Intermittent Fasting – What’s the deal?
Intermittent fasting seems to be the latest craze in the world of health and fitness. In this article I will explain the different types of intermittent fasting and the proposed health benefits, mainly of time restricted feeding.
What is intermittent fasting (IF)?
IF is a term used to describe a whole host of eating patterns, but ultimately it describes abstaining from food, intermittently. As you can see, this definition is not objective, and therefore IF is a very broad term. Here are some of the eating patterns described by IF:
- Alternate day fasting – the diet is restricted (usually in terms of calories) on alternate days.
- Time restricted feeding – this describes a dedicated eating window during the day. For example, eating for 10 hours and fasting for the remaining 14 hours.
- The 5:2 diet – this is where calories are restricted to around 500 on 2 non-consecutive days of the week.
What do they all have in common?
All of the ‘diets’ or patterns of eating listed above describe some form of food restriction, whether in the form of time or calories. Much of the research around these areas highlight that they are all different forms of restricting calories consumed, which in theory is true as they limit the opportunity to eat.2 However, the research has looked further than purely calories in vs. calories out.
Let’s now focus in on time restricted feeding.
Remember, this eating pattern condenses the hours of the day spent eating, and therefore extends the fasting hours (where only water or hot drinks like black tea/coffee are consumed). Research (amongst mice) has shown that restricting the eating window to 8 hours (and fasting for 16 hours) showed protection against obesity, high insulin levels, inflammation and increased motor control, when consuming the same number of calories across the day, ad libitum.1
The authors attribute this to aligning with the normal cellular metabolic processes. These are intricate interwoven processes that occur within our bodies constantly, including nutrient sensing mechanisms and circadian rhythms.
The cycle of time restricted feeding (fast time usually >12 hours daily) allows the body dedicated time to repair and carry out ‘maintenance work’, without the added task of digesting and metabolising a constant stream of food, also suggesting possible benefits for gut health.4
A summary of the current research on time restricted feeding suggests that the health benefits include reductions in total cholesterol, glucose, insulin and inflammatory markers occurred despite variable effects on weight loss outcomes.3
What are circadian rhythms?
Circadian rhythms are physical, mental and behavioural changes that follow a daily cycle. Our daily circadian rhythms can influence our sleep-wake cycles, hormone releases (such as cortisol – our stress hormone), eating habits, digestion and body temperature, to name a few. Daily changes in light and dark are one of the main determinants of these rhythms. Disrupted or irregular circadian rhythms have been linked to various health conditions such as obesity, diabetes, sleep disorders and depression, for example.
The Bottom Line
There is emerging evidence to suggest health benefits of time restricted feeding, but it is important to remember that the research is in its infancy, and mostly carried out within animal models, with few human studies.
Here I have outlined some of the proposed health benefits of consuming food within a restricted window, however I would also like to highlight that you should always do WHAT WORKS FOR YOU!
I would generally recommend aiming to consume all food and drink within 12 hours, leaving time for a 12 hour overnight fast. This is very practical and maybe something you already do. This would reflect breakfast at 8am and finishing the evening meal by 8pm. If you are someone who constantly grazes and snacks throughout the day, especially late at night, then introducing some boundaries, such as a daily eating window, may be helpful.
But, as mentioned above, IF or time restricted feeding is not for everyone, and is not recommended or advised for the following population groups:
- Pregnant or breastfeeding women, this is a time to nourish your body for growth and sustaining another life
- Children, as fasting period may restrict them from thriving
- Have type 1 diabetes (or type 2 diabetes on insulin)
- Taking medications that require food
- Underweight, as this could lead to further weight loss (BMI< 18.5 kg/m2)
- Suffer or have suffered with eating disorders or unhealthy relationships with food
- Recovering from surgery, fasting may not provide enough nourishment for recovery periods
*** This blog post is not intended or implied to be a substitute for seeking professional medical advice, diagnosis or treatment. Information provided here is general and is not intended to treat, diagnose, prevent or cure any diseases or conditions. Please contact your GP or private health consultant if you have any personal health concerns, or consult a registered nutritional therapist for personalised dietary and lifestyle advice and guidance.
- Hatori, M., Vollmers, C., Zarrinpar, A., DiTacchio, L., Bushong, E.A., Gill, S., Leblanc, M., Chaix, A., Joens, M., Fitzpatrick, J.A. and Ellisman, M.H., 2012. Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Cell metabolism, 15(6), pp.848-860.
- Gill S, Panda S. A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans that Can Be Modulated for Health Benefits. Cell metabolism 2015
- Patterson, R. E., Laughlin, G. A., LaCroix, A. Z., Hartman, S. J., Natarajan, L., Senger, C. M., … Gallo, L. C. (2015). Intermittent Fasting and Human Metabolic Health. Journal of the Academy of Nutrition and Dietetics, 115(8), 1203–1212. doi:10.1016/j.jand.2015.02.018
- Ekmekcioglu C, Touitou Y. Chronobiological aspects of food intake and metabolism and their relevance on energy balance and weight regulation. Obesity Reviews. 2011;12:14–25