how the brain gut-axis in anorexia influences hunger and fullness

You have just eaten, but your stomach is still rumbling? You feel physically full, but the urge to eat remains? Do you have trouble perceiving hunger and satiety correctly? Hunger and satiety in recovery can be a rollercoaster ride and incredibly frustrating. But the good news is, you are not alone and there is nothing “wrong” with your body. In today’s blog post, I will explain the current findings on the brain-gut-axis in anorexia and how this knowledge can help you better understand and accept changes in recovery.

hunger, fullness and the brain-gut-axis

Let’s begin by examining the fundamental mechanisms of food intake and cessation. Appetite acts as a sign of the initiation of eating and is linked to a cognitive feeling that is connected to a preference for specific types of food. Fullness, on the other hand, indicates the end of a meal with the commencement of a fullness sensation. Hunger is caused by a need for calories, whereas satiety curbs the desire for a new meal. After consuming a meal, one feels contentedly satisfied and no longer has any appetite.

The gut-brain axis facilitates communication between these mechanisms and regulates the biochemical and neural processes in the hypothalamus – a part of the brain – that controls hunger and satiety. Therefore, under normal conditions, we are able to carefully match our energy intake with energy expenditure without counting calories, restricting, or weighing. An efficient regulatory system already exists, and our body can communicate exactly what it needs. If your body is in balance, then you won’t have to worry about long-term appetite leading to continuous food intake.

Explanation of the gut-brain axis and its importance for bodily communication

The gut-brain axis is a complex communication system that describes the connection between the digestive tract (gut) and the brain (central nervous system), specifically the hypothalamus. It is believed that energy intake in the hypothalamus is controlled by peripheral signals, i.e. signals from body tissues and organs that convey information about energy and fat status. In the hypothalamus, these inputs are converted into neural and behavioural responses, which, in turn, regulate food intake and metabolism.

There are three types of peripheral signals – signals from the body tissue and/or organs that trigger neural activities in the hypothalamus and thus stimulate hunger/satiation.

Short-term Signals
– Stomach hormone Ghrelin (hunger signal),
– Small intestine peptide Cholecystokinin (CCK; meal-related satiety signal).

Mid-term Signals
– Hormone PYY3e36 synthesized in the colon, which inhibits appetite between meals,
– Plasma concentrations of nutrients.

Long-term Signals (produced by adipose tissue and pancreas)
– Hormone Leptin, which serves to maintain the body’s fat content constant,
– Pancreatic hormone insulin, which not only regulates blood sugar levels, but also together with Leptin regulates long-term body weight,
– Other energy signals.

The illustration from Meguid & Laviano (2008) demonstrates that short-term, medium-term, and long-term signals are transmitted to the hypothalamus, where two distinct paths come into play. Depending on the hormone or peptide, these paths act on behavioral reactions, leading to either the “appetite cycle” or the “satiety cycle.” In the “appetite cycle,” the messengers Neuropeptide Y and AgRP are produced, which increase appetite and lead to a desire for food. Peripheral signals such as ghrelin, the hunger signal, activate this path. The “satiety cycle,” on the other hand, is triggered by signals that indicate saturated food intake. The precursor protein POMC is broken down into various neurotransmitters and hormones, including alpha-melanotropin, which promotes the feeling of satiety. When this path is activated, it leads to a decreased appetite and an increased feeling of satiety. This information provides valuable insights into the complex mechanisms involved in regulating appetite and satiety in the body.

These two pathways interact and work together to control the balance between hunger and satiety. The NPY/AgRP pathway stimulates appetite, while the POMC pathway promotes feelings of fullness. Depending on the signals received by the body, one of these pathways will be dominant and therefore influence whether we feel hungry or satiated.

If you’re feeling overwhelmed by all the scientific jargon, don’t worry – I’ve got you covered! It all comes down to a part of our brain called the hypothalamus, which helps regulate the amount of food we eat by constantly monitoring how much energy our body has. This process involves different body parts like the mouth, intestines, liver, and fat tissue, and certain substances produced by our brain and digestive system that affect our appetite and metabolism. The special cells in the hypothalamus process all this information to influence our eating behavior.

Our body has a sophisticated and complex system to regulate food intake and optimize energy balance. In fact, strict diets, starvation or compensation is not required as we do not need to intervene from the outside. Doing so would throw the system off balance.

Several disruptions of the brain-gut-axis in anorexia

The disrupted nutrition, lack of nutrients, and psychological and physical stress in AN (anorexia nervosa) can impair normal communication and interaction between the gut and brain, leading to dysregulation of the gut-brain axis. Specifically, this can have the following effects:

1. Increased ghrelin levels (hunger signal): Elevated ghrelin levels have been found in patients with AN. This can be thought of as an adaptive response to encourage the body to take in more energy and nutrients, as it cannot withhold energy deficits and nutrient deficiencies in the long term. It has also been found that ghrelin levels do not drop after a meal as they do in healthy individuals. However, ghrelin levels tend to normalize after refeeding. This aspect is especially interesting for those who experience extreme hunger as hunger becomes more regulated and “normal” again.

2. PYY is a hormone in the body which controls appetite, and is secreted during the time between meals. In individuals with Anorexia Nervosa, PYY levels in the bloodstream can be either increased, normal, or reduced. This may result in the person’s body responding differently to food, ultimately affecting their appetite. Additionally, even if someone with anorexia has gained some weight, their PYY levels may not fully regulate, making it difficult for them to develop typical eating behaviors.

3. CCK affects how the stomach feels after eating and helps signal when someone is full. Some studies have shown that CCK levels in people with anorexia may be elevated at rest or after eating. However, other studies suggest that CCK function in anorexia may be similar to or even lower than in healthy individuals. This means that the way CCK functions in the body may be complex and vary from person to person in those with anorexia, which may explain why not everyone experiences extreme hunger during recovery.

4. In cases of anorexia, leptin levels in the body are low. Leptin is a hormone that tells our body how much fat we have and how much we should eat. When someone eats a little, leptin levels decrease, and it can cause the body to conserve energy. People with anorexia often have low leptin levels in their blood because they eat little and have little body fat. Interestingly, despite having a low blood level of leptin, people with anorexia can have normal levels of leptin in their abdominal fat tissue. This could mean that their fat cells are distributed differently from healthy individuals. When they start eating more and gaining weight, leptin levels usually increase.

The insights into disturbances in the brain-gut-axis in anorexia illustrate how significantly disrupted nutrition, nutrient deficiencies, and psychological stress can disturb the delicate balance between our gut and brain. This disruption leads to a dysregulation of the gut-brain axis in anorexia, which subsequently affects the control of hunger and satiety.

If you're going through recovery, I totally understand that it can be tough to feel your hunger and fullness cues. It's all part of balancing the different transmitters in your body, which takes time. But don't worry, your main focus should be on giving your body the fuel and nutrients it needs while working to improve your mental health. Just trust the process and take it one day at a time. I am rooting for you!

Promoting a healthy gut-brain communication as well as hunger and satiety.

Although it’s normal for communication through the brain-gut-axis in anorexia to not function optimally during the recovery from a restrictive eating disorder, there are some things you can do to promote regulation.

A balanced diet with adequate nutrients and, most importantly, calories is crucial to supply the body with energy and normalize hormone production. This means that all foods should be allowed in your diet again and there should be no more restrictions, so that the variety of gut bacteria can grow again, which has positive effects on gut-brain communication.
Gradual weight gain is also important to find your set point. Yes, it’s uncomfortable and challenging, but it allows for potential hormone imbalances to be balanced out. Additionally, some hormones that regulate hunger and satiety are produced in the fat tissue.

Regular meals and snacks can help you maintain a steady blood sugar level and stimulate the production of digestive hormones. I recommend eating something at least every 3-4 hours.
A higher protein content in your food can lead to higher PYY levels, which improves appetite regulation between meals (but that doesn’t mean every meal has to be high in protein. Simply try to include a source of protein when possible).
Psychological support and stress management.
Moderate exercise can help with bowel movements and improve mood, but excessive physical activity can disrupt hormone levels. Especially if you are severely underweight, for a while it may be more beneficial to reduce your activity to a minimum. Later on, you can add gentle stretching and mindful walks.

Your body deserves all the time it needs to adjust to a normal eating routine, so don’t worry about rushing through it. Showing a little patience will go a long way in helping you rediscover the natural rhythm of your appetite. In the beginning, focus on eating enough to stabilize your weight. Not only will this help regulate your hunger and fullness cues, it will also put you in a better place mentally. Remember to prioritize self-care during this time!

literature

Meguid, M. M. & Laviano, A. (2008). Basics in Clinical nutrition: Appetite and its control. e-SPEN. https://doi.org/10.1016/j.eclnm.2008.06.007
Smitka, K., Papezova, H., Vondra, K., Hill, M., Hainer, V. & Nedvídková, J. (2013). The Role of “Mixed” Orexigenic and Anorexigenic Signals and Autoantibodies Reacting with Appetite-Regulating Neuropeptides and Peptides of the Adipose Tissue-Gut-Brain Axis: Relevance to Food Intake and Nutritional Status in Patients with Anorexia Nervosa and Bulimia Nervosa. International Journal of Endocrinology, 2013, 1–21. https://doi.org/10.1155/2013/483145

how the brain gut-axis in anorexia influences hunger and fullness

table of contents

hunger, fullness and the brain-gut-axis

Explanation of the gut-brain axis and its importance for bodily communication

Several disruptions of the brain-gut-axis in anorexia

Promoting a healthy gut-brain communication as well as hunger and satiety.

literature

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