weight gain or loss (Bjarnadottir, A, 2017, June).
That being said, eating breakfast may be a good idea for other reasons. It may improve mental performance in school children, teenagers and certain patient groups. Although, this may also depend on the quality of the breakfast, and as discussed, a high protein breakfast can prove to be very beneficial!
Protein activates the body’s signals that curb appetite, which reduces cravings and overeating, mostly due to a decrease in the hunger hormone ghrelin and a rise in the fullness hormones peptide YY, GLP-1 and cholecystokinin. Interestingly, several studies have now demonstrated that eating a high-protein breakfast changes these hormones throughout the day!
Breakfast eaters tend to have healthier habits
Many observational studies show that breakfast eaters tend to be healthier, and are less likely to be overweight/obese, and have a lower risk of several chronic diseases. This is mostly likely because those that put the time and energy into having breakfast, also tend to place importance on prioritizing their health in other ways.
A high protein breakfast has been shown to benefit muscle health and to support weight loss by increasing muscle mass, energy expenditure (calories burned), satiety hormones, glucose regulation and by decreasing the desire to snack at night .
Eating a high protein breakfast, has also been shown to improve the body’s response to foods high in carbohydrate, up to 4-hours after the breakfast meal. A study looked at the effect of a high protein breakfast compared to a high fat or high carbohydrate breakfast on the body’s ability to control glucose and insulin, following the consumption of white bread, four hours after the breakfast meal. Participants consuming a high protein breakfast had improved blood sugar control and insulin levels after consuming the white bread!
This all further reinforces that starting your day with a breakfast making protein the star of the show, not only helps to reduce cravings, improve the feelings of satiety, but also may help boost your mood and improve mental performance at the start of the day!
Seek pleasure from other activities
The classic approach of finding an alternate activity to get your mind off a craving has benefits beyond distraction. Activities such as listening to music and doing yoga also increase dopamine levels, and can also feed into feeling good!
Consume omega-3 fats
Omega-3 fats, by supplementation and included from foods rich in Omega 3 fats such as salmon and other fatty fishes, can increase the number of dopamine receptors and dopamine levels. Omega-3 fats also are anti-inflammatory and may help improve leptin sensitivity. Because of all the benefits they have, Omega 3 supplementation is also recommended as part of The Livy Method basic supplements list!
Now that we’ve discussed some of the important hormones and neurotransmitters involved in our hunger and feelings of satisfaction, let’s complete our discussion of digestion with a short synopsis of how long it takes the average person to actually process, digest, and move food through their body.
Breaking down digestion speed
Why is it that after eating certain foods, you can feel full for hours, but after others, you’re looking for a snack within minutes?
How long does food take to digest?
The entire digestive process can take several hours. Food generally stays in your stomach between about 40 to 120-plus minutes. Then add another 40 to 120 minutes for time spent in the small bowel. The denser the food, composed with protein and/or fat, the longer it takes to digest. It can take about 24-36 hours for digested food to be eliminated from the body. Longer in those that have digestive issues.
Simple carbohydrates, such as plain rice, pasta or simple sugars, average between 30 and 60 minutes in the stomach, but with added proteins and fats, can take upwards of between two to four hours to leave your stomach.
How long does it take water to digest?
Liquids leave the stomach faster because there is less to break down:
Plain water: 10 to 20 minutes.
Simple liquids (clear juices, tea, sodas): 20 to 40 minutes.
Complex liquids (smoothies, protein shakes, bone broths): 40 to 60 minutes.
Please note that these times are estimates and how long it takes to digest food varies on factors depending on body type, metabolism, medications, the types of food you eat, level of physical activity overall exercise fitness, if you are living a sedentary versus physically active lifestyle, past surgeries you’ve endured, and stress level.
Is it possible to tell when your stomach is empty?
Just because you feel hungry doesn’t mean your stomach is empty. Our hunger cues, as discussed, can be hormonally regulated, so if you have a high level of hunger hormones circulating, you may feel hungry, even if your stomach is full. Your perception of these sensations is also highly individual, but as discussed before, journaling, using a hunger scale, asking yourself the 4 questions, and following the Livy Method as designed, will help you become more in tune with your hunger and feelings of satisfaction when eating just enough.
Hopefully you all enjoyed this post as we continued to build upon our knowledge of hormones involved in digestion and weight loss! Stay tuned for our next science post where we will be discussing the science of fat and fat loss.
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