Intermittent Fasting: The Complete Guide Including Medical Research

Intermittent fasting (I.F) is most commonly used as an aid for weight loss, however, intermittent fasting also has profound health benefits when conducted properly. Here is your complete guide to I.F for both men and women to help you start your journey.

This post will cover:

  • What is intermittent fasting?
  • Types of Intermittent Fasts.
  • Benefits of Intermittent Fasting.
  • The best hours to fast.
  • Best time to exercise.
  • How to start your fast.
  • What you can eat and drink.
  • Foods and drinks to avoid.
  • How to break your fast.
  • Who shouldn’t do intermittent fasting?
  • Medical references, research and studies on I.F
Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances

What is intermittent fasting?

Intermittent fasting is an eating pattern that involves omitting frequent meals from your daily or weekly routine. By alternating our cycles of fasting – using different methods such as the length of time you fast to how often you fast for – we can boost the bodies ability to lose weight and experience the profound health benefits of intermittent fasting, long term.

Fasting variations are necessary so that we don’t plato – it’s like going to the gym and doing the same workout routine every day, eventually, the body will stop responding and or making changes, therefore, to gain the maximum benefits of intermittent fasting, it is advised to switch it up on a weekly basis.

Types of intermittent fasts.

There are several types of fasting schedules available, however, I will focus on the top 6 most popular methods.

5:2 fast:

You eat as usual for 5 days of the week, and restrict your calorie intake to 500-600 for two days of the week. For example, you can restrict your callorie intake monday and friday eating as usual the rest of the days, or restrict your intake saturday and sunday. Personally, I find fasting – eating no food whatsoever – has more benefits than reducing your calorie intake.

16:8 fast:

You fast for 16 hours, drinking only water, and your meals are eaten within an 8 hour period. This is the most popular intermittent fast.

Omad fast:

You have one meal a day and eat your meals within a 2 hour period. As a result, you are fasting for 22 hours.

24 hour fast:

This fast is also known as Eat-Stop-Eat, and lasts for 24 hours. This intermittent fast cycle can be done once or twice per week.

Alternate-Day fasting:

Alternate-day fasting means you do not eat every other day, some people reduce their calorie intake to 500 on these days, however, if your goal is to improve your health and not solely to aid weight loss, not eating and only consuming water is always the best fasting method.

Warrior fast:

The warrior fast or diet was made popular by fitness expert Ori Hofmekler. This involves eating small amounts of raw fruits and vegetables during the day, and a large meal at night. In short, you fast during the day and feast at night, within a 4-hour window.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances

Benefits of intermittent fasting

There are numerous benefits to intermittent fasting, that are dependent on the length of time you fast for and your chosen diet that accompanies this fast.

Below is a list of the main health benefits that occur within the body during your fast.

Increases Our Human Growth Hormone (HGH):

An increase in HGH incurs tissue repair and is particularly beneficial for those who weight train. Always excersie before breaking your fast in order to optomise your results.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances

Metabolic Hormones:

Intermittent fasting stabilises our metabolic hormones such as insulin leptin and ghrelin that creates a hormonal balance and aids weight loss.

Insulin is a hormone made by the pancreas that turns sugar – also referred to as glucose – from carbohydrates into energy. Sugar can be stored in the body for future use as it is the most accessible fuel source the body has and when our sugar intake is reduced through fasting, the body will search for other energy sources; most commonly, fat. Using fat as an energy source means we are burning off stored fat that incur weight loss. Our blood sugar levels will also stabilise which is great for those who are glycemic, pre-diabetic and diabetic. However, more on that later.

Leptin is the hormone that regulates our body fat and energy balance by inhibiting our hunger. If we are obese or have an insulin resistance – found in type 2 diabetes patients – it means that our body has the inability to detect our hunger or satiety sensations, causing weight gain.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances

Ghrelin is what tells us when we are full, also known as the hunger hormone, so when these levels are high in the body, it doesn’t work. This is why a large percentage of dieters regain all the weight they lost within a year, due to the ghreline hormone that tries to maintain and re-gain fat.

I.F enables our metabolic hormones to work more efficiently by stabalising them. When our hormones are unbalanced, we can end up with severe chronic issues, in particular, diabetes.

Decreases Inflammation:

When we decrease the body’s inflammation, we decrease the pain we feel as a result. Fibromyalgia – that causes chronic pain – and chronic inflammatory issues such as rheumatoid arthritis, periodontitis and sinusitis issues will be reduced as a result of fasting.

“In the March 5th 2019 edition Cell Reports, the study reports on the health benefits of periodic cycles of fasting for people with inflammation and indicated that the diet – low calorie intake or fasting – reversed inflammatory bowel disease (IBD) pathology in mice.”

University of Southern California
Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances anti ageing


Who doesn’t want to look youthful? Estrogen, progesterone and testosterone are growth hormones associated with tissue and wound healing, anti-ageing. Boosting these hormone levels can benefit our overall well-being and make us feel and look better. Fasting balances out these hormones, decreases our insulin levels as mentioned above, that in turn lowers our estrogen levels in both men and women. Higher estrogen levels can lead to estrogen dominant cancers – which nobody wants – and boosting our progesterone levels can help women with symptoms of PMS which can be low in women. With men, this can boost their testosterone levels which increases muscle mass.

Increases Energy:

Statistically speaking, intermittent fasting can boost your energy levels by 10-15%, you will have less crashes as a result of your hormones stabilising and create what is known as sustainable energy. There are a lot of people who suffer from chronice fatigue – I was one of them – that turn to stimulants such as an excessive amount of coffe, in order to function. Allowing your body to utilize energy in other parts of the body whilst fasting is a healthier option, rather than grazing on food out of bordom or neccessity. Fasting is, of course, the best, natural mood stabilizer in this case.


Intermittent fasting allows the body to work at its best, this includes, enabling the body to utilize its natural detoxifying system. There are toxins everywhere, from what we eat, in our fabrics, our fire retardant clothing, dyes, and high levels of glycol that are linked to cancer.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances immune system

Improves Immune Function:

With autoimmune diseases on the rise, our immune systems are being destroyed, fasting is a medically proven way of resetting the immune system and often used for those who have recently finished cancer treatments such as chemotherapy. I go into more depth on this via my water fasting blog, for those interested.


Last but certainly not least, is probably the most important of all the benefits. Autophagy is known as Good Physiological Stress and in charge of our cell recycling. In as little as 13 hours into our fast- the average being 18 hours – our body breaks down old cells, reusing them for new ones. A build-up of old cells can, of course, cause cancer.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances what happens to your body when you fast best times to fast

The Best Hours To Fast

I found knowing this information very motivating and therefore worth mentioning; knowing the true benefits of intermittent fasting can help you remain focussed and personally, I found knowing how our bodies respond to intermittent fasting, really interesting.

Our blood ketones skyrocket around the 10th hour of our fast which makes us break down fats, sustain our energy and makes us lean.

Plasma free fatty acids are what breaks down our fat for energy that happens around the 12th hour mark.

Glycogen is the storing of sugar in the body that drops dramatically around the 12th hour because the body tries to find other energy sources to use.

Plasma insulin levels will decrease and then significantly drop before leveling out around the 13th hour; great for those who are pre-diabetic or have diabetes already.

Blood glucose levels will dip down and then stabalise around the 13/14th hour.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances

Best Time To Exercise

Studies show, that working out in a fasted state – meaning you haven’t eaten – allows the human growth hormone to work to your benefit. Working out after eating means the release of HGH becomes restricted by the rise of glucose – sugar – in your body.

Science Daily posted an article Routine periodic fasting is good for your health, and your heart that shows HGH production in males was up to 2000% and females 1300% after a 24 hour fast. Exercising in a fasted state, allows HGH and testosterone to create the best environment for burning fat and building muscle.

At first, you may not have much energy which is where black coffee comes in handy, however, in time, your body will adjust and you will feel more energised as demonstrated above.

How To Start Your Fast

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances meal plan

Personally, I jumped right in and my first fast lasted for 60 hours – you can read more on this here – however, my goal was to reboot my immune system with a view to doing this seasonally.

For beginners, it is recommended that you ease into it so you are not feeling every craving and hunger pain simultaneously. It is also suggested that you gradually decrease your intake of food from three meals a day to one meal a day – a sort of mind-body training excersie.

Lowering your carbohydrate intake is a good place to start as it will help you feel and be less hungry. You want to limit yourself to 3 meals a day with no snacking in between. Introduce healthy fats – stay away from saturated fats – such as vegetables, and grass-fed meats which will help you last longer between meals. Potassium and magnesium-rich foods will help heal the body and fight against insulin resistence. Fibre will feed the microbes in your gut that also help protect your cardiovascular system.

Let your body dictate when you eat. Do not confuse our satiety sensation that can be felt around 20 minutes after a person has already eaten with hunger, that manifests within a few hours of eating our last meal.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances drink lots of water

Assuming you eat a healthy diet, introduce a tablespoon on sea salt into your meals. You will be drinking a lot of water during your fast and throughout the week so it is important to consume sodium that will eliminate headaches.

Electrolites are important as they are high in potassium that give you energy throughout the day. Nutrients and vitamins are very important whilst fasting.

Prepare your food in advance because your body is not aware of man-made time, therefore, when it signals to you that you need to consume food, it may not be convenient. Bring the pre-prepared food with you so as to eat the correct foods whilst fasting.

What you can eat and drink.

If you have chosen to do what I call a pure intermittent fast, then no food is consumed during the designated fasting hours; drinking only water and black coffee – no milk, no added sugar, no sugar substitutes and no cream either. Otherwise, you will break your fast and possibly, unknowingly.

For those who wish to receive the weight-loss benefits of intermittent fasting, it is recommended that your meals should be low in carbohydrates and sugar eating meals that are rich in healthy fatsnot saturdated fats – a moderate protein intake and avoiding processed foods.

If you are over 30 years of age, maintaining a low carb and low sugar diet is especially as important because these food types will cause migraines, headaches and mood-swings; symptoms you want to avoid.

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances


  • Coffee – black coffee only
  • Tea – tea leas, antioxidant teas such as Chai tea and earl gray
  • Sparkling water – an alternative to still water
  • Apple cider vinegar – a shot in the morning delays hunger and has a pH balancing effect on the body.

Below is a general outline of foods to avoid and for those living in the United Kingdom, you will find a traffic light system image on all packaged food that will help with deciphering what is healthy and what is not.

Foods to avoid in order of importance:

Here is your complete guide to the benefits of intermittent-fasting with scientific research; various types of fasts, when to exercise, diet guide and tips. world of frances

Sugar: fizzy drinks such as Irn-bru, Coca-cola, Pepsi, Fanta including drinks such as fruit juices – these are high in fructose sugar, which your body absorbs directly into the bloodstream that when consumed in excess, can cause diabetes.

The agave plant, any and all sweets or candy, ice cream and many other products that contain added sugar – all ingredients are generally listed on the back of any packaging.

Refined grains: Wheat, rice, barley and rye, as well as bread, cereal and pasta. Reducing or eliminating your refined grain intake will prevent you from bloating too.

Artificially and Naturally Derived Trans fats:

Naturally-occurring trans fats are produced in the gut of some animals and foods made from these animals (e.g., milk and meat products) may contain small quantities of these fats. Artificial trans fats (or trans fatty acids) are created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid.

Trans fats raise your cholesterol levels, more specifically, what is known as your bad cholesterol called Low-density lipoprotein (LDl) that puts you at risk of developing heart disease, having a stroke and more commonly connected to type 2 diabetes.

Diet and low-fat products: Many dairy products, including milk, including cereals and crackers have fat-reduced options, however, they contain a ridiculous amount of sugar. My general rule of thumb is to avoid all marketing and go directly to the traffic light system as in the UK or check the ingredients.

world of frances foods to avoid junk food

Highly processed foods: Processed foods are meals that have been altered during preparation and can often include frozen, canned, baked or even dried foods.

Here are some examples of processed foods as per the British National Health Service (NHS):

Breakfast cereals, cheese, tinned vegetables, bread, savoury snacks, such as crisps, sausage rolls, pies and pasties meat products, such as bacon, sausage, ham, salami and paté. “Convenience foods”, such as microwave meals or ready meals. Cakes and biscuits. Drinks, such as milk or soft drinks.
Not all processed food is a bad choice. Some foods need processing to make them safe, such as milk, which needs to be pasteurised to remove harmful bacteria.
Other foods need processing to make them suitable for use, such as pressing seeds to make oil.


Starchy vegetables: It’s best to limit starchy vegetables in your diet if you’re view is to aid weight-loss. Starchy vegetables can include, kidney, black and cannellini beans, butternut squash, corn, chickpeas, lentils, peas, potatoes and parsnips.

world of frances brain junk foof

How to break your fast:

Whilst fasting, you are allowing your digestive system to undergo a period of rest and repair, so how we break that period is equally as important.

You wouldn’t wake a person up by throwing cold water over them, would you? Or maybe you would. Similarly, we don’t want to shock our system by allowing our hunger to take over; we want to awaken our digestive system gently.

world of frances healthy living juices

Dependent on the length of time you have fasted for, or the type of fast you have completed, will have an effect on the way in which you break your fast. For example, If you have chosen the 16:8 fast, you would take the first hour to gradually introduce food back into the system with something like a soup or foods that are low in carbohydrates and sugars.

Personally, I like to break my fast with whatever my body is craving, however, learning the language of your body is an entirely separate topic in of itself. As an example, when I crave broccoli, it means my body needs iron and so on and so forth.

Who shouldn’t do intermittent fasting and is it safe for women?

  • Adrenal fatigue – Mainly caused by too much stress in your life, those dealing with adrenal fatigue should balance out the adrenal function first, before beginning an intermittent fast.
  • Medications – When we are taking medication, we are forcing a physical alteration in the body, similarly, this occurs during an intermittent fast, therefore taking medications whilst on a fast may cause issues. It is always advisable to check with a health care professional.
  • Diabetes – Intermittent fasting can really benefit those with diabetes, however, if you are on medication, then the same rule applies – do not simultaneously combine medication with intermittent fasting.
  • High blood pressure – Get your blood pressure under control, adopt a good diet and then introduce intermittent fasting.
  • Nursing – It was believed that women who were fasting whilst breastfeeding would produce more milk, however, recent medical studies show that it will have the opposite effect and cut down your milk supply to almost nothing.
  • Pregnancy – Do not adopt intermittent fasting into your regime whilst pregnant; you have to eat more often when carrying a baby and fasting in this instance, is both unhealthy and unsafe.
  • Malnourished – If you are malnourished or have an eating disorder – even those who used to have an eating disorder – then do not take part in intermittent fasting as this can form a bad habitual pattern.
world of frances pregnancy

There is a lot of controversy over whether it is safe or not for women to do intermittent fasting as we are generally more sensitive to hunger. Women are designed to bea children and as a result, the body always considers that there is a potential fetus in the womb, which makes our hunger sensations, stronger. Intermittent fasting using the crescendo model – 3/4 days a week every other day or 2 days of fasting in a row – will allow the body to adjust better for women.

Nevertheless, if intermittent fasting, regardless of the type you choose, interferes with your menstrual cycle, immediately stop. It is vitally important to remember, for both men and women, that if your body is not responding to what you are doing in a healthy way – and you will intuitively feel the difference – then do not continue with the fast or anything that you are doing for that matter.

If you found this article on the benefits of intermittent fasting useful and informative, please share and subscribe to my mailing list. It is vitally important that everyone knows the effects intermittent fasting has on the body before doing so, to keep safe and informed.

Always check with a health care professional, in particular a nutritionist who can help guide and inform you personally.

Sending love and light,



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