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Fasting is not a new phenomenon and has been around since hunter gatherer times.
Human bodies are designed to experience period of ‘feasting’ and ‘fasting’.
During times of fasting adaptations occur and certain processes are stimulated which enhance body functioning and health.
We always take an evidence-based approach and in this article we take a look at the mental health benefits that occur with regular fasting.
Defining a fast
There are a variety of different fasts and the term intermittent fasting is now commonly used.
With so much information available, there is no wonder there can be confusion surrounding fasting.
Essentially, fasting involves set periods of time without food.
This can be in a pattern like the 16:8 diet, a form of time restricted eating (TRE), or a more prolonged water only fast of 24 hours or more.
Quite often the term fast is associated with calorie restricted diets, like the 5:2 diet – although they do not involve complete restriction of food they do seem to bring many health benefits.
Adaptation during fasting
During the period of ‘feasting’ the body runs primarily on glucose from food.
Once energy needs have been met, the body very cleverly stores glucose molecules in the form of glycogen in the liver and muscles for use when food intake becomes sparse.
In the period of fasting, glycogen stores in the liver are used first to sustain the body and energy needs.
Once glycogen stores run out the body switches to using stored fat as an energy source.
The time it takes for this switching of fuels will vary from person to person and is thought to typically be around 12-16 hours (1).
During fasting there is an increase in a self-cleansing process in cells called autophagy.
This is a complex process where damaged and dangerous parts of a cells are repaired or removed.
During normal day to day functioning there is a degree of damage that occurs in cells – if autophagy is not occurring often enough there can be an accumulation of debris, tangled proteins and harmful substances.
In fact, a disrupted or dysregulated autophagy process is linked with a variety of chronic degenerative conditions including neurodegenerative conditions like Parkinson’s (2) and Alzheimer’s (3).
Fasting and the brain
- Memory and learning
Research from studies conducted in rodents is showing a clear benefit of fasting on the brain itself.
During fasting it seems that there is regulation of certain growth factors, like BDNF (brain-derived neurotrophic factor), which act on certain cells of the nervous system to encourage growth of new nerve cells and to support existing nerve cells.
BDNF has been shown to be associated with memory (4).
It is known to encourage an increase in something called synaptic plasticity – a process that allows adaptation between nerve cells and impacts their communication.
BDNF also increases the generation of new nerve cells.
Studies completed in mice show that a long term pattern of intermittent fasting gives significant improvements in learning, memory and cognitive functioning (5).
Dementia and Alzheimer’s are neurodegenerative conditions characterised by memory loss and a decline in cognitive functioning.
Over three quarters of a million people in the UK suffer with Alzheimer’s or dementia and currently there is no cure or treatment to slow progression.
Rodent studies suggest that intermittent fasting can protect the brain against age related changes and potentially protect against changes seen in Alzheimer’s disease (6).
There are many factors that may play a role in the development of dementia and poor glucose tolerance, insulin resistance (7) and metabolic syndrome (8) are now known to be associated with changes that lead to the development of Alzheimer’s and dementia.
Physical benefits to fasting include improved sensitivity to insulin, better blood glucose control and reduced blood pressure (9), all of which may explain why fasting could reduce the risk of cognitive decline.
- Mood and anxiety
Mental health disorders affect around 25% of the population and are a leading global health burden.
The development of depression and anxiety is influenced by a variety of factors and both issues may range from mild to severe.
Intermittent fasting shows an anti-depressant like effect in mice (10) and in a study of nurses fasting during Ramadan, there was a significant reduction in depression following the fasting period compared to before (11).
A reduction in symptoms of low mood and anxiety may be down to several factors
Depression is known to have a link with increased inflammation (12) and fasting and autophagy are both shown to reduce inflammation (13, 14).
The role of BDNF in depression and anxiety is interesting and several studies have shown that levels can be low in depression (15) and in depression-related suicide (16).
BDNF levels may also be low in anxiety, although some variation can be seen across different anxiety disorders (17).
Common anti-depressant medications can actually increase levels of BDNF (18).
As fasting naturally increases BDNF levels (19), it may explain why those who fast report improvements in mood, alertness and a sense of euphoria (20).
Another physical benefit of fasting is that of support for the microbiome, the complex ecosystem that resides in the gut (21).
The trillions of bacteria carried in the gut not only support gut health and digestion but can also positively influence inflammation (22) through their role in immune function.
A direct link between the gut and the brain exists and imbalances within the numbers, or types, of organisms in the gut (dysbiosis) is linked with depression (23).
Restoring the bacterial balance can be achieved through probiotics (24) and fasting (25) and may be another mechanism by which fasting supports mental health.
Although evidence from rodents is clear and the emerging research into the mental health benefits of fasting in humans is promising, more research is needed.
The mind and the body are not two separate entities and several mechanisms create a direct link between the two.
Improving physical health through fasting may also mean that mental health follows suit.
Incorporating regular fasts, through time restricted eating, or intermittent water fasts can be difficult to start with.
There may be instances where fasting may not be suitable and it can be useful to obtain guidance from an experienced practitioner.
There can be various factors involved in mental health issues and a qualified health practitioner will be able to assess factors such as hormones, nutrition, gut health and genetic susceptibility.
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