Which type of fasting should you try?
With nutritional science constantly changing and all types of people from influencers to doctors bringing out new fad diets on a daily basis, it would be easy to dismiss the current rise in popularity of fasting as just another wellness trend. However, with an abundance of scientific evidence and new studies emerging all the time, many types of fasting protocols are shown to have fantastic and wide ranging health benefits.
Not only rooted in many traditions and cultures, but also our ancient physiology, thinking about when you eat, not just what you eat, may improve your metabolic function (1), brain health (2), reduce the risk of many chronic diseases (3) and slow down the effects of ageing.
Simply put, fasting can help you to access your body's own innate healing system.
Our ancestors as hunter gatherers, would have faced times of scarcity and needed to be able to manage lack of food. Therefore our ancient biology is adapted to starvation. In fact we have over 200 genes which help us to adapt and activate conservation systems, so the body can not only survive without food, but also help the body and brain to hunt and gather by increasing our cognitive abilities. If you think about it, you’d want to be extremely alert when you are hunting for food!
Although our biology hasn’t changed much from our prehistoric ancestors and still uses these mechanisms, we no longer have a scarcity of food in our modern day lives; but in fact the opposite. We have an abundance of food, easily accessible which the body is not adapted to deal with appropriately.
Benefits of Fasting
Many people turn to fasting for weight loss, and whilst research shows it may be beneficial for reducing body weight (4), there are an abundance of additional benefits to fasting that affect nearly every system in the body.
Over time, fasting can change your gene expression. This can control inflammation, increase our antioxidant systems, affect stem cell production, increase brain function, build bone density and repair cells.
Fasting for Gut Health
Optimal health starts in the gut and according to research, our digestive system benefits enormously from fasting. Many of us are aware that certain foods benefit our gut health, but an equally important function occurs when we actually stop eating. Our digestion has its own ‘housekeeping’ system called the Migratory Motor Complex or MMC, whose job it is to clean up undigested food particles, unwanted bacterias and enzymes and send them down to the colon to eventually be excreted out of the body (5). The MMC is activated around 2-3 hours after eating and importantly, only within a fasted state. As soon as food (even a snack) is eaten, the process stops and attention is diverted back to digestion again.
This clean up operation keeps our gut in optimal working condition and without it we see dysbiosis and imbalances in our microbiome, as well as a whole host of other issues.
A healthy metabolism begins on a cellular level, and this drastically impacts your overall health and how you feel. As we age however, our cells' ability to process energy decreases. Not only does this impact our weight, but also leads to ageing in the body and often the diseases associated with it.
Fasting is seen as a reset button at the cellular level; helping your cells to run efficiently which in turn, helps with longevity and healthspan (6). Whilst long term fasting actually appears to decrease your metabolism, short-term fasting can have the opposite effect.
Our mitochondria have multiple functions, however they are often described as the energy factories for our cells. The quality of our mitochondria therefore impacts the health of multiple body systems and tissues which need this energy to function, such as the cardiovascular, immune and musculoskeletal systems as well as our brain. One suggested benefit of fasting is the optimisation of mitochondrial health and function. The better they run, the better we run (7).
The different types of fasting
There are many ways to fast and therefore many ways to access these healing systems. The most popular are;
Time Restricted Eating (TRE); People often confuse this term with ‘16:8 intermittent fasting’ which is slightly different in the realms of scientific studies where the name TRE is used instead. People who practise time-restricted eating typically eat during an 8 to 12-hour daytime window and fast during the remaining 12 to 16 hours. With promising studies showing an impact on weight loss, metabolism, improved heart function and reducing the risk of chronic illness, time-restricted eating is popular as it aligns eating and fasting cycles to the body’s innate 24-hour circadian system - all without altering diet quality and quantity.
Intermittent fasting (IF) - True Intermittent Fasting usually has a component of caloric restriction. This may be a 24 or 36hr fast once a week to even a three day fast once a month. Some people practise this as alternate day fasting, which means eating normally one day and then eating either nothing or very little the next. The popular 5:2 diet uses this method of calorie restricted fasting over two days of the week.
Fasting Mimicking diet (FMD) - Again, these are calorie restricted, yet also focus on high quality foods. Developed and clinically led by Dr. Valter Longo at the USC Longevity Institute, a diet of around 800 calories a day for 5 days allows the body to get just enough energy, however it does not recognise that it is being fed. This causes the body to enter a prolonged fasting mode. It’s therefore proposed that the FMD may provide some of the benefits of extended water-only fasting, but without any of the associated risks and more manageable to complete.
Keto Diet - The keto diet can also be placed in this category as ketosis (the aim of keto) is essentially what your body does when we stop eating. We have around 2500 calories of carbohydrate stored in our tissues as glycogen. Once the body has used up this source of fuel, it then starts to burn its stores of fat. It’s helpful to think of fat as stored energy and when this is used, it provides a very ‘clean’ source of energy, especially for the brain. These ketone bodies can feed parts of your brain, reducing its glucose requirement significantly.
Although keto can often be used in conjunction with fasting to help get the body into this state of ketosis, you are essentially starving the body of carbohydrates so the diet is predominantly focused around fats and moderate protein.
What's the best option for YOU?
The important thing to remember about any dietary choice is that it is highly personal to each individual. Everything from our genetics, gender, age and lifestyle will determine what fasting protocol will suit you best.
Fasting for women
Women in particular need to be aware of their unique biology when it comes to fasting. Most of the studies performed showing the benefits of fasting have used animals, men and post menopausal women.
Women in childbearing years should be aware that fasting can have an effect on hormones. Evolutionary, when our bodies enter a prolonged fasted state it shifts hormonal function to stop menstruation and ovulation. Why? Because our body believes there may be danger or famine and will not prioritise making babies in this environment. It is key to keep an eye on your menstrual cycle when fasting to ensure you are protecting your fertility and adjusting your fasting windows to suit this. However, some fasting protocols for women have proven to have benefits for those who need support with insulin resistance driven hormone imbalances such as PCOS or oestrogen dominance (8).
Women who are pregnant or breastfeeding should not practise fasting except potentially an overnight fast, as they won’t gain the benefits and may well cause health issues for the baby and themselves. Quality of diet is much more important during this time.
What about the menopause? Intermittent fasting can help with several symptoms of menopause, including weight gain, insulin resistance, brain fog and mental health changes and is therefore seen as benefical.
Where to begin with fasting
That being said, almost everyone would suit a 12hr fast a day as this ties in with our circadian biology. This could look like dinner at 7pm and breakfast at 7am, which allows our digestive system and other body systems to repair overnight. It’s a great place to start as many people are in the habit of snacking or drinking late into the evening and can work on this first.
Time Restricted Eating for 14hours+ is also achievable for most and will benefit a large number of people. It has been shown to help sleep and repair overnight. Essentially the deeper your sleep, the better you heal. This could start with a 6pm dinner time and an 8am breakfast. To help you achieve this you can look at adding in some MCT oil to your morning coffee to prolong your fast until breakfast. When you start adding hours beyond this, it is important to then look at the suitability of fasting for you personally.
Those who are already underweight, have a risk of disordered eating, undergoing cancer treatment, have adrenal or thyroid issues may not be suited to fasting as it is a stress on the body. This also is a consideration for those already living highly stressful lifestyles. If you are working non-stop, not sleeping well or over exercising; fasting may not be a wise choice.
Keto can also be really effective for some people, but again isn’t suited to everyone. Studies have shown very promising results when used as a medical treatment for many illnesses from Type II Diabetes, Parkinsons, Alzhiemers and Epilepsy (9). Beyond this however, cycling the keto diet seems to have the best results rather than being on it constantly. Some people are also genetically predisposed to respond differently to saturated fats and again this will determine if they suit a high-fat diet.
Match the diet to your personal biology and lifestyle rather than the other way around.