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To fast or not to fast? That is the question...

Fad diets have been a mainstay of the weight loss industry for decades, each season bringing with it a brand new quick-fix diet to help you shed a few pounds, lose a clothing size and achieve the “perfect” body. It would be easy to dismiss the recent surge in popularity of various fasting regimes as just another one of those fads, but to do so would be to ignore an abundance of scientific evidence and a rich history of cultural tradition that points to some not insignificant health benefits to be gained. Fasting in some form or another is deeply rooted in many cultures and religions, and research has shown that although there can be benefits for weight loss, there are an abundance of additional benefits to fasting that affect nearly every system in the body, ultimately leading to better overall health and prevention of chronic disease.1,2

Fasting for Gut Health

The gut is one such body system that benefits enormously from fasting according to the research. While most people focus on what happens in the gut when we eat something, equally important functions occur when we’re not. When we’ve finished eating, digestion goes into a kind of “housekeeping” mode, busying itself with the vital clean up operation required to keep the gut functioning optimally. Undigested food particles, enzymes and unwanted bacteria are flushed through the system towards the colon from where they can be excreted.

The system responsible for running the housekeeping is called the Migrating Motor Complex, or MMC, a series of involuntary muscular contractions that pulse in waves throughout the gastrointestinal tract, propelling food, waste and bacteria down through the body for excretion. It occurs approximately 2-3 hours after your last meal and continues for about 90 minutes, but importantly, this process occurs only in a fasted state. As soon as food is consumed, the MMC stops dead in its tracks and diverts attention away from the clean up and instead towards digestion.

Intermittent Fasting

Fasting therefore lends itself well to this clean up process, involving as it does the restriction of all or some foods or drinks for a period of time. In particular it is the practice of intermittent fasting, or time-restricted feeding, that can be particularly beneficial for the MMC. Intermittent fasting simply refers to the period of time that occurs between eating meals and is more correctly referred to as an eating pattern, rather than a diet as the types of food eaten are not restricted.

There are numerous methods of intermittent fasting that can be employed, all involving splitting the day or the week into eating and fasting periods. These include:
1) The 5:2 diet – involves capping your calories at 500 for two days a week, whilst continuing to eat normally for the remaining 5 days
2) Alternate Day Fasting – involves calorie restriction every other day whilst continuing to eat normally on the days in between
3) Time-Restricted Eating – involves set fasting and eating windows, for example the 16:8 method of only eating within an 8-hour window and fasting for 16 hours, and the 14:10 method of eating within a 10-hour window and fasting for 14 hours
4) 24-hour fasting – this method involves fasting for a full 24 hours and is only done once or twice a week
5) Spontaneous Meal Skipping – involves missing meals at random throughout the week.

The 16:8 Diet

Which method confers the most benefit to health is up for debate and will ultimately come down to a combination of the individual health goal and personal preference. However, for optimal daily benefits to digestive health and the MMC, some form of time-restricted eating is generally advised, giving the body a significant window during the day without eating in which to “clean up”. In addition, this form of fasting is arguably much easier to adopt as it avoids the necessity to go an entire day without food. For instance, with the right timing on the 16:8 diet, you can eat your last meal at 7pm and eat your first meal of the day at 11am the following day, essentially just delaying breakfast.

A New Prescription for Health

As well as demonstrable benefits for the MMC and gut function,3 research has shown fasting can positively influence our bodies on the cellular and molecular level too, causing human growth hormone levels to go up4,5 and insulin levels to go down,6 making it easier for the body to burn fat for energy (thermogenesis) and maintain a healthy weight. Cellular repair processes and healthy gene expression are also facilitated whilst fasting, helping to keep our cells healthy and protect against disease.7-10 Fasting has also been shown to have many inflammation fighting mechanisms too.11

With so many potential benefits to health, it’s clear that intermittent fasting should be considered as part of a healthy lifestyle regime, and in particular for gut health where normal bodily processes are unable to function optimally without regular periods of abstinence. With research still in its early stages, it will be interesting to see whether intermittent fasting becomes a more widely recommended practice in the future.

1. Patterson RE, Laughlin GA, Sears DD, et al. Intermittent Fasting and Human Metabolic Health. J Acad Nutr Diet. 2015;115(8):1203-1212. doi:10.1016/j.jand.2015.02.018[1]
2. Aly SM. Role of Intermittent Fasting on Improving Health and Reducing Diseases. Int J Health Sci. 2014;8(3):V-VI.[2]
3. Deloose E, Janssen P, Depoortere I, Tack J. The migrating motor complex: control mechanisms and its role in health and disease. Nat Rev Gastroenterol Hepatol. 2012;9(5):271-285. doi:10.1038/nrgastro.2012.57x[3]
4. Ho KY, Veldhuis JD, Johnson ML, Fulanetto R et al. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. J Clin Invest. 1988 Apr; 81(4):968-975 doi:10.1172/JCI113450
5. Hartman ML, Veldhuis JD, Johnson ML, Lee MM, Alberti KG et al. Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. J Clin Endocrinol Metab 1992 Apr;74(4):757-65
6. Heilbronn LK, Smith SR, Martin CK et al. Alternate-day fasting in nonobese subjects: effects on body weight, body composition and energy metabolism. Am J Clin Nutr. 2005 Jan;81(1):69-73
7. Alirezaei M, Kemball C, Flynn C, Wood M et al. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010 Aug 16;6(6):702-710. Doi:10.4161/auto.6.6.12376
8. Kim I, Lemasters JJ. Mitochondrial degradation by autophagy (mitophagy) in GFP-LC3 transgenic hepatocytes during nutrient deprivation. Am J Physiol Cell Physiol. 2011 Feb;300(2):C308-17. Doi:10.1152/ajpcell.00056.2010
9. Zhu Y, Yan Y, Gius DR, Vassilopoulos A. Metabolic regulation of Sirtuins upon fasting and the implication for cancer. Curr Opin Oncol 2013 Nov;25(6):630-6. Doi:10.1097/01
10. Martin B, Mattson MP, Maudsley S. Caloric restriction and intermittent fasting: Two potential diets for successful brain aging. Ageing Res Rev. 2006 Aug. 5(3);332-353. Doi:10.1016/j.arr2006.04.002
11. Longo VD, Mattson MP. Fasting: Molecular Mechanisms and Clinical Applications. Cell Metabolism Volume 19, Issue 2, 4 Feb 2014, pages 181-192.

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