The Intermittent Fasting Guide

Intermittent fasting has become increasingly popular over the last few years, and it's far from being a fad or a Hollywood starvation scheme. It's been idolised, criticised and misinterpreted: intermittent fasting does NOT mean punishment or starvation. Used correctly, it's can be a powerful tool to improve your wellbeing and regulate your body's hunger signals. Used improperly, it can be a trigger for yo-yo dieting patterns and eating disorders.

Intermittent Fasting Guide

The Intermittent Fasting Guide

We put together this short guide to help you if you are considering Intermittent Fasting, drawing on the latest research available, benefits, and sharing our own experiences and point of view from a holistic sports science & wellness approach. 

Intermittent fasting simply means there are times in the day/week when you eat, and others where you don't. Eating usually happens within a set window of time of 10-12 hours. Our goal today is to approach the subject of intermittent fasting with a holistic wellness point of view, using our experience, observation, and the available information to share:

  • The background of fasting practices

  • The benefits

  • How it works

  • The types of fasting

  • The risks & safety guidelines

Healthy eating habits

BACKGROUND: Where does Intermittent Fasting come from?

Fasting is as old as time. Not only does it form part of cultural practices (think of Lent and Ramadan) - but we can go further back in time to unveil a timeline of food availability and man.

  • 2020 AD -  97% of homes in developed countries have a refrigerator. Our refrigerator and pantry is stocked full of ready-made food. Cheap food is more expensive than whole foods. If these stores are empty, we can drive to the shops and restock. If we're really stuck, it's UberEats. Availability: 10. Effort: ZERO. 
  • 1959 AD - 13% of homes have a refrigerator, pantries are stocked weekly. Canned ready-meals emerge but most meals are created from scratch (if you're really posh, by the house cook). Availability: 8. Effort: TWO. 
  • 1500 AD - A cupboard or pantry will store the scarce amount of food you can afford. You'll be lucky if you see more than soup and bread. Eating meat is a yearly occasion. If you're lucky, you have a goat/cow to use for dairy, and a chicken or two. If you're really, really posh, you have an ice-box and a team of cooks. You can buy food by trading or coins at the market. More advanced food preservation is possible by way of pickling and salting. Availability: 5. Effort: SIX
  • 10,000 YA - Agriculture kicks off; you work and eat off the land. Your community grows all of the available sources of food, which you can trade (or fight for). You start making more than you can eat, so man thinks of more clever ways to preserve food (such as smoking it). Availability: 5. Effort: SEVEN
  • 400,000 YA - Hunting becomes a little easier. At least now you have pointy wooden sticks (spears) to fish and hunt. You eat what you can, when you can - but when you kill a woolly mammoth you realise you need to preserve it (such as drying it). Availability: 3. Effort: EIGHT
  • 1.9 million YA - Hunter-gatherers need to live by the philosophy of "carpe diem" - seize the day, and more importantly: eat what you can seize. Children and women pick for berries and edible plants, while the men throw sticks and stones to catch fish and small animals (remember, spears have not yet been invented). Availability: 2. Effort: TEN
Intermittent Fasting | Excessive Food Availability

How is this relevant to Intermittent Fasting?

Food availability versus effort has a direct consequence to our health. To understand WHY intermittent fasting can be so beneficial to our bodies, we need a little perspective. In the last 50 years, food has become increasingly available and requires no effort to be obtained. Yet over 1.9 million years, our bodies have evolved and adapted to the scarcity of food and the effort (movement + energy) required to provide it. BUT WE'RE EATING LIKE IT'S CHRISTMAS. Every. Damn. Day.

Essentially, affluent modern man:

  • Eats too much and moves too little
  • Eats too many calories but too few nutrients
Is the paleo diet healthy?

What would PALEO humans think of our modern diet?

Benefits of Fasting

Being in a state of constant digestion is not only unnatural for our body, but it's highly problematic. Do you ever have your laptop on constantly, with a million windows open, without allowing it to switch off or re-boot? (I'm guilty here!) Our digestive system is pretty similar. It takes an average of 36 hours for food to go through the "full circle of life" from the yummy chewing part until the, ahem, exit. That's a day and a half of mechanical and chemical grinding, separating, organising, and storing. Now imagine this entire process having to restart EVERY TIME YOU EAT SOMETHING. That is your digestive system operating at full speed, all the time. It's like opening a new window on your laptop without ever closing it, and keeping your insulin levels high (hello, insulin resistance!) which leads to chronic inflammation.

Research concerning intermittent fasting (either as a health or spiritual practice) has shown mixed results concerning health and weight loss. There are many claims which are founded on mixed research (both on humans and animals) - but what ARE the things we can actually rely on? Fasting:

  • Provides a digestive rest - It ensures your digestive organs take a break, reducing the stress on your body. People with digestive discomforts find that a digestive rest can minimise irritation.
  • Regulates hunger - A gradual, consistent change in eating patterns regulates ghrelin and leptin, our hormones responsible for hunger and satiety (see below).
  • Reduces calorie intake - Even without this being a specific goal of fasting, minimising your eating window reduces the opportunity for excessive snacking and volume of ingested foods. You'll find you simply cannot eat as much!
  • Boosts your energy levels - At the start of the fasting practice and towards the last hours of your fast, it's normal to feel a little lethargic. However, as your body adapts you may notice peaks of mental and physical energy in the middle of your fasting phase - even during exercise. 
  • Supports the immune system - By giving our digestive system regular breaks, our body is able to direct more energy toward servicing our various immune cells, ensuring they're always ready for a fight against pathogens that may find their way in. 
Ghrelin and Leptin explained

Our frenemies, the hunger hormones..

Benefits of Intermittent Fasting

Appetite control: Fasting can be a simple but highly effective strategy for weight loss and eating impulses. It invokes less confusion by giving more precise instructions; it does not restrict food groups or require calorie counting. Instead, it relies on regulating two hormones, which will determine our hunger levels, regardless of what our body really needs:

  • GHRELIN: Feed me! The hormone responsible for those hunger pangs (AKA being HANGRY) is usually released into your bloodstream when it expects a meal. When you teach your body to expect food fifteen times a day, guess what...your ghrelin monster manifests itself more often, and you end up feeling hungry all day. Ghrelin is released by your gut to say "HEY, FEED ME!" when it expects food, usually around 30 minutes before your usual eating times. What's interesting is that after this initial hunger pang (AKA a ghrelin tantrum), the ghrelin will dissipate for a few hours - even if you don't eat - and return at your next scheduled meal time. Training your stomach to be more patient gradually DELAYS the release of ghrelin for longer intervals, meaning you start feeling hungry less often.

  • LEPTIN: Your tank is full/empty. Leptin, produced by fat cells, is released based on the nutrient value of the food ingested. Leptin signals to the body that you are satiated, or have received enough nutrients for now. The "tank" does not consider the calories in a meal; rather, leptin responds to the nutritional value of that meal. 1 tub of Ben & Jerry's ice cream = high volume of calories, low volume of nutrients = low leptin; hunger levels stay high. 1 tub of vegetable/meat stew = lower volume of calories, high volume of nutrients = high leptin release; hunger levels drop. Remember: your "tank" gets filled with nutrients, not calories! If your tank is empty, you'll still be hungry! After a period of fasting, leptin levels have been shown to rise faster after mealtimes, indicating that you're likely to eat less before you feel satisfied.
Health benefits of intermittent fasting
  • Cellular regeneration & immune system support: Caloric restriction in the form of intermittent fasting activates cellular AUTOPHAGY, which is our body's cell recycling system. Autophagy directs the cleaning up of damaged or unnecessary cellular material in order to allow the regeneration of newer, healthier cells. (Picture demolishing a derelict building in order to make space to build a new house.) More and more evidence has shown that dysfunctional autophagy contributes to various human diseases such as cancer, while improved autophagy boosts our immune system as it allows the body's immune cells to always function at their strongest. Intermittent fasting also helps us live longer! 

  • Energy adaptation: Your muscles, brain, and automatic bodily functions require energy throughout the day. Instead of relying on calories in the bloodstream, your body adapts to source energy from your fatty tissues during your fasting phase. This means it can help to boost both energy AND fat loss. 

If you do not have much fatty tissue, the energy can start to break down muscle tissue. However, this only really occurs with PROLONGED fasting - this is highly unlikely to happen if you're fasting for a few hours per day, unless you are a professional athlete.

How long should Intermittent fasting last?

Intermittent Fasting Guide

Different approaches to Intermittent Fasting

There are different types of fasting protocols which can be part of a lifestyle approach, and others which are more extreme and should only be prescribed and completed together with the supervision of a medical professional.

  • The 5-2 and the 16:8 fasts can be incorporated as part of your ongoing lifestyle 
  • 20:4 and 24-hour fasts are not advised for newcomers to wellness & fasting
  • 48-hour and any other specialised fasts and protocols should only be administered by a MEDICAL professional, and conducted under supervision. 


  • 5-2      5 days eating normally               2 days eating restricted: one 600kcal meal
  • 16:8    16 consecutive fasting hours       8 hours - choose based on lifestyle & preference
  • 20:4   20 consecutive fasting hours       4 hours - choose based on lifestyle & preference
  • 24*     24 hours consecutive fasting       Resume eating normally the next day
  • 48*     48 hours consecutive fasting       Resume eating normally the next day

*These fasts are considered extended fasts rather than intermittent fasts

Intermittent Fasting Guidelines

Intermittent Fasting Guidelines

Guidelines and Approaches to Intermittent Fasting

GUIDELINES & SAFETY: How long will it take for your body to adapt to the new fasting patterns? This will depend from body to body, but it's likely to take 7 - 10 days, as long as you follow these essential management & safety guidelines:

  • Hunger - Going from 100 to zero is a sure way to trigger the ghrelin monster and make you suffer. Gradual adaptation of hunger tolerance is key to a pleasant experience with intermittent fasting. Increase your fasting times by delaying meals by 15 minutes each day instead of throwing yourself straight into the deep end. Your body will appreciate it, and better tolerate the gradual adaptation.

  • Dehydration - If it's a food fast, it's not a fluids fast! Don't underestimate the amount of water you get from your food: while you're fasting, you usually need to drink more than usual. Water, tea, coffee (within reason!), and infusions can be ingested during the fast. Very small amounts of creamers and low-calorie drinks/blends can be ingested during your fast (such as vegetable broth). The key is: all foods should be liquidised (so there's no mechanical digestion involved) and carbohydrates (sugars) are strictly off-limits for the fast to be optimal. Aim for a maximum limit of 100kcal from ingested liquids during your fasting window, in order to still get the greatest number of benefits. 

  • Lack of concentration/dizziness/low blood pressure - Avoid fasting if you have a highly physical workload. Sudden fasting or pattern fasting (5:2, alternate day, or 16hrs+) can cause dizziness as your brain body struggles to source energy. Regulate your energy levels and always consult with your doctor if you're unsure. 

  • Social/family life - Integrating cultural/family/social life is important as a holistic (global) approach to our health. Being meticulous about your diet while compromising your social/family interactions can strain your mental wellbeing. Balance is key, and so is finding a solution that will work with your weekly schedule. 

  • Overeating/not chewing - Overeating or eating too fast during your eating windows can cause indigestion and an excessive calorie intake. Break your fast gently with a glass of water 30 minutes before consuming solids. Eating mindfully and enjoying your food becomes something to look forward to when you're intermittent fasting: take some time to really savour and digest during your feeding times!

  • Under-eating/triggers for eating disorders - Fasting is NOT a control strategy or a punishment. It's not designed to be a restrictive method that is bad for your health. Intermittent fasting relies on the fact that you have an eating window, and that you enjoy and fully digest enough nutrients during your eating windows. Avoidance or excessive control during the eating windows is not an intermittent fasting method and will be damaging to your health. If you have uncomfortable feelings about eating during your windows or purging, or you suspect a loved one may be suffering from an eating disorder, intermittent fasting should be avoided and all food-related barriers addressed with the help of a qualified medical professional. 

  • Stress Levels: high cortisol - Cortisol hormones are released under stress, and fasting can be a stressor on the body, which can even lead to weight gain as your body packs on body fat when you DO eat to avoid going into starvation mode. If your body finds it too stressful to cope with fasting (and releases excessive amounts of cortisol), intermittent fasting or longer fasting may not be the right strategy for you. It's best to work with your physician to adapt your eating regime to work with your health needs.  
Is intermittent fasting healthy?

Guidelines and Approaches to Intermittent Fasting

OUR RECOMMENDATION: Taking into consideration safety, the available research, and our own experience with fasting, we express our point of view from a HOLISTIC WELLBEING standpoint. 

We cannot rely on intermittent fasting to solve medical problems or bank on long-term beneficial effects. What we CAN do is consider the existing research, observe and consider the biological history of our evolution, and be mindful of our internal environment and the enjoyment and benefits we observe when fasting. 

A sharp change in your eating habits is likely to trigger hormone imbalances, hunger, and yo-yo diet practices. The body needs time to adapt to most stimuli (whether it's training or eating) - so giving yourself time to adapt any new regime allows your body to biologically adapt and regulate towards a goal. This practice can be compared to a progressive overload type of training in sports or fitness training, which start should always start slowly and gradually build up our training load and duration; so start small! Shorten your eating window by 30 minutes over a few days rather than starting out by chopping your feeding window in half. 

Over time, your body adapts to new habits. Even though the alternate day, 24-hour or 5:2 diet can be useful once in a while, it won't be as beneficial to regulate your body's routine and you may struggle with the fasting practice more. 

Instead of "fasting" (which can be given a negative connotation or seen as punishment), approach this practice as a daily "gut break" - give your body some time on and off. Regarding a mechanical break, there is not enough evidence to suggest that longer fasts are more beneficial than daily breaks: but there are more risks and the experience may be far from enjoyable. Remember an intermittent fast is designed to reward your body with a break...not to punish it! 


Before you decide to embark on a fast or a new food regime, always, always, ALWAYS consult a medical nutritionist for advice - or ensure you have completed some type of food intolerance/metabolic testing to ensure the eating pattern and foods you include are beneficial to YOU. Remember: every body is different, and any changes you make through your eating habits will have a direct effect on your internal environment!

Jessica Christensen

Jessica Christensen - Writer & Academy Director

Jessica is a holistic sports science & training specialist and industry innovator in the sports, fitness, and wellbeing education sector. With over 15 years of experience, her studies include NASM (National Academy of Sports Medicine) Harvard Medical School HMX Physiology, L4 Advanced Anatomy & Physiology, Evolutionary Biology, Philosophy of Science, TQUK L3 Award in Education, with continuing studies in evolutionary biology and sports science USCCE Accredited Program Director.

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