Intermittent Fasting. What is it? Who is it for?
What is Intermittent Fasting?
Intermittent fasting has become very popular over the past couple of years for several reasons. It is free, simple, and seems to have great results. Perhaps, a more accurate name for this eating paradigm is time-restricted feeding. As there are several variations of time restricted feeding, not all of them putting someone in a ‘fasted state.’ What it comes down to, is restricting eating for certain time periods and then having all of your daily calories within a specific time span. There are many patterns which all fall under time-restricted eating.
Some popular eating patterns are:
- 16:8 - Which means 16 hours of fasting, 8 hours of eating. For example, eat your first meal at 10:00am and your last meal finishes at 6:00pm.
- Alternate-day fasting - Which is exactly what it sounds like. Eating for 1 day (usually 12 hours) then fasting the entire next day and night usually (36 hours).
- 5:2 - 5 days of eating unrestricted throughout the day and then 2 days a week, eating very little or fasting.
What are the Benefits of Fasting?
There are several health benefits for fasting. Some benefits explained in a 2019 New England Journal of Medicine article include: improved cognitive performance, decreased cardiovascular risk factors, increased physical performance, improved healing with tissue damage, encourages weight loss and can prevent and possibly reverse type two diabetes.1 These benefits come from both a caloric restriction, which is a side effect of eating in restricted windows, but also from hormonal and metabolic changes.1
Perhaps the most talked about benefit with time-restricted feeding is the promise of a longer life. Although not well studied in humans yet, fasting is linked to longevity in several animal studies.2 Research shows that restricting calories in animals, leads to increased life span when compared to regular feeding schedules.2
It’s hypothesized that this caloric limitation causes a type of stress on the body, leading to the development of adaptive mechanisms which in time make the body more resistant to disease and stress at a cellular level.3 Think about exercise as an example. Exercise is a type of ‘good’ stress that is put on our body. Although at the time of exercise, the body is under a great amount of stress, adaptions take place over repeated bouts of stress, leading to stronger muscles and improved cardiometabolic health.
Another aspect of time-restricted feeding is the process of autophagy which occurs in cells after fasting periods. Autophagy is the means in which the body ‘cleans up’ unwanted material and fixes damaged parts of cells.4 During autophagy, growth hormone is also produced. Increased autophagy is associated with both increased longevity as well as a decrease in chronic disease like Alzheimer’s and Parkinson’s disease as well as certain cancers.4 It is important to mention that inducing autophagy usually takes about 16 hours of fasting and becomes more efficient at the 24-hour mark.4 This amount of fasting may not be advised for everyone.
Who should avoid fasting?
Although fasting seems to be the perfect solution for many of today’s chronic diseases, it’s not for everyone.
Anyone who is currently or has struggled with eating disorders such as bulimia or anorexia in the past, is advised to not try out time-restricted feeding schedules. This restricted eating paradigm may lead to unsafe disordered eating patterns.
Pregnant and Nursing Women
Not only does restricting eating to certain windows make it more difficult to obtain adequate calories for a pregnant or nursing mother, but some studies have also found that fasting has been linked with lower birth weight in babies as well as premature labour.5
Although one of the most popular conditions that fasting is used for is diabetes, there are some very important points to address. Fasting is generally not recommended for patients with type 1 diabetes.6 Although some may be able to, they should discuss it with their healthcare provider and closely monitor blood sugar levels. People with type 2 diabetes may see great benefits with time-restricted feeding, however this should also be done under the supervision or a healthcare provider.
The young and the elderly
Just like any medical intervention, we must always be cautious with both the young and elderly. Time-restricted feeding is not recommended for children and teens as it may limit very important nutrients needed for growth and development. The elderly in general also struggle to meet basic nutritional demands and therefore fasting is not recommended for this age group as well.
This is not an exhaustive list of those who may see negative health impacts of fasting. Just like any health intervention, implementation must be individualistic. Perhaps a 16:8 fasting schedule is heathy for your body but a 5:2 schedule is not. Maybe you can go 36 hours without eating and notice higher energy levels while someone else may feel fatigued and irritable with fasting. So, if deciding to try out fasting, remember to seek advice from a regulated health professional and listen to your body.
1. de Cabo, R., & Mattson, M. P. (2019). Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine, 381(26), 2541-2551.
2. Mitchell, S. J., Bernier, M., Mattison, J. A., Aon, M. A., Kaiser, T. A., Anson, R. M., ... & de Cabo, R. (2019). Daily fasting improves health and survival in male mice independent of diet composition and calories. Cell metabolism, 29(1), 221-228.
3. Longo, V. D., & Mattson, M. P. (2014). Fasting: molecular mechanisms and clinical applications. Cell metabolism, 19(2), 181-192.
4. Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing research reviews, 47, 183-197.
5. Glazier, J. D., Hayes, D. J., Hussain, S., D’Souza, S. W., Whitcombe, J., Heazell, A. E., & Ashton, N. (2018). The effect of Ramadan fasting during pregnancy on perinatal outcomes: a systematic review and meta-analysis. BMC pregnancy and childbirth, 18(1), 421.
6. Kobeissy, A., Zantout, M. S., & Azar, S. T. (2008). Suggested insulin regimens for patients with type 1 diabetes mellitus who wish to fast during the month of Ramadan. Clinical therapeutics, 30(8), 1408-1415.