What is ghrelin? What does ghrelin do? How does it work? How does ghrelin help in some contexts and harm in others? What are the consequences of not knowing about ghrelin? How can you make ghrelin your well-being ally?
What is ghrelin?
Ghrelin plays a central role in regulating our hunger levels, energy storage and expenditure, and sleep cycle. Ghrelin seems, mostly, to be the hormone that stimulates hunger. As with many hormones, ghrelin has acquired its own epithet: “the hunger hormone”.
Ghrelin is a peptide hormone, one of a class of hormones that have shorter amino acid chains than protein hormones. Ghrelin is mostly created by cells that exist for the purpose of stimulating hunger, known as pancreatic polypeptide somatostatin receptor cells or P/D1 cells. Those cells are situated in the ideal place: our stomach lining.
What does ghrelin do – and how does it work?
Ghrelin drives and regulates our appetite
It acts as a communicator. When our blood sugar level drops and/or our stomachs are empty, ghrelin is released into our bloodstream, by the P/D1 cells. It travels to our brain, where ghrelin is thought, to act mainly on the hypothalamus, and somehow creates the motivation for food.
“Somehow” is used deliberately; quite how each stage in that process operates is, at best, only partially understood. We do know that ghrelin works on the brain by slotting into specific receptors, growth hormone secretagogue receptors (GHS-R), situated mostly in our hypothalamus, and pituitary gland. How the process works from then on is not so clear.
Energy metabolism
Ghrelin also influences energy metabolism. It stimulates the release of growth hormone, which plays a role in muscle growth and fat burning.
Growth hormone is produced by the pituitary gland in the brain. It influences and regulates growth, development, and metabolism. Specifically, the growth hormone triggered by ghrelin has the following effects:
- Increases fat burning. Known as lipolysis – the process of breaking down lipids, the fatty compounds in our bodies. Growth hormone promotes the breakdown of fat for energy.
- Increased protein manufacture. Growth hormone stimulates and enables the production of muscle. That requires energy, and the extra energy demand increases our resting metabolic rate, which burns calories even while we are resting. Even after the new muscle has been created, to maintain it, our bodies have to expend energy, which raises our resting metabolic rate.
- Decreased glucose uptake. Growth hormone appears to reduce our body’s use of glucose, which in turn leads to more fat having to be burned.
Energy storage
Additionally, ghrelin may affect how our bodies store energy, although that potential process is, to my knowledge, still not understood.
Microbiome health
Ghrelin may also influence, or even control, the growth and function of our gut bacteria. In previous articles, we explored how our gut microbiome is central to our digestive processes, nutrient absorption, immune system strength, mental health, and thus, our overall well-being.
While the study of the microbiome is in its infancy, and we are massively ignorant of its workings, here are some of the most likely explanations of the role of ghrelin.
Ghrelin may directly regulate or at least influence our gut bacteria, affecting their growth, survival, and metabolism. Ghrelin may be stimulating and protecting beneficial bacteria while suppressing the growth of their harmful cousins. It seems that ghrelin can also improve nutritional bioavailability by enabling the breakdown of complex carbohydrates and proteins. See the recent Psychreg article on bioavailability.
Ghrelin may be influencing the movement of food through the digestive tract, known as motility. Changes in gut motility, perhaps caused by ghrelin, may impact the environment in which our gut bacteria live, thus influencing their composition and function.
Ghrelin may also help to regulate our gut barrier, the protective layer, which separates our digestive tract from our bloodstream. If our gut barrier is healthy, it prevents harmful substances from entering the body. It also protects the balance of the gut microbiome.
Sleep regulation
Ghrelin levels fluctuate and influence our sleep-wake cycle, known as the circadian rhythm, in conjunction with other hormones such as melatonin and cortisol. Ghrelin levels tend to be higher in the evening, seem to contribute to the feeling of sleepiness and appear to increase the desire to eat before going to bed.
Both too much and too little ghrelin can be disruptive of sleep. When the balance is right, ghrelin appears to be able to outweigh decreased melatonin levels (caused by light exposure), allowing us to fall asleep on time even when there is light.
Ghrelin levels can be disrupted by: eating a large meal or snacks with high sugar content; stress; obesity and diabetes; and various gastrointestinal disorders. There seems to be a vicious cycle at work for some people: disrupted ghrelin levels cause sleep disturbance, which causes even more disruption to ghrelin levels, which further disrupts sleep, and so on.
As with any hormone, when it is out of balance, all sorts of problems can follow. Too much ghrelin is linked to obesity: ghrelin possibly causes more intense or more frequent sensations of hunger, making it more difficult to control food intake. Through that mechanism, ghrelin imbalance may indirectly cause type 2 diabetes (insulin resistant diabetes).
That knowledge in itself can cause problems: when some people learn that ghrelin is the hunger hormone, they abdicate responsibility for their eating and become even more unhealthy.
What are the consequences of not knowing about ghrelin?
If ghrelin levels are not assessed in the diagnosis and treatment of eating disorders, individuals may be administered ineffective or even inappropriate treatments. Sleep quality can be impacted, too, by a lack of awareness of the hormonal drivers of sleep. Equally, those who are not aware that ghrelin drives their hunger pangs, and that they have a choice whether to act on those signals or ignore them, to deliberately drive the body into fat burning mode, can find themselves unable to manage their weight.
How can you make ghrelin your well-being ally?
We have no direct control over our ghrelin levels. But we can take steps to create healthy ghrelin levels. Most of what we can do to maximise our ghrelin health are the same methods we can use to maintain our health more generally:
- Choose a healthy, balanced diet.
- Keep stress levels low.
- Take regular exercise.
- Minimise alcohol consumption.
- Get enough good-quality sleep.
Knowledge of ghrelin helps us to understand our eating urges; by knowing that there are biochemical processes at work that can influence our decisions.
Ghrelin is a little bit like the mythical Gremlin. As soon as we give it the wrong things (stress, sleep deprivation, alcohol, eating late at night, sugary snacks, etc.), it turns into a monster that sets in train a chain of events that can damage our well-being.
As long as we treat it well, it will be our ally. It will work its magic without any awareness on our part for life.
