Fasting is a practice that has been around for centuries.
Water only fasts are regularly included in many religious cultures and can occur at specific times of the year or based around prayer sessions.
A recent interest in the health benefits of fasting has led to an increase in awareness and popularity of fasting and emerging research is showing some profound benefits to health.
We are dedicated to providing insightful, evidence-based and actionable content and in this article we explore exactly how fasting supports good health.
What is fasting?
Fasting involves the abstinence from food for a set period of time – this is often called water fasting.
The rise in popularity in fasting has led to many terms being used and intermittent fasting is a common one. Intermittent fasting describes periods of eating interspersed with not eating.
We all carry out a certain degree of intermittent fasting overnight – the period when we are asleep counts as fasting.
A newer term, time restricted eating (TRE), refers to a longer overnight period of fasting – usually somewhere in between 12-16 hours.
Some forms of TRE also time food intake to align with the natural body clock – the circadian rhythm.
Intermittent fasting has also been used to describe calorie restricted eating plans like the 5:2 diet. Whilst these are not strictly ‘fasts’ they do seem to bring their own health benefits.
In this article we look at the evidence from water only fasts and TRE.
What happens during a fast?
In order to understand the health benefits of fasting it is useful to know what happens when you are fasting.
When you eat, several hormones are stimulated and in the ‘fed state’ the body is primed to use energy from food for fuel, or to store it for later use.
Around 5 hours after a meal the body enters what is called the ‘post absorptive state’ or ‘fasting state’.
During the post absorptive state the body actively uses stores of energy in the liver to provide fuel for the body.
Once these are reduced the ‘metabolic switch’ is flipped and fat is mobilised from stores to be used as fuel.
The amount of time it takes to fully move to fat burning will vary from person to person but it is generally thought that it begins at around 12 to 16 hours or more (1).
It seems that during this switch of fuels a change in hormonal balance is seen and there can be an increase in natural self-cleansing processes that have important functions within the body.
A reduction in these self-cleansing processes is linked to degenerative conditions like Parkinson’s and cardiovascular disease (2).
Health benefits of fasting
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Weight management
Over 60% of the population is thought to be overweight or obese (3) and obesity is fast becoming a global health burden.
Maintaining an optimum body weight is known to reduce the risk of several lifestyle diseases and fasting is now well known to increase fat burning and support weight loss (4).
What’s more, fasting increases visceral fat loss, which is fat from around organs in the abdominal region (5).
An increase in visceral fat is linked to increased inflammation and a variety of hormonal and inflammatory conditions.
Although fat burning may be one reason why fasting increases weight loss, there may be other mechanisms involved.
Appetite regulation may be enhanced as during fasting body cells become more responsive to the ‘satiety’ hormone leptin, known to signal that we are full.
Studies show that appetite in the evening can be reduced when a person regularly fasts (6).
There may also be an inadvertent reduction in overall calorie intake as eating within a set period of time during the day, as in TRE, naturally limits night-time eating (7).
One clear benefit of fasting versus traditional calorie restriction for weight loss is the fact that fasting helps to preserve lean muscle mass (8).
With calorie restricted diets around 25-30% of weight lost is lean muscle mass.
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Metabolic balance
One of the most common metabolic conditions is diabetes and over 3 million people in the UK suffer with Type 2 diabetes.
Keeping a healthy metabolic balance can greatly reduce the risk of associated health conditions.
Metabolic syndrome is a collection of risk factors that can significantly increase the risk of developing other conditions.
It involves high blood pressure, obesity, a change in cholesterol levels and insulin resistance.
Fasting has been shown to improve blood sugar control, regulate insulin levels and improve body cells’ response to insulin (9).
This effect can be seen independent of weight loss (10).
Improvements in insulin sensitivity during fasting may be down to an increase in a protein called adiponectin.
Adiponectin is released by fat cells and serves to regulate blood glucose levels and the breakdown of fatty acids.
A low level of adiponectin is linked to insulin resistance (11).
Although fat cells produce adiponectin, levels may be low in obesity particularly if there is a high amount of visceral fat.
This is thought to be due to cell dysfunction.
The lowered levels of adiponectin in obesity may be one of the reasons there is an associated increase in insulin resistance and Type 2 diabetes.
Fasting not only increases loss of visceral fat but increases adiponectin levels and insulin sensitivity (12).
With so many benefits to blood glucose metabolism it is unsurprising that fasting is now linked to a lowered incidence of Type 2 diabetes (13).
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Cardiovascular support
Fasting affects blood pressure in several ways and during the initial phase of fasting blood pressure can drop which may leave some people, who are not used to fasting, feeling light headed or fatigued.
This effect seems to dissipate with regular fasting.
The long term effects of fasting on blood pressure are well debated and may in part be linked to weight loss, as an increase in body weight is one factor involved in hypertension.
Several studies have shown that over the long term fasting improves both systolic and diastolic blood pressure (10, 14, 15).
Keeping a healthy blood pressure is crucial for reducing the risk of stroke.
Cardiovascular health is further supported through improvements to blood fats.
During regular fasting there is an increase in the beneficial HDL cholesterol (16) and a reduction in triglycerides (17).
In addition to this there is a lowering of homocysteine (18).
Homocysteine is a damaging intermediary amino acid that should normally be kept low in the body.
If levels are high it can cause damage to blood vessels and is linked to the development of cardiovascular disease (19).
A reduced risk of coronary artery disease is seen in regular periodic fasting (20).
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Reduced inflammation
Inflammation is a natural immune response and is important for dealing with injury and infection.
Acute inflammation is a helpful response.
Unfortunately, chronic inflammation is becoming more common and is contributing to the development of many health conditions.
During the inflammatory response specialist cells and messengers, like cytokines, are released, each having their own effects.
During fasting, high levels of inflammatory cytokines are seen to lower (21, 22) and markers of inflammation, such as C-reactive protein (CRP), are also reduced.
This may have profound implications for future heath as conditions such as arthritis, heart disease, Type 2 diabetes, obesity, inflammatory bowel disease (IBD) and depression all have an inflammatory link.
Reducing inflammation through fasting may therefore be of use for an overall reduction in the incidence of inflammatory diseases.
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Gut support
Good health begins in the gut. The complex eco-system that resides in the gut, also called the microbiome, has a vital role to play when it comes to health.
An abundance of research into the microbiome now shows that they not only support gut health and function but also influence other areas of the body.
For instance, molecules produced by bacterial fermentation of dietary fibres are known to reduce the rate of diabetes, heart disease and inflammatory conditions.
A lack of dietary fibre or an imbalance in microbial species or number in the gut (dysbiosis) can lead to an increased risk of developing chronic conditions.
Fasting is known to offer support for the microbiome and more diversity of bacterial species is seen after fasting.
In particular, levels of a bacterium called Akkermansia are increased after fasting (23).
Akkermansia are known to support the gut lining itself and have a link to improved metabolic health, including better blood glucose regulation and insulin sensitivity (24).
As the same bacteria may be low in obesity, fasting may restore levels – this may be one mechanism by which fasting improves metabolic health in obesity.
Between meals the gut completes cycles of cleansing along the lining.
Peristaltic movements, called the migrating motor complex (MMC), help to sweep the digestive tract and remove impacted debris, dead cells and harmful organisms.
If food is eaten too regularly (three meals and two snacks a day) the gut is not able to perform this internal cleanse.
The migrating motor complex slows down at night (25) and a period of fasting during the day may aid in keeping the digestive tract healthy.
This can be incorporated in a full day water fast or even in extended TRE where food is only eaten in an 8-10 hour period.
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Enhanced cellular cleansing (autophagy)
In order for body cells to perform effectively they need to be free from debris, damaged material and harmful pathogens.
Accumulation of any of these factors is linked to poor functioning which may lead to degenerative diseases.
The body’s natural self-cleansing process, called autophagy, is stimulated by a lack of nutrients and therefore fasting is one of the most potent ways to activate this process.
Frequent eating patterns and eating late into the night both inhibit cellular housekeeping.
A disrupted or dysregulated autophagy process is known to impact ageing, cancer, neurodegenerative diseases and the ability deal with infections.
There also seems to be a link between autophagy and inflammation, this is thought to be down to an influence on inflammatory cells as well as other factors (26).
This may, in part, explain how fasting reduces inflammatory markers.
Researchers studying the effect of autophagy on inflammation suggest that enhancing autophagy may prove to be a useful way to address many inflammatory conditions such as Crohn’s disease, cystic fibrosis and chronic obstructive pulmonary disease (COPD) (26).
Although research on fasting is still ongoing it is clear that it brings several health benefits.
Humans, like many mammals, are designed to experience periods without food in order to maintain health.
Perhaps it is now becoming clear that not only do poor food choices impact health but poor eating patterns can also have negative effects on health.
If you are interested in trying fasting then it can be useful to start your journey with the support of a qualified practitioner who can guide you on the most suitable way to incorporate fasting and assess any other factors that may be influencing your health.
We believe sharing knowledge and experience is an essential way to support others in achieving optimal health.
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