Intermittent fasting is the use of controlled periods of eating and fasting (ie: not eating) to improve one’s health, and is one of 2020s biggest health and fitness trends.
This guide will help you understand what intermittent fasting is, if it’s right for you, and will give you all the tools you need to get started with this brilliant dietary hack.
Although intermittent fasting has been practiced for millenia by cultures around the world; wider interest in the potentially powerful health benefits of this dietary practice has only recently exploded, with a growing body of research suggesting intermittent fasting could be a great addition to your lifestyle.
This cyclical way of eating is being used by people to improve their health, lose weight more consistently and make dieting and changing the way they eat much, much more straightforward.
What is Intermittent Fasting?
Intermittent fasting is the use of a deliberate eating schedule which alternates between periods of feast (eating) and fast (not eating)
This cyclical eating pattern is perfectly natural and safe, and has been the default for humanity for much of our existence on earth. We live in a time when your next meal is only a walk to the refrigerator away, but this hasn’t always been the case.
Our ancestors often fasted for extended periods whilst searching for their next meal, and our bodies have evolved to respond effectively to this situation in ways which we are only just beginning to understand, and which hold many potential benefits for us.
Unlike most approaches to dieting, this isn’t so much about what you eat, as it is about when you eat (although what you eat is still important! We recommend following a ketogenic diet here at I Eat Keto – which you can read more about here)
Intermittent fasting is all about controlling the periods during which you eat, generally by condensing your eating window into a smaller part of your day than you usually would.
A common method of intermittent fasting is the 16/8 method, shrinking the window during which you eat down to 8 hours of the day, followed by a 16 hour fast until your next meal.
This element of controlling when you eat is one of the key benefits of fasting. For many of us eating is a habit, and often a bad habit at that, with plenty of snacking and the mistaking of hunger for other emotions.
Following an intermittent fasting protocol seeks to reset these bad eating habits, by giving a very simple set of rules to follow.
By consciously choosing not to eat for specified periods of the day or week, we build up discipline and a changed relationship with our habits and emotions surrounding food, alongside gaining other health benefits which will be described later.
It’s important to note that fasting is not about starving yourself. Starvation is suffering and potential bodily harm caused by the extended absence of food.
Fasting on the other hand is a controlled restriction of eating for a limited period of time, intended to produce beneficial changes in the body.
However due to fasting being about restricting food intake, it’s important to note now before going any further that this should not be tried by people who are underweight or suffer from eating disorders such as anorexia.
In trying fasting for yourself, listen to your body, and don’t push yourself to fast for too long too quickly should you experience side effects.
Fasting is something that will become easier with repetition so start out small and progress to longer fasts rather than jumping in at the deep end.
Health Benefits of Fasting
Let’s dive into why intermittent fasting is great lifestyle addition, by looking at some research backed health benefits.
Research into fasting is a growing field, with interest exploding in the past couple of years. At present much of the research is in early stages or conducted on small scale groups or animals but there have been a couple of large scale studies showing promise with more to come.
So here are some of the main benefits of intermittent fasting:
- BETTER WEIGHT LOSS: We’ll go into this area in a lot more details in a moment, but suffice to say intermittent fasting can help to lose fat and in particular belly fat. Most interesting is that it is able to help you lose visceral fat, without as high a loss of lean body mass (which you want to keep) as compared to a constant calorie restricted diet. (1) (2) (3)
- IMPROVED INSULIN SENSITIVITY: Intermittent fasting has been demonstrated to improve insulin sensitivity and reduce resistance, with one study showing a reduction in fasting insulin levels of 20-30%, and a reduction in blood sugar by 3-6%, both of which are key factors in diabetes. (4) (5)
- IMPROVED HEART HEALTH: Fasting has been demonstrated to improve many of the health markers related to heart conditions. Blood triglycerides, LDL cholesterol, blood sugar, insulin and inflammatory markers have all been seen to have improved in experiments involving fasting. (6) (7)
- REDUCED LEVELS OF INFLAMMATION: A number of studies have demonstrated a reduction in the key markers of inflammation, which is considered one of the key components in many long term chronic diseases, with one study describing ‘striking reductions in markers of oxidative stress’. (8) (9)
- IMPROVED BRAIN HEALTH: Intermittent fasting has shown some potential to aid brain health, increasing production of the brain hormone BDNF and assisting the growth of new nerve cells and connections. There is also some evidence in animal studies of the potential to protect against Alzheimer’s disease, although more work is needed with human trials. (10) (11) (12) (13) (14)
- CANCER: Disclaimer here: these are currently in animal studies so take these with a pinch of salt. Some studies have shown a preventative effect of intermittent fasting on cancer development in animal studies, as well as improving the effect of chemotherapy in specific cases. (15) (16) (17)
- IMPROVED MENTAL CLARITY AND FOCUS: Intermittent fasting can impact brain chemistry as mentioned, with improvements to focus and concentration as well as showing the potential to improve mood and depression. (18) (19)
- INCREASED LEVELS OF GROWTH HORMONE: One of the key hormonal ingredients in fat burning and muscle growth, HGH (Human Growth Hormone) is shown to significantly increase during fasting. This change in body chemistry can prime you for muscle gain and improved fat burning. (20)
- INCREASED AUTOPHAGY AND CELL CLEANSING: This discovery was awarded the Nobel Prize in medicine in 2016. Fasting can activate and increase the process of ‘autophagy’ – your body’s way of spring-cleaning itself, removing dead and unhealthy cells throughout the body. (21) (22)
- POTENTIALLY INCREASED LIFESPAN AND ANTI-AGING: This is an exciting potential benefit of integrating fasting into your lifestyle over the long term. Multiple animal studies have shown the potential for increased lifespans with regular fasting. Some initial studies into human populations that regularly fast are also showing promise with some caveats. (23) (24) (25)
Bear in mind that many of these studies are in early stages or are animal models, but with growing interest comes greater funding and hopefully higher quality human studies to come.
The Biggest Benefit of Fasting? Simplicity
So there are plenty of health related benefits to fasting as discussed. But really the biggest advantage of all from intermittent fasting has to be the simplicity of the approach.
Many diets have potent weight loss potential (such as the keto diet, done right) but the biggest pitfall is adherence. Many diets are restrictive and awkward to fit into your lifestyle, making the likelihood of ‘falling off the wagon’ so much higher.
At the end of the day, the best diet for you is the one you can maintain.
That’s where fasting can be so great. You don’t need special ingredients, you don’t need to avoid any specific foods. You don’t need to spend all your time meal prepping, in fact, you’ll likely spend less time dealing with food than usual, as you’ll be skipping certain meals.
Fasting is simplifying your diet rather than complicating it, and that’s the biggest benefit of all.
Fasting For Weight Loss
The reason you’re most likely here is to find out can intermittent fasting help you lose weight? This is after all the most common reason people try IF in the first place.
The good news is that intermittent fasting has been found to be a good way to lose fast and importantly, to maintain weight loss. (26)
The fundamental way to lose weight is simply to consume less calories than you burn. With intermittent fasting, by reducing your eating window during the day, people tend to naturally consume fewer calories in the time frame that they are eating.
With less time available to eat, habits like snacking and grazing are compressed into a shorter time. In particular if you go for a longer fasting split, for instance a 4 hour eating window with a 20 hour fast, many people will find they simply can’t eat as many calories as they used to in such a limited time frame.
But beyond that simple change, intermittent fasting can also create changes in hormones in the body which impact weight loss, as well as muscle retention.
Insulin levels are seen to reduce, whilst HGH (Human Growth Hormone) and Norepinephrine both increase. This shift from fat storing hormones to fat burning hormones can increase fat loss, whilst minimising the loss of lean body mass.
Short term fasting can increase your metabolic rate, with studies indicating an increase between 3.6 and 14% (27)(28). Rather than going into ‘starvation mode’ as some people think and your body slowing down, fasting can actually fire up your metabolism to burn more energy.
This combination of intermittent fasting helping you to consume less calories, whilst simultaneously increasing the amount of calories you burn, is the fundamental reason fasting can be a potent addition to your weight loss strategy.
The results from studies have shown great potential. Many show significant weight loss over the short-mid term, including notable reductions in waist circumference, a key risk area for disease likelihood. (29)
Retaining muscle whilst losing weight is another key advantage of intermittent fasting, as one of the key criticisms of many diets is the long term effect of losing significant muscle mass alongside fat.
This is the classic pitfall of yo-yo dieting, with each dieting phase the person also loses some muscle mass. When coming off of whatever diet they’ve been on, this reduced muscle mass reduces their base level of calories needed, so making it easier to overeat and regain weight.
Fortunately IF has been shown to improve muscle retention as compared to a typical calorie restricted diet. (30)
So if you were wondering whether intermittent fasting is good for weight loss, good news is that is. Just bear in mind that they key mechanism through which you’re losing weight is still the good old Calories In vs Calories Out equation – fasting isn’t an excuse to consume as much as possible during your eating window.
Rather it’s a tool to create some discipline around eating, with a couple of metabolic advantages as a bonus.
How Does Intermittent Fasting Work?
Fundamentally, intermittent fasting is simply stopping adding new calories into your body for an extended part of the day/week, to push your body to utilise your stored fats instead until you refeed. (31)
Pushing your body to use stored fats is perfectly natural and something we are evolved for, however in the modern world with such easy access to food it’s rare people go long enough without a meal to shift into a fasted state.
Why do you think our body’s put fat on when we over eat? Adding fat is our way of preparing for the times when we don’t have such easy access to food and need some reserves to keep us going.
We can be in one of two states; a fed state or a fasted state, fasting is the opposite of feasting and we need a balance of both for a healthy life.
When we eat, and in particular when we overeat, we consume more energy than is immediately needed and so our body goes to work storing some of this excess energy for use later should we need it.
This is one of the key roles of insulin in the body, enabling the storage of excess glucose in the liver and into fat cells throughout the body.
We store energy in two ways, both of which are connected with insulin. First is the storage of excess carbohydrates as glucose and eventually glycogen, which is stored in the liver, as well as in muscle tissue.
Our capacity to store this excess glycogen is very limited, and easily exceeded, particularly with regular eating throughout the day and a sedentary lifestyle that doesn’t burn through these reserves.
Once exceeded, this excess energy is then stored in the next best location, for longer term keeping. Excess glucose is converted into fat in the liver by a process called de-novo lipogenesis (‘making new fat’). This new fat is then stored in the liver as well as being transported to fat cells throughout the body.
So when we eat, or overeat, we initiate these two processes, and for many people they spend most of their day/lives in this process of laying down reserves for use later on (only never getting round to the using them up part!)
Common advice has been to eat regularly throughout the day, but this never gives the body the chance to get into a fat burning state. (32)
Fasting, is essentially the reverse process of what we’ve just described. When we stop eating for a while, our blood glucose falls as we use energy, and our body has to start looking for replacement energy.
First it goes back to the glycogen stores, kept in the muscle and liver. This was energy easily converted for storage and so can be easily converted back for use too.
Glycogen is broken down back into glucose for energy, and can keep us up an running for somewhere between 24 and 36 hours is we’re not doing anything too active to burn through these calories quicker.
Once these glycogen reserves start to deplete too, with a longer period of fasting, the body looks to it’s next energy supply, stored fats. The process is reversed, converted stored fat for energy. This process is more complex and so not the first choice, but as you progress further into the fast this becomes the main source of energy.
So we only have two postitions – a feeding, energy storing (high insulin) condition and the opposting, fast, energy using (low insulin) condition. Improving the balance of these, or tilting the balance in favour of burning energy is key the aim of intermittent fasting.
Types of Intermittent Fasting
Intermittent fasting is simply rebalancing your fasted and fed states to encourage burning of energy. The way in which you do this can be hugely variable and easily adapted to suit your needs. The key thing is that we’re trying to increase the amount of time in which you’re fasted and reduce the time that you’re fed.
How this is done breaks down into a couple of different approaches, short daily fasts; extended fasts a few days per week with otherwise regular eating on off days; or longer term fasts spaced out over the month between longer periods of regular eating.
The difficulty generally increases as you go through the list – you’re unlikely to experience any major side effects of not eating inside of 24 hours (besides a little hunger) But as we progress to 24 hour plus fasts and multi-day fasts the difficulty will increase.
Daily Fasting Methods
This is one of the easiest fasts to begin with, called 16:8 fasting as you will fast for 16 hour each day, and condense your eating window into 8 hours. This is intended as an eating pattern you can do everyday and is fairly straightforward to make into a habit.
In practice, the simplest way to incorporate 16:8 into your day is to simply skip breakfast, and have your first meal at lunchtime, with dinner at some point within 8 hours after that.
A typical routine therefore may be to eat lunch at 12:00pm, followed by dinner or your last meal before 8:00pm.
Many people find this easy enough to incorporate into their lifestyle and enjoy the simplicity of this approach.
A recent study showed this was an easy method to adhere to for subjects, and that participants naturally consumed an average of 350 fewer calories than a control group, even though there were no restrictions on what they could eat during their eating window. (33)
A common step up from 16:8 fasting is called the 20:4 method. This simply compresses the eating window even further.
Although research suggests that an 8 hour eating window leads to a reduction in calories eaten, 8 hours is still plenty of time for snacking and overeating.
By compressing the window down to just 4 hours, it becomes that much harder to overeat without fullness intervening. With little time for snacking, people will tend to snack less.
This timeframe is very flexible in how you shift the window throughout the day to suit your lifestyle. For some people, a morning eating window of 8am – 12pm works well, freeing up their evening for other activities.
For those with family it may be that they shift all their eating to the evening, from 5pm – 9pm, allowing them to eat dinner with their family and still leave a little time in the eating window for a snack in front of the television with the kids.
OMAD – “ONE MEAL A DAY”
The logical conclusion of the shortening daily fast routine is the so-called OMAD approach, or one meal a day fasting.
This shouldn’t need much explanation – as you compress your eating into one meal, virtually eliminating the chance of overeating calories.
The harder task here is actually eating enough calories, so it’s important that meals are highly nutritious, with healthy greens etc, as well as sufficiently caloric. For sustained, healthy weight loss, a caloric deficit of around 500 calories per day is recommended.
Variable Day Fasting
ALTERNATE DAY FASTING
Moving into longer fasts, we start with alternate day fasting. This method, as the name suggests follows an alternating schedule with one day of normal eating, followed the next day by a very low calorie day – generally with a maximum of 500 calories for the day.
This approach allows for days of regular eating, with no lifestyle change, alongside days where you do still eat, but in very limited amounts.
The 500 calories may be consumed at any time of the day. The premise is that you will still shift into a fasted state quite easily as the calories from you limited meals will be quickly burnt. But by still having the choice to eat, the psychological pressure of hunger and fasting can be reduced.
The 5:2 method is a well publicised approach, as popularised by Dr. Michael Mosley with his book “The Fast Diet”
Much like alternate day fasting, you have normal days of eating alongside days of consuming 500 calories or less. In this case you have two ‘fast’ days per week at 500 kCals.
These are usually not done consecutively, which gives you great flexibility into how you incorporate your fast days into your schedule, making this a simple diet to adhere to.
Much of the research into intermittent fasting has followed this type of protocol, making it a worthwhile approach to consider.
36 HOURS FASTING
This is a full day fast, where you’ll avoid food for a whole calendar day and a bit. This is generally done by finishing up with dinner one day, avoiding food for the entirety of the next day, before breaking the fast with breakfast (get it?!) on the start of day 3.
This adds up to about 36 hours without food, which can be a challenge for some, but is a surefire way of ensuring you’re body has burnt a bunch of stored reserves for fuel.
A longer fast like this isn’t something to be doing constantly, and is best added as perhaps a once weekly addition to your schedule.
Many people will do something like this on a monday, with their last meal sunday evening, and having breakfast on tuesday. This is a great reset button if you over indulged on the weekend, with monday being the least likely day have social engagements for many people, making skipping meals a little easier.
This article is focussed primarily on intermittent fasting, as a tool you can use daily/weekly and build into a habitual practice easily.
There is the option to experiment with longer fasts, beyond 48 hours, but these come with the need for a little more prep, including a check with your doctor beforehand as this is a bigger stressor than short fasts.
Fasting for longer periods isn’t necessarily dangerous, done correctly. The world record for fasting was 382 days, but this was under careful medical supervision and not something to copy.
If trying a longer fast, don’t push things if you feel unwell, and it’s recommended to take a quality multi-vitamin for the duration. Also make sure you drink enough water during the fast, some people online appear to have been doing ‘water fasts’ avoiding water a well as food – this is dangerous and strongly discouraged.
Up to 7 days is within the realm of something you might consider doing at home, any longer than this is discouraged.
As you can see there are so many options for fasting that there should be something for everyone.
You can also mix and match these techniques to suit your schedule and lifestyle. One example is my own regimen as follows:
- Tuesday – Friday – 16:8 daily fast (first meal 1pm lunch at the office, last meal by 9pm at home)
- Saturday – Sunday evening – eat regularly (socialising, eating out etc.)
- Sunday evening – Tuesday Lunch – 36 – 40 Hour Fast
This approach allows me to let loose at the weekend, with a longer reset fast on monday to compensate, followed by moderate daily fasting for most of the working week. This fits my schedule well and gives me freedom with what I eat in my feasting stages, safe in the knowledge that I’ll be cancelling out any over indulgence with fasting elsewhere.
Intermittent Fasting Tips
So you’re keen to start intermittent fasting? Here’s a few top tips:
- START SLOWLY: It may be tempting to jump straight into a 48 hour fast to kick start your weight loss, but slow down! At first it may be best to ease into fasting, perhaps by skipping breakfast and working up to a 16:8 style fast. Work your way up to the routine or schedule that works for you but don’t jump in at the deep end.
- GIVE IT TIME: Your first few days of fasting may be a little rough, hunger is a strong feeling to shift, but with practice you’ll find it gets easier to control. Give IF at least a few weeks or a month to see if it’s working for you, and if it’s working for your weight loss
- KEEP DISTRACTED: Truth is, initially at least you’re going to get hungry. The best thing you can do is keep yourself busy and distracted until the sensation goes away.
- DRINK WATER, TEA, BLACK COFFEE: We often mix up hunger and thirst, and one of the best ways to subdue any strong hunger pangs is to fill up your glass. Green tea or black coffee in particular are great whilst fasting, and come with added weight loss benefits. (34)
- PLAN TO AVOID TEMPTATION: If you’re planning to do a 36 hour fast, don’t book in a drink with friends or a trip to the cinema on that same day! – you want to make it easy to avoid eating so avoid the types of social situations that may encourage this.
- DON’T BINGE STRAIGHT AFTER FASTING: You may be tempted to eat a huge meal at the end of your fast, after all, you’ve earned it right? Well just know that this is a recipe for digestive troubles. Ease back into food with a light meal, especially after longer fasts. Many people recommend bone broth as an ideal re-entry into eating after long fasts.
- COMBINE FASTING WITH A LOW CARB / KETO DIET: Eating a low-carb or ketogenic diet in between fasts will set your body up for burning fat efficiently. You’ll find that fasts become easier with less hunger pangs and more constant energy throughout your fast when combined with this way of eating. (35)
- ADD LIGHT EXERCISE TO YOUR FAST: If you’re fasting to lose weight, adding in some light exercise can be great to kick start fat burning. Try going for a long walk or a gentle jog early on in your fast, to burn through remaining glycogen reserves and kick start fat burning. High intensity exercise on the other hand, especially later on in your fast may be best avoided until after you’ve broken your fast.
What Can Be Consumed During A Fast?
The basic rule for fasting is that you are avoiding calories. You certainly aren’t avoiding liquids, as this can be dangerous. So here’s what you can have:
- WATER: Aim for at least 2 litres of water per day, it’s important to stay well hydrated throughout your fast. Still or sparkling is fine, just avoid flavored waters with any sugars.
For some flavor try adding a squeeze of lemon or lime, or infusing some cucumber for a more satisfying drink.
- TEA: Any type of tea is great whilst fasting, just don’t add sugar in and the calories it brings. Green tea in particular is recommended, as this includes compounds which suppress appetite, as well as having useful properties for weight loss if that’s your goal.
- COFFEE: Any type of coffee is fine, it’s what’s added to it you need to be mindful of. Avoid milky lattes etc. in flavor of black coffee. Cold brew or black iced coffee can be great, especially in summer. Again avoid adding sugars or sweeteners.
- BONE BROTH: This is a popular choice amongst seasoned fasters. This is a broth make from beef, pork or chicken bones and is a nutritious but low calorie addition that comes with plenty of minerals, vitamins and electrolytes. There are plenty of recipes online and this is highly recommended if you find yourself with strong hunger pangs.
Keto and Intermittent Fasting
Can you combine intermittent fasting and the keto diet? Yes, most definitely! These two, hugely popular dieting approaches are actually well suited to being combined.
Intermittent fasting is a great tool for simplifying your food choices (by making less of them!) and fundamentally is about getting your body to use up any carb reserves and start burning fat.
The keto diet does a similar thing, restricting your intake of carbs in the first place to ensure that fat becomes your main fuel, burning through excess reserves and the fats that you eat as part of the diet.
The two complement each other; if you’ve been fasting for a while, your body will have become more accustomed to shifting to burning fats for fuel, and going for extended time without carbs. This adaptation can make going into the keto diet that much easier, avoiding many of the early side effects.
Likewise, if you’re on a keto diet and fat adapted, adding in fasting to the diet to break through weight loss plateaus can be a great trick.
The best part is that as you’re already low carb, and burning your reserved fats for fuel with ease, you should find that the hunger pangs and fatigue that can come with fasting are much reduced when combined with a keto diet.
Starting the keto diet can be tough, which is why I recommend starting out with intermittent fasting first, working up to a 16:8 fasting pattern for a couple of weeks before starting keto. I’ve found that this makes starting keto much easier with fewer side effects.
Safety and Side Effects
Done properly, fasting for relatively short periods of time is safe, with minimal side effects. Most of these will tend to reduce with experience, but if you are unsure or feeling particularly acute side effects, stop your fast and consult your doctor before continuing.
- CONSTIPATION: This is common when first trying fasting. Be sure to drink plenty of water and try to add plenty of fiber to your meals during the eating window.
- HUNGER: This is an obvious issue when you go without eating for a while. This may be a little uncomfortable at first, as you’ll be consiously fighting the urge to eat. This does go away with experience, and learning that being hungry isn’t the end of the world is an important part of resetting your relationship with food.
- HEADACHES: Another common side effect for people just starting out with fasting. Adding a little extra salt or electrolytes into your diet and staying well hydrated should help.
- STOMACH CRAMPS: Comes with the hunger, sip water regularly throughout the day
- WEAKNESS/FATIGUE: On a short 16-24 hour fast this shouldn’t be too big a problem. Expect some fatigue if you’re trying longer fasts for the first time. This tends to subside as you become more adapted to burning fat for energy.
- DIZZINESS: It’s easy to become dehydrated whilst fasting, which is why drinking water regularly is important. Adding a little salt to your water when you’re fasting can help.
- JITTERS / ANXIETY: Fasting can increase production of the hormone adrenaline, one of the factors that boosts our metabolism. However this can also make us feel jittery and anxious, as if you’ve had too much coffee. This will likely subside with experience, so takes things slowly and build up to longer fasts incrementally
Fasting For Women
Fasting can work well for women, and for weight loss studies show similar levels of weight loss for both men and women. (36)
But when it comes to our biology, men and women do have many differences and so respond to interventions such as intermittent fasting in different ways. (37)
There have been some reports of women’s mentrual cycles being disrupted when intermittent fasting, returning to normal when eating normally again. For this reason it is best for women to ease into IF rather than going straight into extended regular fasts. Start with a 12-14 hour fast and work up gradually, easing back should you notice any issues and stopping immediately if there are any menstrual changes.
Intermittent fasting is not recommended for those who are pregnant, breastfeeding or underweight.
Frequently Asked Questions
Here are some common intermittent fasting questions and answers:
WILL FASTING CAUSE MUSCLE LOSS?
This depends on the length of the fast and the individual, however one study has shown that fasting led to less muscle loss than calorie restriction when compared. (38)
Initially your body breaks down glycogen for energy, whilst ramping up fat breakdown to replace it. Excess amino acids may also be used, which are the building blocks for protein and muscle. Muscle tissue itself however is generally conserved.
It’s important to maintain moderate protein intake in your diet during eating windows, and lifting weights regularly will help with muscle retention.
There have been studies suggesting lean people are at an increased risk of losing lean body mass while fasting, with a potential reduction in metabolic rate. But this is not such a concern for those that are obese and looking to lose weight. (39)
WHAT SUPPLEMENTS SHOULD I TAKE WHEN FASTING?
You can continue to take supplements whilst fasting, but on a short fast or intermittent daily fast you shouldn’t need any additional supplementation. Be aware that any fat-soluble vitamins should be take with meals rather than during the fast itself.
IS SKIPPING BREAKFAST UNHEALTHY?
This is a common misconception but isn’t necessarily the case. Many of the statistics around those skipping breakfast and health outcomes fail to identify that many people that skip breakfast also have unhealthy eating habits elsewhere.
In controlled studies, which looks to isolate the effects of skipping breakfast alone, the outcomes are much more favorable with those skipping breakfast eating less overall and losing more weight than those eating breakfast daily. (40)
CAN YOU WORK OUT WHILE FASTING?
Yes, you certainly can though with a few caveats. You don’t necessarily need to eat before exercise to give you energy, but for high intensity activity you may want to wait until a couple of hours into your feeding window. (41)
Remember to drink plenty of fluids and replenish electrolytes whilst exercising in a fasted state.
CAN I DRINK LIQUIDS WHILE FASTING?
YES! You definitely should be drinking liquids when fasting. So called ‘water fasts’ can be dangerous (drinking no liquids).
Water, tea and coffee and other zero-calorie drinks are all fine whilst fasting (just avoid adding sugar to the tea or coffee! Milk and cream should generally be avoided, but a small drop won’t hurt.)
DOES FASTING SLOW DOWN MY METABOLISM?
Not likely. Short term fasting has been shown to increase your metabolism, only beyond 2-3 days are there signs of metabolism slowing. (42)
WHO SHOULD NOT FAST?
Avoid intermittent fasting if you fall into one of these groups:
- Underweight or having a history of eating disorders such as anorexia
- Under the age of 18
You may be able to fast but consult your doctor if you fall into the below groups:
- You have diabetes (type 1 or 2)
- You have gout or high uric acid
- You take any prescription medication
- You have any serious medical conditions
DOES INTERMITTENT FASTING PUT ME INTO STARVATION MODE?
This is a common misconception about what happens when you fast but isn’t the case for short fasts as done with intermittent fasting. Studies have shown increases in metabolic rate during the early stages of a fast. (43)
HOW SHOULD I BREAK THE FAST?
It’s best to go easy when breaking your fast, particularly if you’ve been fasting for a longer period (36 hours plus). Start off with a small meal, ideally nothing too rich straight away as you may otherwise find yourself with stomach ache or digestive discomfort.
IS FASTING THE SAME AS CALORIE RESTRICTION?
No, there isn’t any specific limitation on calorie intake when intermittent fasting, although most people tend to eat fewer calories overall when fasting anyway. (44)
Fasting is about when you eat whereas calorie restriction is what and how much you eat.
WILL INTERMITTENT FASTING HELP ME LOSE WEIGHT?
Highly likely. Many studies on intermittent fasting have found reliable weight loss and in particular fat and visceral fat loss. (45)
It’s likely that you will naturally eat fewer calories whilst fasting as has been found in many studies. (46) The basic weight loss math of more calories out than in will always win out in the end. With that in mind just be careful not to over indulge on your days off or during your eating window.
IS FASTING SAFE FOR CHILDREN AND TEENAGERS
Intermittent fasting can affect hormone levels and should not be utilised for those under 18 years old.