Introduction

Many of my ‘yummy mummy’ friends have taken up water fasting this year and are positively evangelical about it. As veterans of all kinds of crazy food fads, it was probably inevitable that my friends would transition from the cabbage soup diet (and such like) to water fasting for weight loss and other slightly shallow reasons (as they would willingly admit).

More recently, some of my patients have started to ask me about the health benefits and safety of water fasting.

Water fasting is a form of nutritional intervention that is said to improve metabolic dysregulation, cardiovascular risk, reduce weight and increase longevity.

Having grown up in rural Catholic Ireland, I have to admit that I associate fasting with penitence and suffering and it is quite a mind shift to envisage fasting as a positive health promoting endeavour.

Time to check the source data.

What Is Water Fasting?

Homo sapiens has been around for the last 250,000 years. The human species has evolved to survive periods of food shortages and humans have voluntarily fasted for at least the last 2,000 years. We have evolved in environments where food was scarce or seasonal and we developed innate adaptations to enable us to function at a high level (physically and mentally) even in food deprived or fasted states. We build muscle and fat during times of abundance and then re-use it during times of scarcity. That was before 24/7 convenience stores and online food delivery services.

Severe food deprivation in mammals causes a decrease in the size of most organs with the exception of the brain and the testes (1). From a Darwinian perspective, ability to master high functioning while food deprived offers a survival advantage. An interesting highly conserved behavioural trait of mammals is to be active when hungry and sedentary when full.

The hungry brain produces brain-derived neurotrophic factor (BDNF) which modulates metabolic and behavioral responses to fasting including regulation of appetite, activity levels, glucose levels and functioning of the autonomic nervous system (2)

Fasting can boost cognitive function which is not as odd or counter-intuitive as it sounds. There was a Darwinian advantage to having a sharp brain during periods of starvation as natural selection would favor the caveman who could remember where he/she stored food or how to make a plan to get food.

I am guessing that maintaining testes size had to have been important and must have had something to do with survival of the species too.

Living in a world where we can access food on a continuous basis, many people will think that they consume three meals per day. The reality may well be that they eat/snack up to 20 times per day. (Some nutritionist jokingly say that eating three meals a day with no snacking is a form of intermittent fasting in modern western culture). Overeating is just not good and is associated with metabolic dysregulation especially if overeating is combined with inactivity.

There is increasing evidence in the medical literature that the balance between energy expenditure and consumption dictates both our quality of life and our lifespan (3).

According to the Blue Zones Solution: Eating & Living Like The ‘World’s Healthiest People, a key factor in longevity is summed up in the Japanese expression ‘Hara hachi bu’. This is the Okinawan 2500-year old Confucian mantra said before meals to remind people to stop eating when their stomachs are 80% full and this habit correlates with a long healthy life. This is a form of energy restriction.

In practice, sustained caloric restriction is difficult for people (outside of Okinawa). Oddly fasting may be an easier option for some people.

Fasting is defined as a partial or total abstinence from all foods or from selected foods. Water fasting refers to fasting from all foods except water.

Fasting is often undertaken as part of a spiritual practice. Many religious traditions incorporate fasting into their rituals and fast on designated days of the week, calendar year or lunar calendar.

Perhaps the best known spiritual fast is the Islamic Ramadan which is a 28-36 day fast in which food and drinks (including water) are prohibited during daylight hours in the ninth month of the Islamic lunar calendar. Strictly speaking, Ramadan is not a water fast but is a well studied fast and as such we will look at some of the studies on Ramadan.

Greek Orthodox Christians fast for up to 200 days in a calendar year e.g. prior to Christmas, Lent and prior to the feast of the Assumption.

Another spiritually-based fast is the Daniel Fast which is based on the biblical story of Daniel (1:8-14 NIV) in which Daniel ate nothing but vegetables and water for 10-21 days.

Water fasting can be done for different lengths of time.

Intermittent Fasting

Extended periods eg 16 -18 hours with little or no energy intake with intervening periods of normal food intake on a recurring basis

Alternate Day Fasting

This involves alternating 24 hours periods of ‘feasting’ where people can consume what they wish and ‘fasting’ where they just consume water.

Periodic Fasting

Fasting for a defined time period (also known as periodic feeding)

Prolonged Fasting

Fasting for a lengthy periods eg 40 days.

Time Restricted Fasting

Limiting caloric intake to certain hours of the day (usually confining all food intake to an 8 hour period or less).

Just to be clear, fasting is different to caloric restriction which involves a chronic reduction in daily calorie intake by 20-40% but meal frequency is maintained (the Blue Zones model). Calorie restriction has been shown to extend the lifespan of rodents (4).

Starvation is a chronic nutritional deficiency that can result from extreme fasting.

Interest in fasting peaked in the UK in 1992 following a BBC documentary which featured the 5:2 diet which involves 5 days of regular eating followed by 2 days of fasting.

Therapeutic water only fasting was used in the 1960s and 1970s for the treatment of obesity but declined in use due to serious side effects including death.

Before we write off water fasting, it has to be said that some of these patients were poorly selected, fasted for excessive periods and were often inadequately monitored.

Mechanisms by which fasting can help with health involve:

activation of adaptive cellular stress response

reduction of free radicals

improved autophagy

modification of apoptosis

alteration of hormone balance

switch from the sympathetic to parasympathetic nervous system.

Some of the benefits of fasting come from reducing the intake of harmful components of the standard American diet (SAD). Other benefits come from autophagy (which will be discussed in the next section). Key benefits come from enhancing adaptive cellular stress responses.

I think it is important to explain the concept of adaptive immunity or adaptive stress responses in some more detail. Understanding this concept helps us to understand two key recommendations related to fasting which we will address and which are missed by many people who fast.

Fasting is believed to promote resistance to stress and increase our health. This means transiently stressing the body (which in the short term may have adverse effects on biological parameters including reactive oxygen species) but with the overall aim of allowing our bodies to develop new skills for dealing with stresses. Fasting improves our metabolic plasticity.

This has two implications:

Firstly, fasting for two or more days may be required to get the full benefits of fasting as we actually have to give time to allow the adaptive responses kick in.

Secondly, it may be best to avoid supplements and anti-oxidants when fasting as they may mitigate against the generation of free radicals which are needed to prime the adaptive cellular response. I never knew either of these facts until now.

Fasting is a cornerstone of naturopathy. In Ayurvedic medicine, fasting is known as ‘upavasa’ and is used to decrease diseases, increase sensory acuity and enhance digestive processes. In this article, we will present the data on water fasting but will supplement it with wealth of data from different types of fasting where appropriate.

You might reasonably think that there are no products for sale relating to fasting. (Or maybe it is only me that is quite that naive). Well, there are. In fact, Amazon can offer over 8000 products inducing books, journals and prayer cubes for people who fast.

You may ask if fasting is popular? That would be another yes. A paper published by a clinic in Santa Rosa, California states that they admit 1000 patients per year for medically supervised fasting or ‘rebooting’ and have seen a total of 10,000 patients in total since they opened (5).

Is There Any Research?

There are 576 publications relating to ‘water only fasting’ including 83 clinical trials. To put this into context, there are 3381 publications related to general fasting including 406 clinical studies.

Does Water Fasting “Create Autophagy” In The Body”?

This is another key feature of fasting that needs to be understood to get the full benefits of fasting. Autophagy is a very interesting process that occurs in the human body and is essential for cell physiology and human health. It essentially refers to intensive spring cleaning and re-cycling of cellular debris. It is an ancient human process that is highly preserved and has been implicated in the longevity of the human species. It was initially recognized in yeast as a physiological response to starvation and was a survival technique that ensured a constant supply of nutrients by recycling essential substrates.

Under normal circumstances, autophagy occurs at a baseline level in most cells. The level of autophagy increases under times of physiological stress such as fasting (6).

Autophagy involves the formation of a double-membrane structure that takes up unwanted or defective material (including pre-cancerous cells) to form what is known as an autophagasome. The autophagasome fuses with a lysosome in the cell which then degrades and recycles the macromolecules in order to maintain a supply of building blocks for cell metabolism. A convenient side effect of this process is the removal of defective cells or misshapen proteins and apoptosis (cell death). Adios to mutated cells, and ola to new raw material for new cells.

This is pretty much the same as cleaning your house. You decide what you don’t want and put it in a trash bag (autophagasome). The trash bag then goes to the recycling bin or shredder (lysosome) to create the building blocks that can be used for new products. Autophagy regulates apoptosis, inflammation, pathogen clearance and the immune response.

Xenophagy refers to autophagy that removes viruses, bacteria and parasites from the body. Interestingly, vertebrates and invertebrates exhibit decreased appetite during infections suggesting that sickness associated anorexia evolved from an evolutionary standpoint in order to trigger xenophagy (7). I am a big fan of nature’s designs.

Autophagy genes are subject to the normal circadian rhythms or biological clock that humans are subject to.

Bottom Line

Fasting increases autophagy which is a highly conserved health-promoting cell physiology activity.

Does It Lower Age Induced Inflammation?

A Lithuanian study published this year looked at the effect of a two day fast on stress, mood, brain activity, cognitive function, psychomotor function and motor function in overweight women (8).

A total of 11 women were randomly allocated to either a water fast or regular diet for 2 days

The study showed that a 2 day fast evoked a moderate stress response and a shift towards the sympathetic nervous system. Fasting did not affect mood, brain activity, cognitive, motor or psychomotor performance. The authors suggested that better aerobic endurance could increase the capacity for dealing with acute fasting.

The same investigators had done a study two years before looking at the effects of a 2 day fast in amateur weight lifters (9).

A total of 9 participants completed the 48 hour zero calorie water fast. They found that fasting resulted in higher parasympathetic activity and improved prefrontal cognition such as mental flexibility. Unfortunately, it also increased anger.

Bottom Line

Water fasting may have differential effects in different demographics and is currently not supported to reduce age related inflammation .

Does It Boost The Immune System?

A systematic review published in November 2017 showed that fasting during Ramadan had minor and transient effects on the immune system (10).

The review looked at 23 papers and included healthy individuals, people with cardiac disease, pregnant women and athletes. Each study used different methodologies and end-points which makes it difficult to provide detailed specifics apart from the general conclusion that any changes noted on the immune system were transient and returned to baseline after the fast.

Periodic 3 days cycles of fasting have been shown to increase endogenous steroid levels, reduce pro-inflammatory cytokines and promote demyelination in mice with experimental autoimmune encephalomyelitis and multiple sclerosis (11).

Another interesting concept in this field is that infections due to pathogens that produce neuraminidase can bind to lectins in food and trigger an autoimmune reaction (12). Fasting removes lectins from the equation which could theoretically reduce the risk of autoimmunity during infections. Hence the age old adage of ‘starving a fever’ may just be very wise counsel indeed.

Finally, another study done during Ramadan in 13 Muslim men aged 28-54 showed a beneficial effect of fasting on neutrophil phagocytic function (13).

Bottom Line

There is nothing specifically looking at ‘water only fasting’ and ‘immunity’ but in general there is some information to suggest that fasting can impact the immune system transienetly and to a minor degree.

Does it Reduce Oxidative Damage?

Using a vessel occlusion vascular dementia model, rats were subjected to either intermittent fasting or regular fasting for 12 weeks (14). Intermittent fasting was found to prevent vascular cognitive deficits, lower gene expression of oxidative enzymes and neuroinflammation.

The effect of water fasting on oxidative stress was studied in 10 volunteers who drank only water for 10 days followed by a regeneration diet. A Slovakian study just published this year found that complete water fasting decreased lipid peroxidation (TBARS) and that this remained stable after fasting (15).

Bottom Line

There is very limited but positive science to suggest that fasting can impact on redox reactions. As mentioned above, the effect of fasting on redox reactions may be biphasic with an initial negative effect on redox status followed by an adaptive response and a net benefit on redox status. This means that people who fast have to take into account the fact that there will be a transient deterioration in anti-oxidation status prior to an improvement and therefore fasting needs to be undertaken very carefully (if at all) in people with borderline anti-oxidation status.

Is it Good For Weight Loss?

A meta-analysis of weight loss during Ramadan showed that weight loss was relatively small and gradually returned to pre-Ramadan status (16). Average weight loss in men was -1.51kg and -0.92kg for women. Weight loss was also greater in Asian populations as compared to African and European.

Another systematic review looked at the health benefits of fasting and found 3 randomised controlled trials that showed that fasting decreased weight (17).

CNN profiled a study published last year in JAMA which compared the effects of alternate-day fasting versus daily calorie restriction on weight loss, weight maintenance, and risk indicators for cardiovascular health disease (18)

Researchers at the University of Illinois randomized 100 obese adults to:

alternate-day fasting (25% of energy needs on fast days; 125% of energy needs on alternating “feast days”),

calorie restriction (75% of energy needs every day),

a no-intervention control.

The trial involved a 6-month weight-loss phase followed by a 6-month weight-maintenance phase.

There were no significant differences between the intervention groups in terms of blood pressure, heart rate, triglycerides, fasting glucose, fasting insulin, insulin resistance, C-reactive protein, or homocysteine concentrations at month 6 or 12. Alternate-day fasting did not yield superior results in terms of weight loss, weight maintenance, or cardioprotection versus daily calorie restriction. Additionally, the drop-out rate in the fasting arm was higher than that in the daily calorie restricted arm. Participants in the alternate day fasting arm of the study tended to overeat on fasting days and under eat on non-fasting days.

Bottom Line

Data are inconsistent on the longterm effects of fasting on weight. However, this may be due to the significant differences in the types of fasting and the differences between the study populations.

Is It Good For People With Heart Disease or Diabetes?

A total of 68 patients with borderline hypertension (systolic BP > 119 and diastolic BP <91) participated in a trial on water only fasting (19). The study was well-designed. Prior to the fast, the study participants were prepped with a fruit and vegetable diet.

The study participants also had careful refeeding after the fast with a diet that was low in fat, low sodium and plant based in order to prevent a re-feeding type syndrome (see safety section).

Following a 14 day water fast, 82% of the study participants achieved a BP of </= 120/80. The greatest reductions were seen in people who had the highest baseline BP.

A study in 30 healthy volunteers evaluated the effect of a one day water only fast on a range of markers of cardiometabolic disease (20). The study used a randomized cross-over study design.

The one day fast resulted in statistically significant increases in growth hormone, hemoglobin, total cholesterol, HDL and significant decreases in triglycerides and weight. All makers returned to baseline at 48 hours post end of the fast with the exception of weight loss and triglycerides. This study does add to the positive studies on the effects of fasting on weight loss that we discussed in the previous section.

The researchers commented that further studies are needed to evaluate the effect of longer water fasts or repeated one day fasts on these biomarkers.

The systematic review discussed earlier which looked at the health impacts of Ramadan showed that Ramadan can have beneficial effects on plasma lipids (as well as oxidative profile)(10).

Bottom Line

There are some studies which show benefits of water fasting on cardiovascular risk factors but long term studies are needed to see if these benefits are sustained after fasting or between repeated fasts.

Is Water Fasting Safe?

A review just published this year assessed the tolerability of water fasting (21).

The investigators reviewed the electronic charts of 768 visits of adults who fasted for >/= 2 consecutive days. No deaths were reported. The majority of the side effects noted were mild and were known and expected side effects of fasting. Side effects included fatigue, nausea, insomnia, a headache, hypertension, syncope, dyspepsia and backpain. Only two serious adverse events were noted- an upper respiratory tract infection in one patient and hyponatremia (low sodium) in a 70 year old patient.

Despite case reports of renal stones in people who fast, a Canadian study published this year in the Journal of Urology found no increase in calcium phosphate precipitation following 18 hours of food and water deprivation (22).

Fasting is not recommended for people who are pregnant, nursing moms, children or people with diabetes or chronic diseases. People with a history of anorexia or bulimia need to take special care in order to ensure that fasting does not trigger or substitute for an eating disorder.

A potential risk associated with fasting is the re-feeding syndrome (23). This occurs following re-establishment of a normal nutritional profile in someone who has become malnourished from fasting. This should not be a significant problem in someone who fasts for just a day but can be a real problem in someone who fasts for longer or who fasts and has a baseline borderline nutritional status. The hallmark feature of the re-feeding syndrome is hypophosphotemia. Other features include electrolyte disturbances and trace element deficiencies.

It can lead to organ damage/organ failure or death. It underscores the need for a gradual re-introduction of food in people who undertake any kind of fasting. Even if people are not at risk of refeeding syndrome, care needs to be taken when starting back on food after a fast and a slow re-introduction of foods is recommended.

People with GERD (gastro-esophageal disease find that their symptoms) are easier to manage with regular food intake and may not be suited to fasting.

Fasting is something that is best discussed with the persons own physician in order to ensure that individuals are suited to fasting.

Anyone undertaking fasting should prep appropriate by having a lean green diet for some days prior to fasting, ensure adequate hydration during the fast followed by careful re-feeding. Some individuals and some fasts are best done under direct medical supervision.

Therapeutic water fasting also includes suitable physical activities, exercising, walking and hiking. Again it is best to check in with your own physician in order to assess your suitability to fasting, to design an optimal fast for you and to monitor your progress during the fast and re-feeding periods.

Conclusion

Water fasting has its proponents and opponents. It has been used since ancient times for cleansing, spiritual renewal and health benefits.

Anytime, I research an article for Health But Smart, I try out the product or technique myself in addition to doing the academic research part. I embarked on a three day fast (following medical clearance). I prepped with a clean green diet and then began my water fast.

Day 1 – I was fine until lunchtime. I had to attend a journal club at lunchtime and lunch was provided. The presentation (and presenter) were mind-numbingly boring and I found myself considering some nibbles to allay the boredom (but I didn’t). That evening I was giving a talk and was really enjoying myself and completely forgot that I was fasting.

Day 2- I was a little hungry all day but it was totally manageable until I was cooking family dinner or food shopping. I began to lust after a fillet steak in the meat section when shopping which is odd as I am a very happy vegetarian.

Day 3 – I woke up looking forward to finishing the fast and having the moral victory of a three day fast. I had forgotten that it was Mother’s Day and the kids decided to surprise me with breakfast in bed.

Firstly, a 7 years old idea of ‘treats’ would not be my idea of great food and certainly wouldn’t have been in the list of approved foods for refeeding (think chocolate-covered strawberries and an oreo milkshake).

Secondly, it underscores the importance of planning fasting. Our regular social interactions frequently revolve around food and fasting should not become a deterrent to wholesome, healthy relationships enjoyed with food.

Even though, I really wanted to continue my fast, I devoured the sugar laden food to the delight of my kids. I did wonder if the biological stress of the oreo milkshake would add to my adaptive cellular response or completely offset any health benefits from 60 hours of water fasting.

I have to admit to a feeling of achievement having mastered fasting for the 60 hours. Having reviewed the basic science and published literature on fasting, I will likely do another water fast in the near future and will certainly keep an eye on the literature for new studies relating to fasting.

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