Intermittent fasting has become increasingly popular as a convenient way to lose weight without restricting what you can eat during feast hours. There are several different methods of intermittent fasting, one of the most accessible being the 16:8, which alternates between 16 hours of fasting overnight and 8 hours of feasting during the day  making it easy to incorporate into everyday life.

What is 16:8 intermittent fasting?

Back in the hunter-gatherer days, human beings had to survive natural cycles of food scarcity. Physiological adaptations such as storing food as fat in the adipose tissue was an effective way to fuel prolonged fasting periods [1]. From the advent of agriculture to modern-day globalisation, the explosion of food production has provided people in high-income countries with almost unlimited access to high-calorie convenience food. Eating around the clock goes against our evolutionary biology and, combined with the sedentary lifestyle of modern life, has resulted in a growing obesity pandemic, with the leading causes of global mortality being ischaemic heart disease and stroke [2].

Used as an obesity treatment in the 1960s, intermittent fasting has become a popular lifestyle approach for weight loss that involves scheduled periods of eating and fasting. There are several types of intermittent fasting methods including the 5:2 (5 days of unrestricted eating accompanied by 2 days of calorie restriction throughout the week), the one meal a day (OMAD) (as the name suggests, eating one large meal for the whole day), 24-hour fasts (which starts from your last meal until the same meal the following day, e.g. fasting from breakfast to breakfast) and finally Time Restricted Eating fasts (TRE) (alternating between hours of eating and hours of fasting) [3]. TRE fasts vary in length and difficulty, starting with the 12:12, a balance between 12 hours of fasting and 12 hours of eating that is ideal for beginners.

Then there is the 14:10, which enables the physiological benefits of fasting as well as the weight loss benefits seen in shorter fast periods. The 20:4 is an extreme form of caloric restriction that limits eating to a small four hour window. The 16:8 method is one of the most common TREs that provides a happy equilibrium between the beginner’s 12:12 fast and the more intensive 20:4 [3]. It is a daily fast that involves eating for 8 hours before fasting for 16, following the body’s natural circadian rhythm that controls the metabolism.

Weight loss benefits of fasting

The weight loss and health benefits of caloric restriction have been well documented and are achieved through the metabolic process of ketosis. Intermittent fasting promotes weight loss as it forces the body to switch from using blood glucose from food for energy to its own fat reserves, known as the G-K switch [1]. 12-16 hours in, fat is metabolised through the process of ketosis to produce ketones, which are then oxidised by the brain. As well as fat loss, intermittent fasting has other metabolic benefits including improved blood pressure, glucose regulation and heart rate —all contributing to better cardiovascular health [1]. Its more qualitative benefits include improved well-being, decreased hunger at night and a better relationship with food [3].

Health benefits of autophagy 

Restricting calories for longer periods has the additional health benefits of autophagy, during which cellular organelles are broken down and rejuvenated. Autophagy is a constant process that works in the background of cells; since it is also responsible for balancing limited energy sources during nutrient stress it can also be induced by caloric restriction. During fasting, the TOR kinase nutrient signalling pathway is deactivated, triggering autophagy. The cellular renewal that is associated with autophagy reaps many health benefits including protecting against cancer, neuropathies, heart disease and auto-immune disease — and may even boost longevity [4].

Read more about what happens to the body during fasting for weight loss here.

How to do the 16:8 intermittent fast

The 16:8 is an easy way of intermittent fasting that complements a busy schedule. It can be achieved by following the body’s natural sleep cycle and restricting calorie intake during the morning and evening. For example, passing on dessert or after-dinner snacks in the evening before skipping breakfast and breaking your fast with a well-deserved lunch is an easy way to practise the 16:8 fast and circumvents the prescribed tradition of eating three full meals per day. Adults usually require 7-9 hours of sleep to allow the body to recover and metabolise food consumed during the day. The body may need more sleep than usual during caloric restriction so prioritising long, quality sleep is integral. Indeed, lack of sleep is associated with increased levels of the hunger hormone ghrelin and decreased levels of the hormone leptin that indicates fullness, making fasting more difficult [5]. The 16:8 is easier to commit to than other methods such as prolonged fasting as it does not restrict your diet during feast hours. In fact, self-reported benefits of intermittent fasting include a healthier relationship with food during feast hours [3].

Practising the 16:8 comes with minimal risk, however new users may experience mild side effects such as headaches that should wear off as the body adjusts to being in a regular fasting state. Electrolyte imbalances can occur if your body goes without minerals for too long, leading to dizziness and lethargy. Risk of this can be reduced by taking dietary supplements or simply by adding a small amount of salt to drinking water. Hunger is a seemingly unavoidable side effect of caloric restriction, however hunger pangs tend to decrease the longer you fast for, with users reporting less overall hunger when practicing intermittent fasting [3]. The 16:8 intermittent fast has an advantage over quick-fix diets, being a sustainable weight loss method that can easily be adapted to your lifestyle for the long term.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7877980/
[2] https://www.who.int/data/gho/data/themes/mortality-and-global-health-estimates
[3] https://fasting.com/fasting-methods/intermittent-fasting/
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990190/
[5] https://fasting.com/moving-resting/fasting-and-fitness-what-you-need-to-know/