Intermittent Fasting: Benefits, Methods & Risks

2 What is intermittent fasting

The benefits of intermittent fasting have undergone vast research since its popularity boomed within the last decade, but is it just another diet fad?

In today’s world, the sheer amount of dieting and weight loss techniques and methods can be intimidating and more than a little bit baffling. From plant based diets, ketogenic diets, Weight Watchers, Slimming World to name but a few…the options are seemingly endless.

Intermittent fasting is a diet plan that switches between fasting and eating on a regular schedule. Where most diets focus on what you can eat, intermittent fasting focuses on when you can. Research shows that intermittent fasting is a way to both manage your weight and prevent — or even reverse — some diseases. 

But what is intermittent fasting? And is it safe? 

In this article, we will be exploring the ins and outs of this popular diet plan, laying out the intermittent fasting benefits and side effects, as well as all the answers you need on how to execute it responsibly and effectively.


  1. What is Intermittent Fasting?
  2. The Types of Intermittent Fasting
  3. What are the Benefits of Intermittent Fasting
  4. How Does Intermittent Fasting Compare against other Dieting Methods?
  5. Tips for Intermittent Fasting
  6. Intermittent Fasting Risks

Before we jump in, if you would like to expand your knowledge on nutrition and how it affects the body, take a look at our Level 4 Advanced Sports Nutrition Course.

Alternatively, you can download our latest course prospectus which provides you with all you need to know about all the courses we offer here at OriGym.

What is Intermittent Fasting?

2 What is intermittent fasting

Intermittent fasting has become incredibly popular in recent years, and with good reason: it provides a highly structured approach to weight loss. It is easy-to-follow (and therefore easy to stay motivated whilst following it), and better yet it does not require the addition of exercise. 

Intermittent fasting is an effective method, but it does take some will power and determination, as well good organisation and careful planning ahead. 

But how does it work? The name gives a hint: you switch between cycles of eating normally, and calorie restriction. The days when you restrict your calories constitute the fasting element of the diet, and that’s about it for the basic premise! 

Naturally, it’s not that simple and there are a range of particular ways to manage which days you fast, how long you fast for, and how many calories per week you consume. But don’t worry about that for now, we’ll break it all down for you later on in this article. 

The key to intermittent fasting isn’t controlling what you eat like with other weight loss methods, but rather when you eat it. For example, you might fast for two days a week, then eat normally for the rest of the week, or you may restrict your eating hours to a certain time window every day. 

The benefits of intermittent fasting come from its ease. It is considered a bit of a “life hack”, or a simple way to lose weight, as you’re not having to constantly think of low-calorie meals, or different exercises to complete.

While it is not featured in our How To Get A Summer Body article, we would consider fasting among the most effective ways to slim down your waist!

At a basic level, intermittent fasting is just limiting the amount of food you eat, and thus reducing the number of calories you consume. Easy, right? 

Different Types of Intermittent Fasting

This is where it starts to get a little bit more complex, as there are actually lots of different methods and formulas for intermittent fasting. 

Don’t panic, though! Try not to think of this as an information overload. Instead, see it as a handy way of finding the type of intermittent fasting that suits you best.  

As we mentioned earlier, weight loss is highly individual, and intermittent fasting is no different. It’s vital to find a method that works with your lifestyle. Luckily, there are plenty of types of intermittent fasting, so you’re bound to find a suitable one! 

The Twice-Week Method, or 5:2 Method

6 benefits of intermittent fasting bodybuilding

The 5:2 method, also known as the Fast Diet, focuses on fasting twice per week, while eating as normal for the remaining five days. 

Popularised by British journalist Michael Mosley, the method is fairly straightforward; on the days you are fasting, your calorie intake should be restricted to 500–600 per day (with men recommended to eat 600 calories and women suggested 500)

The days the fasts fall on are completely up to the individual, and there is no structure that offers an increased effectiveness.  

It is highly recommended for this method of intermittent fasting that you have your daily 500-600 calories in two sittings, usually in two small meals to keep you going throughout the day. 

The 16:8 Method

benefits of intermittent fasting

One of the most popular forms of intermittent fasting, the 16:8 method focuses on breaking up the 24-hour day into time frames of fasting and eating, rather than the entire week. 

Acknowledged as one of the easiest forms of intermittent fasting, it’s all about limiting the consumption of foods and high-calorie drinks to an eight-hour eating window during the day.

For example, with the day starting at midnight you might fast until 12pm. You would then have the eight-hour period, until 8pm, in order to eat. After 8pm, you would fast again.

Similarly to the 5:2 diet plan, the designated times that you select for your eating window are completely your choice. This cycle can be repeated as frequently as you like, from doing it just one or two days per week to maintaining it all week long, depending on your personal preference.

One of the intermittent fasting benefits that is linked directly to the 16:8 method is its effectiveness in controlling blood sugar levels. 

24 Hour Fasting

intermittent fasting benefits

This method of fasting requires a slightly higher demand of commitment than the two we have looked at so far. 

It’s a very simple method of fasting which requires you to not eat for a 24 hour period, as the name suggests. The most popular windows that participants seem to opt for are from breakfast to breakfast, or lunch to lunch the following day, and many opt to do this between once and twice a week.

Once again, 24 hour fasting can be incorporated into your week as and when best suits your lifestyle and structure. Of course, you are encouraged to return to a regular, healthy diet and meal structure on the days when you eat. 

Those who opt for the 24 hour fast plan are permitted to consume water, tea, and other low-calorie drinks during the fasting period. You can also consume multiple options available in OriGym's shortlist of the best keto drinks - so be sure to check that out so you don't have to restrict yourself solely to water!

If you're familiar with the yoga diet, then you may well have already partaken in this sort of one day fast. If not and you would like to find out more, we have an entire guide on what is a yoga diet? With everything you need to know to execute it safely.

A common side note for the 24 hour fast is it may provoke fatigue, headaches and irritability, however it has been recorded that with consistent practice of this method, those side effects can decrease.

Alternate Day Fasting

7 benefits of intermittent fasting bodybuilding

Alternate day fasting, often abbreviated to ADF, is a very structured method of intermittent fasting. The basic idea is that you fast on one day and then eat what you want the next. This way you only need to restrict what you eat half of the time. 

On your fasting days, you are still allowed to eat around 500 calories and drink as many low-calorie drinks as you wish

Whilst this isn’t quite as flexible as some of the other methods we’ve looked at, it’s really effective and requires minimal effort to plan and schedule. 

However, this relatively more intense form of intermittent fasting is not recommended for those who are new to this style of dieting and it is worth mentioning that it may be a more difficult style of fasting to maintain long term. 

Alternate day fasting might be a better technique to consider once your body has adapted to the demands of intermittent fasting, having eased yourself in with another, less rigorous method. 

The Warrior Diet

4 Intermittent fasting tips

The Warrior Diet certainly sounds rigorous, but you can declare war on excess weight with this form of intermittent fasting! 

This method was formulated by a former Special Forces soldier and based on the eating patterns of ancient warriors, who consumed little during the day and then feasted at night - so you can expect it to be slightly more challenging than the other forms of intermittent fasting.

For the Warrior Diet, it requires you to undereat for 20 hours of the day and then consume as much food as you desire at night. During the 20 hour fasting period, dieters are allowed to consume small amounts of dairy products, as well as raw fruits and vegetables, hard-boiled eggs and as many low-calorie drinks as they wish.

After 20 hours, you can essentially eat as much of any food you like within the remaining four hour window. 

This method is said to burn fat effectively, as well as potentially increase concentration thanks to it’s highly rigorous and focused approach. 

 It is important to note that the Warrior Diet is quite an extreme form of intermittent fasting, however, and like alternate day fasting is perhaps best attempted by more experienced fasters. 

What are The Benefits of Intermittent Fasting?

So, what exactly are the benefits of intermittent fasting? As you can probably imagine, intermittent fasting works in a way that limits the amount of food you are consuming, which in turn limits how many calories and fats your body is taking in. 

While it is a great tool for weight loss, the health benefits of intermittent fasting go far beyond that; from improving your skin, to cardiovascular health - let us explore some of them in more depth. 

#1 Improves Cell Function

8 benefits of intermittent fasting weight loss

Perhaps one of the most overlooked or simply misunderstood benefits of intermittent fasting is the role it can play in the function of the cells. 

The cells are responsible for a multitude of bodily functions, the six primary functions being: energy production, structure and support, facilitating growth through mitosis, assisting in reproduction, allowing passive and active transport and creating metabolic reactions. 

When we fast, it increases autophagy which is a natural mechanism of the cells. It is important for cleaning out unnecessary and damaged cells, and therefore the longer we engage in a fast, the longer our body has time to heal and rid itself of any present junk

A small-scale 2019 study published in Nutrients found that time-restricted eating, which in this case fell between 8am and 2pm, increased the expression of the autophagy gene LC3A and the protein MTOR. This therefore confirmed that intermittent fasting can improve the function of cells.

Furthermore, another study published in Autophagy which further supported the theory that intermittent fasting increases autophagy, suggested that by increasing the natural mechanism it could offer protective benefits for the brain.

In addition to its ability to assist with cleaning out bad cells, another notable cell function which is said to be assisted through the practise of fasting is weight loss. 

You may be interested to know that glutamine plays an essential role in promoting and maintaining the function of various organs and cells, so supplementing with L-Glutamine can also positively impact the cells. You can read more about the benefits of L-Glutamine here.

It is suggested that this should be done by lowering blood levels of insulin, as well as increasing the human growth hormone, both of which play a vital role in facilitating fat burning - this, we will discuss further on. 

#2 Reduces Oxidative Stress and Inflammation

health benefits of intermittent fasting

Intermittent fasting, particularly in its alternate day form, has been suggested through research to reduce oxidative stress markers and keep control of inflammation in overweight adults. 

While oxidation is a completely normal and necessary process that takes place in your body, oxidative stress occurs when there’s an imbalance between free radical activity and antioxidant activity in the human body - this can result in inflammation.

When functioning properly, free radicals can help fight off pathogens (which lead to infections), however, when there is an imbalance and oxidative stress is present, this can create a number of issues including many ageing and chronic conditions.

A number of present studies indicate that intermittent fasting may enhance the body’s resistance to oxidative stress, in turn, preventing the risk of such chronic conditions.

For instance, a 2019 study into how dietary intake regulates the circulating inflammatory monocyte pool concluded that fasting can ease and improve symptoms of inflammation. It does this by reducing the levels of monocytes in the blood, which are the cells that cause inflammation. Therefore, by reducing those, you’re in turn preventing the risk of inflammation.

Additionally, there are multiple supplements available that offer anti-inflammatory properties, for instance, it is among the most lauded benefits of the cod liver oil tablets!

#3 Reduces Risk of Cardiovascular Issues

10 health benefits of intermittent fasting

The heart is a particularly vulnerable part of the body, especially when it comes to our eating habits; all those high-fat and high-sodium meals are particularly bad news. However, intermittent fasting can help as there is a growing consensus that regulating when you eat, along with how often, can have real benefits for your heart’s health. 

There are a number of various health markers (also referred to as “risk factors”) that are commonly associated with heart disease. By monitoring these factors we can decrease the risk of developing heart disease as a whole - and that is where intermittent fasting comes in.

With strengthening the function of your cardiovascular/circulatory system, it causes a snowball effect of benefits on the body. You can read more about this in the 11 components of fitness article.

Conclusive research suggests that intermittent fasting can improve many of these risk factors, including: inflammatory markers, blood pressure, cholesterol (both total and LDL), blood triglycerides and blood sugar levels.

Additionally, following on from the previous benefit, intermittent fasting presents great advantages for cardiovascular health by reducing oxidative stress. 

This form of stress damages tissue within the body, including the cardiac muscle tissue present in your heart, which as a consequence can lead to chronic heart conditions. By reducing the risk of this stress, this in exchange reduces the risk of cardiovascular issues. 

#4 Encourages Weight Loss

benefits of intermittent fasting weight loss

Perhaps one of the headline health benefits of intermittent fasting, and a big reason that many people turn to this technique, is the intermittent fasting benefits for weight loss.  

This all boils down to a simple explanation: to lose weight, you want to be in a calorie deficit (consume fewer calories than your body expends). By restricting the time in which you consume food you should, in theory, restrict the amount of food that you eat on a daily basis.

When you reduce calorie intake and throw in the increased cell function we talked about earlier, then you’re sure to burn some excess fat, which then leads to weight loss. This is one of the most established proven benefits of intermittent fasting, and a big reason why it’s increasingly popular!

According to a 2015 article published in the Journal of the Academy of Nutrition and Dietetics, the research suggests that intermittent fasting in any form can play a significant factor in weight loss. The data shows that the average weight loss from results across 13 studies ranged from 1.3% for a two-week trial, to 8% for an eight-week trial. 

Additionally, intermittent fasting’s role in enhancing hormone function can play a part in weight loss. Studies suggest that this form of dieting can lower insulin levels, increase human growth hormone levels and increase the amount of noradrenaline in the body - all of which increase the breakdown of body fat and utilise it for energy. 

As a result of this, science indicates that intermittent fasting can increase the body’s metabolic rate by 3.6-14%, resulting in more calories being burnt.

All things considered, intermittent fasting can be an incredibly powerful weight loss tool. Just be vigilant when it comes to what you’re putting in your body to avoid the risk of overeating during your eating window. 

#5 Improves Skin

11 intermittent fasting benefits

It is no secret that what we eat can affect the condition of our skin, and the science behind intermittent fasting plays into that.

This comes as a snowball effect from other intermittent fasting health benefits mentioned within this article. For instance, intermittent fasting restricts your calories and the beneficial side effect of this is that reduced calories means increased stem cells. Stem cells provide the skin with collagen and elastin properties, which directly results in restoring healthier looking skin.

While fasting offers its own skin benefits, what about if you could cobine this with another effective supplement that contains the same properties that you can have during your fasting window? Green tea is your answer. Not only is it fast friendly, but green tea benefits the skin in a multitude of ways.

We’ve talked about how intermittent fasting can reduce inflammation which, in addition to reducing the risks of chronic diseases, also presents great benefits for your skin as inflammation is the cause of skin traumas such as acne. It works in a similar way by reducing blood sugar levels, too, which can also increase acne when high.

Based on the common factors that cause acne, such as: inflammation, high levels of insulin, and lack of restorative sleep, and the proven advantages intermittent fasting presents for each of these, this type of dieting could improve skin issues in theory.  

#6 Enhances Bodybuilding Performance

intermittent fasting health benefits

The intermittent fasting benefits for bodybuilding can apply to both training bodybuilders or casual gym-goers who are looking to get into shape, though it is worth noting that it may not apply as much to those competing, as that usually entails regular eating periods every 2-4 hours.

The benefits of intermittent fasting for bodybuilding come off the back of the more physical benefits in this list. For example, through its proven advantages in decreasing cholesterol, increasing the human growth hormone, reducing inflammation and increasing fat loss, these all play a major role in athletic and bodybuilding performance, therefore it has an indirect knock on effect in positively impacting bodybuilders.

Additionally, as one of the primary benefits of intermittent fasting is fat loss, which it achieves through reduced calorie intake, this provides a major advantage in the bodybuilding industry, particularly in those competing. 

Fat loss is what will allow bodybuilding competitors to achieve the defined, vascular physique needed in competitions. 

You may also want to check out the benefits of beta-alanine, as they're a highly praised supplement within the bodybuilding industry.

While the verdict is still out on the intermittent fasting health benefits for bodybuilders, it holds a great reputation amongst the community regardless of the little scientific evidence.

#7 Lowers Risk of Type 2 Diabetes

12 benefits of intermittent fasting

Some diabetes charities and organisations suggest that intermittent fasting, specifically the 5:2 method, is effective in managing type 2 diabetes. Whilst intermittent fasting certainly is not a cure for diabetes and should always be approached with relative caution, there are some promising studies for this method to help manage the condition.

Intermittent fasting is said to stabilise blood sugar levels in those with diabetes as it resets insulin in the body. 

Research suggests it does this by restricting calorie intake and limiting eating periods into windows, which improves insulin resistance (a marker of type 2 diabetes) by encouraging the insulin levels to fall and in turn lead to an impressive reduction in blood sugar levels. Higher blood sugars are of course a major cause for concern in those diagnosed or at risk of diabetes.

Data of multiple research studies into the correlation between fasting and type 2 diabetes markers found that during intermittent fasting, subjects noticed that their fasting blood sugar reduced by 3-6%, while fasting insulin levels reduced by 20-31%. 

Furthermore, another study which used a group of rats for subjects suggested that intermittent fasting could have protected against kidney damage, which is one of the most severe complications of diabetes.

To put it simply, anything that causes reduced insulin resistance should, in theory, help lower blood sugar levels and therefore protect against type 2 diabetes - further expanding the list of intermittent fasting health benefits.

#8 Improves Brain Function

13 benefits of intermittent fasting

The health benefits of intermittent fasting are not simply limited to your physical health; it is believed that this form of dieting can improve brain function, too. 

An increased brain function presents advantages in a vast number of areas, such as your memory, cognitive skills, as well as concentration and self control.  It is said to impact brain function through its role in increasing the growth of nerve cells, as well as increasing the levels of the brain hormone, brain-derived neurotrophic factor (BDNF), which is a deficiency of which has been implicated in depression and various other brain problems.

A 2018 study found that intermittent fasting could help protect against the decline in memory that comes naturally with age, explaining that the form of dieting improves connections in the brain’s hippocampus and also protects against amyloid plaques, which are found in patients with Alzheimer’s. 

While more research is needed to confirm these findings for certain, it is fair to say, what is good for the body is often good for the brain, too. You may also find brain function can be improved through the usage of vitamins. Our guide on the best vitamins for energy provides more details.

#9 Prolongs Your Lifespan

intermittent fasting health benefits

Intermittent fasting has gained a great following from the anti-ageing community for its vast benefits, one of which is a suggested longer lifespan.

This likely comes as a result of intermittent fasting’s role in creating resistance to a number of age-related diseases. 

In one study which allowed one group of rats unlimited food around the clock, and another fed during intervals, the results found that the group that fasted every other day lived 83% longer than the rats who had freedom with their eating times.

Given the known benefits of intermittent fasting for metabolism and other notable health markers, it makes sense that by restricting our eating times and following a structured eating routine, this could in turn result in an elongated and healthier life. 

This particular health benefit comes with a slight caveat: to date, the benefits of intermittent fasting for lifespan have only been studied using rats as subjects and human studies have struggled to replicate the results, therefore more research is needed to be confident.

#10 May Prevent Cancer

health benefits of intermittent fasting

In science and health research, intermittent fasting has been primarily studied for control of diabetes, however, more recent studies have begun looking into its potential as an approach to cancer prevention or treatment.

Intermittent fasting, particularly in its alternate-day form, may reduce the risk of cancer risk by decreasing the development of lymphoma (a type of cancer that begins in infection-fighting cells of the immune system), as well as limiting tumor survival and slowing the spread of cancer cells, according to a review of studies published in The American Journal of Clinical Nutrition. 

The research behind this benefit of intermittent fasting suggests that it is effective in reducing the occurrence of spontaneous tumors and suppressing the growth of many types of induced tumors while increasing their sensitivity to chemotherapy and irradiation.

This also suggests that fasting could offer benefits for cancer patients by reducing various side effects of chemotherapy. Adttionally, there are a number of foods that contain cancer reduction properties, many of which you can find within our shortlist of the best super fruits to add to your diet today.

Furthermore, fasting has been shown to offer several positive effects on metabolism that may lead to reduced risk of cancer. It is suggested that fasting inhibits the growth of the energy metabolism found in cancer cells, and again, making them more susceptible to treatment.

Though human studies are necessary to confirm this, there is promising evidence from animal studies indicating that intermittent fasting may help prevent cancer.

How Does Intermittent Fasting Compare against other Dieting Methods?

14 intermittent fasting benefits

When looking into diets and weight loss techniques, it is worth noting that our bodies are all different; whilst a ketogenic diet might work wonders for one person, it may offer little to no results for another.

The human body and its metabolic systems are all so individual, there is no definitive “best” way to diet, however, let’s compare intermittent fasting to some other weight loss techniques so you can see how it differs.

The majority of popular diets focus on what you are eating in contrast with the intermittent fasting method, which simply controls when you are eating. For example, the ketogenic diet dramatically reduces your carbohydrate intake, similar to the Atkins diet, and increases your fat intake instead.

A Mediterranean diet focuses on specific food types, like fish, vegetables and whole grains, whilst reducing red meat and eliminating sugar from your diet. 

This is a key point of difference to intermittent fasting. Outside of the periods in which you are fasting, you are free to eat as you normally would. There is no need to cut out carbohydrates, or only eat fish and vegetables, or even keep track of your macronutrients. 

For many, this offers one of the biggest advantages of this form of dieting, as it allows you to maintain a non-restricted lifestyle during the periods that you’re not fasting. 

All these weight loss methods will, if followed correctly, reduce calorie intake and result in weight loss. However, not all of these methods are as flexible as intermittent fasting. They need to be followed strictly every day for you to see results. 

In contrast, intermittent fasting allows you to pick and choose when you do it, arranging your fasting periods to days that suit you. Intermittent fasting also doesn’t require extensive research and meal planning in order to stick to a dietary plan or regime. 

For alternative diet plans, we think you may find the following articles an interesting read:

Tips for Intermittent Fasting

15 intermittent fasting benefits

So, now you have decided you’re interested in intermittent fasting, where do you begin?

We’ve already explained the different types of fasting, so make sure to read each one carefully to discover a method which will suit you and your lifestyle the best. From there, we have provided you with some handy tips to help ease you in and make a smooth transition to the fasting lifestyle!

Drink plenty of water

Thirst can often be mistaken for hunger, especially when we are fasting. Regularly drinking water throughout your fast won’t break any of the rules and will keep you feeling fuller. 

When we eat, we’re often hydrating our bodies without our knowledge, as many foods are water-dense; however this, of course, is not possible during fasting periods. A general rule of thumb is for women to drink 2.2 litres of water a day, and men 3 litres. This applies to both everyday life, but particularly when you fast. 

Hydration is key to maintaining your health, as it can prevent the occurrence of any side effects that can happen as a result of fasting. 

Start simple, and try things out

One of the primary and most recommended tips for intermittent fasting is to approach it slowly. When you first start fasting, try and ease yourself in: don’t go straight in for a 24 hour fast as the likelihood is you won’t maintain this. 

It is worth trying out a few different methods for a short period of time to identify which one best suits you and your lifestyle. This will enable you to find the technique that fits into you day-to-day life, making it easier to sustain and adapt into a lifestyle as opposed to a forced diet.

Stay Busy

It is advised to keep yourself busy during your fasting periods as this will occupy your mind and divert your attention away from any feelings of hunger. 

We often find that eating can become a habit, as opposed to a necessity in our lives - this is especially the case with snacking. Like with anything, breaking a habit is not an easy task, that is why it is important to occupy yourself with other things.

Focus on things ideally away from your kitchen, whether it is work or a hobby you enjoy, that way you’ll find the fasting hours pass. 

Avoid overeating outside of fasting

This is a key one for beginners. Initially, when you stop your fast period, the temptation will be to eat an enormous, probably unhealthy meal. Not only will this possibly undo your hard work, but it will make it harder to fast next time. 

Eat slowly and steadily and try to avoid filling up on carbohydrates. This will all make it much easier when you next fast!

Pay attention

While this may seem minimal, paying attention is perhaps among the most important tips for intermittent fasting. When fasting, you’ve got to be in tune with your body and listen to what it is telling you. 

At the beginning of your intermittent fasting program, you may experience feelings of weakness and hunger. However, if you start to feel extremely dizzy or very cold, have something to eat. This is usually a sign that your body needs to eat, rather than wants to eat: we recommend breaking your fast in this scenario and listening to it.

Intermittent Fasting: Risks and Side Effects

16 benefits of intermittent fasting

Very few weight loss methods are risk free; drastically changing your eating habits will always have effects, and while most of them are positive, it’s worth keeping an eye out for any negative ones. 

  • Increased Hunger/Risk of Overeating - It may come as no surprise that you might encounter stomach rumbling during fasting periods, especially if you’re used to constant grazing. If this is not managed correctly, it could lead to overeating, resulting in a calorie surplus and in fact having the opposite effect than desired.
  • Risk of Dehydration - Often considered a risk as when people don’t eat, then can also forget to drink. This can be simply cobatted by paying special attention to hydrating your body during fasting periods.
  • Could Cause Headaches - Headaches are a common side effect to new fasters and often disappear following the first few fasts. If you need help in combating this, taking extra salt is advised as it can help mitigate headaches. 
  • Increased Fatigue - Another symptom many people new to intermittent fasting experience is a sense of grogginess. This happens as your body is running on less energy than it usually would, and since this form of dieting can increase stress levels, it may also have a negative effect on sleep patterns initially.
  • Increased Irritability - For many newbies to fasting, the body will go through a sensation of sugar withdrawal during fasting, leading to heightened irritability. However, over time your body will adapt and regulate to its new pattern. 
  • Could Cause Constipation -  A very common side effect of intermittent fasting is constipation. The reason for this is simple: less going in means less going out. However, this is a normal response to eating less. 
  • Decreased Tolerance to Alcohol - This one is simple, we have probably all experienced that you get drunk faster on an empty stomach. It is also important to note that alcohol does contain calories, so if consumed outside your eating window will break your fast.

intermittent fasting for weight loss

Additionally, there are a number of groups that we would advise to refrain from this form of dieting. You should not do intermittent fasting if you are:

  • Underweight (BMI < 18.5) or have an eating disorder 
  • Pregnant women  – as your body requires extra nutrients for the fetus
  • Women breastfeeding – for the same reason as the above; your body needs extra nutrients for the child
  • Under 18 – In order to grow efficiently, your body needs the additional nutrients

With the following groups, while you are not advised against fasting completely, it is recommended that you seek medical supervision: 

  • Those with diabetes mellitus type 1 or type 2.
  • Those who take prescription medication
  • Anyone with gout or high uric acid.
  • Anyone with serious medical conditions, such as: heart, liver or kidney disease

Dieting and weight loss should never come at a cost to your health. In terms of side effects, many of these are rare but still present dangers: if you exercise caution and vigilance, as well as remain hydrated, you should avoid them. 


As you can see, there are many forms of intermittent fasting. If you are taking your first steps into this method of weight loss, then how about trying a few styles to see which one you find the most effective and manageable. Maybe give a handful of styles a week’s trial: this will help you work out which one feels the most effective, and balances weight loss with practical considerations. 

 If you were previously wondering ‘does intermittent fasting work?’’, we hope this article on the health benefits of intermittent fasting has provided you with confidence in its effectiveness, along with all the relevant information to approach a fast safely.

If you have enjoyed learning about intermittent fasting, then you may be interested in developing your nutrition knowledge as a whole. Here at OriGym, we offer UK leading personal training and nutrition courses which will enable you to branch out into a successful career in the fitness industry.

Head over to our personal trainer courses page for more information, or download our course prospectus here. 


  1. R. E. Patterson and D. D. Sears (2017) Metabolic Effects of Intermittent Fasting, Annual Review of Nutrition, vol 37
  2. R de Cabo, and M P. Mattson, (2019) Effects of Intermittent Fasting on Health, Aging, and Disease, The New England Journal of Medicine, vol 381
  3. R Antoni ,K Johnston , A Collins , & M Robertson, (2017). Effects of intermittent fasting on glucose and lipid metabolism. Proceedings of the Nutrition Society, 76(3),
  4. M Harvie,A Howell,  (2017). "Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects—A Narrative Review of Human and Animal Evidence" Behav. Sci. 7, (1)
  5. Shin BK, Kang S, Kim DS, Park S. Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer's disease-induced estrogen deficient rats. Exp Biol Med (Maywood). 2018 Feb;243(4):334-343. doi: 10.1177/1535370217751610. Epub 2018 Jan 7. PMID: 29307281; PMCID: PMC6022926.

Written by Annie Williams

Fitness Content Executive, OriGym

Join Annie on Facebook at the OriGym Facebook Group

Graduating from Liverpool John Moores University with a BA (Hons) in Journalism, Annie specialises in mental and physical wellbeing, with a specific interest in nutrition and mindfulness. Her long standing interest in fitness is what brought her to OriGym, and led her to become a qualified Personal Trainer and obtain specialist qualifications in Advanced Sports Nutrition. Annie’s primary professional attraction lies in following and tracking the ever-changing trends in the fitness industry. Beyond OriGym, Annie divides her time between personal writing, her passion for the countryside and mountain walking, and charitable runs.

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