The "responsible" for some uncontrollable cravings could be two small molecules produced by nerve cells in the hypothalamus, according to our partner The Conversation.
Orexins A and B, or hypocretins, in fact influence the regulation of sleep, cardiovascular and endocrine functions, the regulation of energy expenditure and thermogenesis, reward systems and mood.
The analysis of this phenomenon was carried out by Maria Asunción Martinez Brocca, Head of Endocrinology and Nutrition at the Virgen Macarena Hospital and Associate Professor of Endocrinology at the University of Seville (Spain).
You have just finished eating.
No sooner have you watched an episode of your favorite series that you are again tormented by hunger… We have all known these periods of almost uncontrollable cravings, but do you know the reason for this pressing need, the origin of these demands? physiological?
Among the key players in this dietary enigma are orexins A and B, or hypocretins: two small molecules produced by certain nerve cells (neurons) in the hypothalamus.
This important region of our brain is involved in the regulation of the autonomic nervous system and many functions such as reproduction, thermoregulation and hunger.
Although their roles were initially linked to the regulation of food, especially the stimulation of appetite, we now know that they contribute to many other effects affecting our whole body.
They influence, for example, the regulation of sleep, cardiovascular and endocrine functions, the regulation of energy expenditure and thermogenesis, reward systems and mood.
They also modulate many behaviors related to our mental and physical health, ranging from arousal and emotional changes to our sensitivity to pain.
They are still involved in diseases as diverse as narcolepsy, obesity and addiction as in our response to stress.
In addition, orexin levels are altered in mental illnesses such as depression and anxiety disorders.
They can also explain gender differences in stress response and are identified as a possible therapeutic target for their treatment.
It is this incredible versatility that will help to link our feeling of satiety to the irrepressible need to put our hands back in the candy box.
This terrible desire to come back to it ... should it be attributed only to orexins? © Daisy Anderson / Pexels
Why orexins make us want to eat more
To better understand it, we must return to their role in our diet.
The system that regulates the production of orexins is able to detect changes in energy balance and increase their levels in response to fasting in particular.
And these molecules don't work alone: they interact with other proteins involved in regulating appetite, such as leptin and ghrelin.
Leptin is a digestive hormone released by adipose tissue that regulates our fat reserves (which are a form of long-term energy storage) but also our appetite by inducing the feeling of satiety.
Ghrelin, on the other hand, is a digestive hormone secreted by the stomach just before an expected meal.
It works in the short term and stimulates hunger.
How do these two molecules work with our protagonists, namely orexins?
The regulation of energy and appetite by orexin is done through information from other areas of the hypothalamus, which records, among other things, changes in the levels of glucose, leptin and ghrelin.
Neurons of the arcuate nucleus linked to the regulation of appetite © Mewtow / Wikimedia CC0 1.0
The neurons that produce orexins are able to integrate this information and trigger a response according to the body's needs.
And, unfortunately for us, may associate food intake with a reward - Orexin A would also link it to some of the environmental factors at the origin of "craving" (this irrepressible need observed in addictions, where its role has to elsewhere also been identified) and relapse ...
A major role throughout life
But the impact of orexins is, as has been mentioned, much broader.
There are times when the urge to eat is sometimes heightened, for example during pre-menstruation or after menopause.
What is behind these physiological demands?
Again, the relationship of orexins has been investigated.
During menopause, sleep disturbances, weight gain and increased anxiety are frequently described. To try to understand the extent of their regulatory abilities, we have studied how the levels of these hormones are altered in the body and whether their variations may be associated with some of the symptoms observed. And yes, there is an increase in orexin A levels along with the reduction in estrogen levels that then occurs.
However, clinical studies performed to date are not yet conclusive and no clear association has been found between orexin A levels and other variables typical of the postmenopausal state.
These include the impact of hormone replacement therapy on these levels, changes in sleep quality and body mass index.
Recent studies suggest that orexin A levels and cognitive performance are lower in women with anorexia nervosa © Conmongt / Pixabay
Links to eating disorders
Anorexia nervosa is particularly concerned.
This eating disorder is characterized by being underweight (abnormally low weight, due to insufficient and unbalanced food intake), which results from an altered perception of body image and an intense fear of gaining weight.
This severe malnutrition affects the whole body and causes other clinical manifestations, ranging from the absence of periods to impaired brain function.
Recent studies suggest that orexin A levels and cognitive performance were lower in women with anorexia nervosa.
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In addition, low levels of this hormone have also been found to be associated with reduced cognitive flexibility and poorer psychological test scores assessing decision making in risky situations.
It remains necessary to expand and confirm these results, which nevertheless open up an interesting avenue of research linking neuropsychology and energy expenditure.
What perhaps to understand more broadly the mechanisms by which they act and interact.
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This review was written by Maria Asunción Martinez Brocca, Head of Endocrinology and Nutrition at Virgen Macarena Hospital and Associate Professor of Endocrinology at the University of Seville (Spain).
The original article was published on The Conversation website.
Declaration of interests
Maria Asunción Martinez Brocca does not work, advise, own shares, receive funds from any organization that could benefit from this article, and has not declared any affiliation other than her research organization.
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