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Interested in Fasting? Here's All You Need To Know!

Fasting is becoming increasingly popular due to its proposed health benefits, mainly weight loss, but with so many different varieties, it’s easy to get confused. Here we provide an overview of some different varieties and what they involve.

In Western culture, it is a common idea that the daily food intake should be divided into three square meals: breakfast, lunch, and dinner, with the addition of two snacks (morning and afternoon). This has been suggested to help appetite control, and indeed the mainstream media message is to eat “five to six times a day”.

However, the number of meals is not a universal standard, and the traditional three square meals are, somewhat surprisingly, a recent behaviour. In fact it is fasting that has long been integral to many religious and ethnic cultures. However fasting has come a long way in the last number of years with the introduction of intermittent fasting (IF), time restricted feeding (TRF), and fasting mimicking diet (FMD). But what’s the difference between them all?

Intermittent Fasting

Currently, the intermittent fasting (IF) diet is gaining popularity. For many people, it is considered to be less restrictive compared to traditional methods of calorie restriction. There are also various methods of IF, and people will prefer different styles but the basic premise involves taking periodic breaks from eating. Some methods include 5:2 fasting, alternate day fasting and weekly 24-hour fasts.

The 5:2 fast was first popularised by British doctor and journalist Michael Mosley, after appearing in a BBC TV documentary in 2012 and the subsequent publication of his book ‘The Fast Diet’. The diet consists of a person eating a normal diet for 5 days in any given week (preferably within their recommended calorie requirements for each day), while the remaining 2 days of the week, the person eats only 25% of their daily caloric requirement for that day (or 500/600cals for female/male).

A person can choose which two days a week they wish to restrict their calories, as long as there is at least one full non-fasting day in between.

Alternate day fasting involves fasting every other day. For some people, alternate day fasting means a complete avoidance of solid foods on fasting days, while other people allow up to 500 calories. On feeding days, people often choose to eat as much as they want.

Weekly 24-hour fasts involve fasting for up to 24 hours once or twice a week with as much food as a person wants for the remaining days. People on this plan can have water, tea, and other calorie-free drinks during the fasting period. People may benefit from trying a 12-hour or 16-hour fast before transitioning to the 24-hour fast.

Time restricted feeding

Time restricted feeding (TRF) is another type of fasting that is gaining popularity. TRF is a daily eating pattern in which all nutrient intake occurs within a few hours (usually ≤12 hours) everyday, with no obvious attempt to alter nutrient quality or quantity. It may be used in three variants: 16/8, 18/6 and 20/4 with 16/8, consisting of a 16-hour fast, and then an 8-hour nutritional window. In a more rigorous approach, the nutritional window can be shortened to 4 hours. TRF is usually performed on a daily basis and does not need prescribed restrictions. Additionally, the fasting window may be planned during night time which makes it an easy one for people to add to their daily regime. The TRF diet is of special interest among physically active people due to reports on its effect on weight reduction while maintaining muscle mass.

Fasting mimicking diet

The fasting mimicking diet (FMD) is relatively new to the world of fasting and is still in its early stages of research. FMD provides a relatively high caloric content but is able to mimic many of the effects of fasting. The majority of its research has been carried out in mice but human studies are underway. The human FMD consists of a 5 day regimen providing between 725 and 1090 calories, with a macronutrient content selected to mimic water only fasting but a micronutrient content aimed at maximizing nourishment.

Health benefits

Whilst each specific form of fasting will have its own health benefits, there is a number of overlapping health benefits associated with them all. Fasting, in general, has been shown protect against many diseases that are currently on the rise and these include:

  • Diabetes

  • Cancers

  • Heart disease

  • Neurodegeneration including Alzheimer’s disease

  • Obesity

  • Hypertension

  • Asthma

  • Rheumatoid arthritis

Fasting protects against these diseases through various mechanisms but the key ones appear to be via a reduction in insulin and fasting glucose, inflammatory markers, certain growth factors and a reduction in body weight.

Fasting also has a positive effect on our gut health via the migrating motor complex (MMC). The MMC is a cyclic, recurring motility pattern that occurs in the stomach and small bowel sweeping residual undigested material through the rest of the digestive system; think of it as serving a ‘housekeeping’ role in the intestines. However the MMC can only be activated during a fasting state where food has not been consumed for at least 4-5 hours. A sign your MMC is getting to work is that growling, officially termed ‘borborygmus’, emitting from your stomach at usually the most inconvenient time.

Want to incorporate some fasting?

If you want to try incorporate fasting into your daily pattern, the easiest one to start with is time restricted feeding. If you are a snacker, start by cutting out your morning snack, then your afternoon snack until you are eating just 3 meals a day. Next, try aim for eating all your food within a 12-14 hour window; this might mean having breakfast later or an earlier dinner. Once you have got a handle on this, try reducing the eating window to 8 hours or even 4 hours if you eventually want to try 24 hour weekly fasts.

You should not try any form of fasting if you have diabetes (unless supervised by a health professional) or are pregnant or breastfeeding. It is also not suitable for children or the elderly.


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