Intermittent Fasting

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Intermittent Fasting

What is Intermittent Fasting (IF)?

Berardi (2011) describes intermittent fasting as the practice of occasionally going for extended periods of time without eating. Intermittent fasting is not a new concept, humans have fasted throughout history, weather it’s a typical over night fast, during periods of searching and hunting for food, or for religious reasons. Pilon (2007) defines intermittent fasting as the act of willingly abstaining from some or all food, and in some cases drink, for a pre-determined period of time. The notion of ‘willing’ is the difference between starving and fasting. The intermittent fasting protocol is characterised by the changes between ad libitum feeding and fasting periods (Varady, Bhutani, Church, & Klempel, 2009).


The fasted state according to Coomber (2017) is the point at which the glucose from the meal last eaten is no longer present, and the pancreas senses glucose levels are going to be lower than they should ideally be. Insulin is then suppressed which in turn amplifies glucagon release into the bloodstream and used as energy for day-to-day activity. The glucagon also encourages the breakdown and release of triglycerides, fatty acids, into the blood to be used as energy as well.


What has highlighted intermittent fasting in the media is the research on health benefits related to intermittent fasting.  When intermittent fasting is done properly data has shown it may help extend life, regulate blood glucose, control blood lipids, manage body weight, gain or maintain lean mass.


Although there are many health and weight benefits of intermittent fasting there are some behavioural modifications that need assessing in relation to binge eating following a fasting period (Golbidi et al., 2017).


Comparing popular IF programs

There are many different forms of intermittent fasting with slightly different variations on the fasting and feeding times.  The most popular intermittent fasting programs are alternate day fasting, meal skipping, eat stop eat, leangains, 5:2 diet and the warrior diet.


Alternate day fasting

The alternating day fasting (ADF) recommends you eat every other day, with this intermittent fasting program you would eat on day one within a 12hour window. Then you would fast over night, all-day and then over night again- a 36hour fast. This pattern would continue for as long as the intermittent fasting program is followed. ADF program fasters are recommended to make good eating choices, but are not restricted to certain foods (Berradi, 2011).  A review on alternate day fasting studies (Varady & Hellerstein, 2007)concluded that this type of intermittent fasting on animals was as effective as calorie restrictive diets in decreasing fasting insulin and glucose concentrations. Alternate day fasting was also seen to reduce total plasma cholesterol and triglyceride concentration, and had a beneficial effect on caner risk factors (Mattson, et al, 2016)


Meal skipping

The meal-skipping program was devised from our evolutionary ancestors, with the idea that food was not always readily available. Meal skipping dieters are advised to randomly skip a breakfast or dinner once or twice a week in order to randomly cycle calorie intake. Meal skipping dieters are advised to follow a Paleo based diet, which would remove most if not all processed foods.


Eat stop eat

Eat Stop Eat (Pilon, 2007) recommends taking a 24 hour break from eating once or twice a week and commit to a resistance training based exercise program at least two to three times a week. Eat Stop Eat suggests that fasting twice a week can create a calorie reduction of around 20% in an overall weekly calorie total. Pilon (2007) believes the key to Eat Stop Eat is how flexible and relaxed the guidelines are, which make it easy to follow and be consistent. The bottom line with Pilon’s (2007) Eat Stop Eat is weight loss can be achieved whilst creating a healthier relationship with food and accepting food is a fuel for the body and is to be enjoyed.


Lean gains

Developed by Martin Berkhan (2007) the leangains program is based on a 16hour fast and an 8hour-eating window. Berkhan (2007) says the leangains program is a lifestyle not a diet. It is designed to give followers of this lifestyle more freedom and control of how they eat. Leangains, like east stop eat, recommends training alongside the nutrition aspects. Leangains recommends metabolic resistance training, which uses both weights and bodyweight in a fast paced, circuit-based workout. The idea behind this style of workout is to create an increase in excess post-exercise oxygen consumption (EPOC).


5:2 diet

The 5:2 intermittent fasting diet is characterised by 5 days of eating normally and then 2 fasting days, where calorie intake is restricted to 500kcal/day for women and 600kcal/day for men (Dyson, 2014). The 5:2 diet has no specific restrictions on foods that can be eaten nor does it prescribe a particular exercise regime to follow. The 5:2 diet works on the basis that the two fasting days will decrease the weekly calorie total and by the end of the week put the individual in a calorie deficit for that week.


Warrior diet

Developed by Ori Hofmekler in 2001 the warrior diet was developed t get individuals eating the way they were allegedly designed to eat, according to pre-industrial times. Hofmekler’s warrior diet involves under eating during the day and over eating at night. This is based on ancient warriors who would eat very little during the day and feast after a hunt. Foods recommended on the warrior diet are based on whole foods such as meats, poultry, fish, vegetables and whole grains. The warrior diet prescribes exercising fasted doing high intensity training.


According to the influencers each of these intermittent fasting protocols the fasting is recommended for the long-term health benefits and rapid weigh loss.


Benefits of Intermittent Fasting

There are numerous benefits linked with intermittent fasting, not just weight loss but also hormonal and health benefits.


According to Mark Mattson, senior investigator for the National Institute on Aging, there are protective benefits of fasting on neurons. If you do not eat for 10-16 hours the body will start to go into ketosis and release fatty acids into the blood stream. Research suggests this will protect memory and learning functionality as well as slow any disease process in the brain (Collier, 2013b).


In research (Halberg, et al, 2005) conducted on participants who fasted for 24 hours to see the effects on insulin levels with conclusive evidence fasting drastically reduces insulin levels. Insulin is the hormone secreted after food is consumed or to regulate blood glucose levels (Learney, 2014). It is important to note insulin inhibits lipolysis, which is the breakdown of fats. This in turn results in not being able to mobilise the fats to be used as energy. Having high insulin levels, known as insulin resistant, your blood sugar levels stay higher for longer meaning the glucose being transported around do not make it into the muscle cells and become stored as fat cells(Romaniello & Bornstein, 2013). Increasing insulin sensitivity will mean less insulin is needed to do the same job of the transportation of nutrients into cells in the liver, muscles and stored fat (Romaniello & Bornstein, 2013).


In contrast Clayton, Creese, Skidmore, Stensel and James (2016) conducted a clinical study that showed there is no effect on insulin levels between two control groups but does suggest that a 24 hour severe fast may be used to maintain a calorie deficit by limiting the total amount of calories consumed and therefore may assist in weigh loss.


(Hartman, et al, 1992) suggests short term fasting can increase growth hormone (GH) levels by nearly 6 time more than in a fed state. GH improves the growth of your cells- it helps increase muscle mass, strengthen bones , protects the imune system, helps fight off disease and stay healthy (Romaniello & Bornstein, 2013).


Research suggests eating prevents the release of GH, whilst fasting promotes the release of GH (Pilon, 2007). It has also been suggested in a study from the university of Texas (“Growth hormone affected by starvation,” 2009)that starvation blocks the effects of growth hormone. Although it seems fasting block the action of growth hormone with the fat burning hormone fibroblast growth factor 21 (FGF21). The functions of the FGF21 hormone are to corodinate lipids and glucose metabolism. FGF21 has been seen, in mice, to improve metabolic disorders and could be a candidate for the treatment of obesity (Chen et al., 2017), however this has not been proven in humans.


Another hormone in which fasting has  an effect on is leptin (Romaniello & Bornstein, 2013). Leptin is produced in the fat cells, because of this the more fat tissue an individual has the higher the baseline of leptin. Leptin is known for being the anti starvation hormone, meaning as someone decreases calories leptin levels increase to make an individual start feeling hungry. Fasting counteracts this, seen when loking at the leangains programe, with the use of eating window. Using an eating window will train the individual to eat at a certain time and reduce the risk of overeating because of the low levels of leptin (Romaniello & Bornstein, 2013).


One study (Solianik, Sujeta, Terentjevienė, & Skurvydas, 2016)looking at the effect of a 48hour fast suggests as 48 hour fast will have a positive effect not just on weight loss but also reduces the risks of many chronic diseases such as cancer, neurodegenerative diseases, metabolic syndrome, hypertension, and inflammation.


It has been reported intermittent fasting, alternate day fasting, reduced mammary growth tumours in rats by 65-90% compared with those consuming feed ad libitum (Harvie & Howell, 2016). There are few data on the effects of intermittent fasting on cancer risk, however these studies have not shown a direct comparison between intermittent fasting and cancer in humans.


Research on neurodegenerative diseases suggests it is very difficult to treat but it has been identified that dietary restriction will benefit obese individuals as weight loss will reduce the risk of disease (Mattson, 2003).  It could be concluded that although intermittent fasting has been linked with reducing the risk of neurodegenerative disease it could be the benefit of weight loss due to being on an calorie restrictive diet.


Intermittent Fasting Vs. calories in- calories out

Many researches suggest perhaps it is not the fasting protocol that results in the health benefits but the overall calories reduction created by the protocol (Aksungar, Sarikaya, Coskun, Serteser, & Unsal, 2017; Barnosky, Hoddy, Unterman, & Varady, 2014; Collier, 2013b).


Barnosky (2013) found a superior decrease in body weight by those following a calorie restriction than the intermittent fasting dieters with comparable results in reduction of visceral fat mass, fasting insulin, and insulin resistance.


A 24 month follow up study looking at 23 female subjects aged between 28-42years looked at the comparison of intermittent fasting versus a calorie restricted diet in obese subjects (Aksungar et al., 2017). This single-arm intervention study saw weight loss in both intermittent fasting and calorie restriction as well as a decrease in body mass index (BMI), glucose and insulin whilst seeing an increase in growth hormone and a gradual increase during the calorie restriction period of insulin like growth factor 1 and beginning with the 7thday of the intermittent fasting period. The conclusion of this study suggests a calorie restrictive diet will cause weight loss, however intermittent fasting without a calorie restriction can enhance health and cellular resistance to disease without causing weight loss.


One study (Dyson, 2014)reported there is little evidence to support that the 5:2 intermittent fasting diet was any more effective in weight loss than a conventional weight loss diet, in fact both diets reported to have the same effectiveness in reducing various risk factors for disease.


Coomber (2017) claims weight loss or gain comes down to energy in vs. energy out, known as energy balance, regardless to what diet you follow if the energy in is greater than the energy expenditure then weight gain would be expected.


Energy balance (Bagchi & Sreejayan, 2012)is the balance between calories consumed through eating and drinking and those calories expended through physical activity and metabolic processes. Bagchi and Sreejayan (2012) state overweight and obesity will result from excess calories being eaten and/or inadequate physical activity. Weight loss on the other hand is achieved by reducing the amount of calories eaten, being more physically active or a combination of the two.


An article in the Harvard Health Letter (Komaroff, 2015)suggests although it is simple to burn off the calories you have eaten with physical activity- eat less and move more, recent discoveries make it more complicated than that. Komaroff (2015) states we do not all digest food with the same efficiency with some individuals being able to better than others. Also, not all individuals expend the same energy whilst performing physical activity making the simple calories in vs. calories out argument more difficult to measure.


Intermittent fasting and energy

Anson et al. (2003) studied intermittent fasting on mice, it was seen that mice placed on an intermittent fasting diet than mice fed on ad libitum ate twice as much. It was concluded from this study that the intermittent fasting mice were compensating for the fasting periods by increasing their food intake. It was hypothesised from this that human participating in intermittent fasting would follow the same trend.


A single fasting period of fasting experiment by Sodersten, Bergh and Zandian (2006) reported that skipping dinner in the evening and breakfast the next morning women ate about 20% less and men ate about 30% more after fasting.  Longer testing would need to be able to verify this report.


When looking at intermittent fasting and energy expenditure Soeters er al. (2009) suggests intermittent fasting significantly lowers individuals resting energy expenditure after two weeks compared to those following a standard diet. More research into this field is needed to be able to conclude any definitive answers.



Intermittent fasting, in simple terms, is making a conscious decision to skip certain meals or spend a certain amount of time without eating (Coomber, 2017). When intermittent fasting is followed properly it has been suggested there are many health and hormonal benefits that can be achieved though the fasting process. However, these benefits, such as reduced risk of cardiovascular disease, diabetes, hypertension and cancer can also be seen in studies looking simply at weight loss and could be concluded these health benefits are because of the weight loss and not just the intermittent fasting.


Some research however has shown intermittent fasting could have a beneficial effect on insulin response (Halberg, et al, 2005), growth hormone (Pilon, 2007), and leptin (Romaniello & Bornstein, 2013). All of these benefits have also been linked with weight loss, such as insulin, growth hormone and leptin (Romaniello & Bornstein, 2013)due to the hormonal effects they have on the body and weight loss.


The popular intermittent fasting protocols looked at within this assignment are all based loosely on the energy balance equation- calories in vs. calories out. The protocols either specify certain ways of eating within the feeding part of the diet or encourage physical activity alongside the diet.


Pilon (2007) raised the question – ‘have we been led to overlook the simplest form of reducing calories and loosing weight’- short periods of fasting. Pilon (2007) goes on to state, prolonged calorie restriction is the only proven nutritional method of weight loss. If the diet plan allows you to stay in a calorie deficit for a long period of time, then you have a very good chance of achieving weight loss success.


A review (Franklin, 2013)agrees with Pilon stating it has long been reported that energy restriction can increase longevity and promote weight loss, what is less well known and unable to determine are benefits of  intermittent fasting to do with the fasting or to do with the calorie restriction.


Schwenk (2014) also believes the matter of calories consumed versus calories being expended- although somewhat simplistic nutritionally, is still relevant no matter what diet an individual follows. Choosing a weigh loss plan should be based on individual preferences and likelihood of adherence.


Whether an individual follows the 5:2 diet, warrior diet or any of the other intermittent fasting protocols it is down to the adherence of the dieter to whether it works or not. Also, calorie balance must be looked at, as if the individual follows the diet ‘rules’ to there strictest form but continually overeats research suggests weight loss will not occur and possibly weight gain may happen depending on the severity of the calorie surplus.


In conclusion, it would seem intermittent fasting-although more research is needed, does work as a dietary approach to weight loss and a strategy for weight management. Although the majority of the larger studies are conducted on mice some smaller studies have been reported on humans to provide evidence to the health clams made by intermittent fasting advocates.


Intermittent fasting as many other popular diets do follow a energy balance approach to elicit weight loss but like most diets intermittent fasting needs to be followed properly and adhered to in order to achieve weight loss.


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