Over the last decade, intermittent fasting has gained popularity in the media and research for its potential health effects. But what exactly is intermittent fasting and is it good for health?

What is intermittent fasting and history

Intermittent fasting involves regular periods of very little or no calorie intake. It is characterised as an eating pattern rather than a specific diet. Although intermittent fasting has gained recent popularity, fasting or abstaining from food has been around for a long time. In ancient hunter-gatherer times food wasn’t always abundant, so humans often spend long periods without eating. Fasting is also still common practice in certain religions such as Islam, Judaism, and certain denominations of Christianity.

There are various types of intermittent fasting regimes, each characterised by different fasting and eating patterns:

Benefits

Intermittent fasting has been linked to a number of health benefits for the body and brain.

1. Intermittent fasting can help with weight loss

Weight management is a commonly cited benefit associated with intermittent fasting. It differs from the traditional continuous calorie restriction method as the caloric restriction occurs periodically over a shorter period. Various research reviews on the topic have found that intermittent fasting regimes are a useful weight-loss tool [2-5]. However, when compared to traditional calorie restriction diets, intermittent fasting was not found to be superior for weight loss [2, 3]. This is because both methods result in a calorie deficit. In other words, over time you consumed less energy than you require, leading to weight loss. However, intermittent fasting may have additional benefits such an insulin control. 

2. Intermittent fasting may help to regulate blood glucose and insulin levels

Protection against type 2 diabetes has also been linked to intermittent fasting [1]. For example, a review including 8 studies found intermittent fasting led to improved blood glucose control and insulin resistance across the general population as well as in those with obesity or prediabetes. As these factors are associated with the development of diabetes, it would suggest intermittent fasting may be a useful preventative measure [4]. However, much of the research in this area is in its infancy [6]. Therefore, when it comes maintaining good blood glucose levels, a healthy balanced diet with minimal processed foods are recommended.

3. Intermittent fasting is associated with improved cognition and delayed ageing

A universal aspect of ageing is the accumulation of oxidative and metabolic stresses that results in the natural degeneration of cells. Research conducted in animals provides some evidence that intermittent fasting my help delay the aging process [7]. Intermittent fasting is thought affect cell stress response systems, thereby protecting the brain cells against the natural genetic and environmental factors which would otherwise affect our brains during aging [8]. In addition, analysis of human cells have shown that following an alternate day fasting period, activation of longevity-inducing genes were increased, and the human cells were more resistant to stress [9]. This provides some promising evidence for the potential beneficial effects of intermittent fasting on ageing. However, further research in humans is required to clarify how intermittent fasting may work across a wide range of participants.

Risks

Although intermittent fasting may seem harmless, skipping meals or not eating for a prolonged period can be dangerous, especially for certain groups of people – for example, children, pregnant women, breastfeeding women, those on medications, and those who have health conditions. It is always best to seek advice from a doctor or registered nutrition professional before making any drastic changes to your eating patterns.

Overall, fasting has several potential benefits with more and more research coming out about this new eating pattern. Observing not just what you eat, but when you eat can be a valuable tool for adjusting calorie intake and regulating key hormones relating to food. Just remember to start slow, listen to your body, and consult a healthcare practitioner to assist.

References:

1. 1. Patterson, R.E. and D.D. Sears, Metabolic effects of intermittent fasting. Annual review of nutrition, 2017. 37.
   2. Seimon, R.V., et al., Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and Cellular Endocrinology, 2015. 418: p. 153-172.
   3. Harris, L., et al., Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Evidence Synthesis, 2018. 16(2): p. 507-547.
   4. Cho, Y., et al., The Effectiveness of Intermittent Fasting to Reduce Body Mass Index and Glucose Metabolism: A Systematic Review and Meta-Analysis. J Clin Med, 2019. 8(10).
   5. Welton, S., et al., Intermittent fasting and weight loss: Systematic review. Can Fam Physician, 2020. 66(2): p. 117-125.
   6. Cioffi, I., et al., Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. Journal of Translational Medicine, 2018. 16(1): p. 371.
   7. Stockman, M.-C., et al., Intermittent Fasting: Is the Wait Worth the Weight? Current Obesity Reports, 2018. 7(2): p. 172-185.
   8. Martin, B., M.P. Mattson, and S. Maudsley, Caloric restriction and intermittent fasting: Two potential diets for successful brain aging. Ageing Research Reviews, 2006. 5(3): p. 332-353.
   9. Allard, J.S., et al., In Vitro Cellular Adaptations of Indicators of Longevity in Response to Treatment with Serum Collected from Humans on Calorie Restricted Diets. PLOS ONE, 2008. 3(9): p. e3211. 

Mayara De Paula, Nutrition Student

Mayara is a Psychology graduate currently completing an MSc in Clinical Nutrition and Public Health at University College London. She has volunteered with a number of charitable organisations providing recipes and nutritional advice. Her interests include health inequalities, child health and prevention of non-communicable diseases.