Intermittent fasting (IF) is currently one of the biggest health trends worldwide, with many claims that it is the key to losing weight, reducing inflammation, and promoting health.
What is it?
IF is characterised by alternating periods of normal eating with periods of total food absence, the most popular method involving restricting the daily eating period to 8 hours of the day (e.g. between 12pm and 8pm), and fasting for the remaining 16 hours. Other methods include fasting for a full day for one day of the week, or eating a very small amount of food (e.g. 500 calories) on two days of the week, and eating normally on the other 5 days.
During the fasting period, plain water can be consumed, as well other zero-calorie beverages like black coffee and tea. Some methods also allow other items such as bone broth and apple cider vinegar.
How it works
When we eat, the body breaks down food into molecules which travel through the blood stream and are used by our cells for energy. If our cells don’t use it all, our insulin levels rise, and the excess energy is stored in the cells as fat. In between meals, given we don’t eat for a while, this stored energy is released and used by the body.
The idea behind intermittent fasting is that during periods of prolonged fasting, our insulin levels remain low for longer periods of time, and the energy stored within the fat cells can be burned off. Note that what is eaten during the non-fasting period must still create a calorie deficit in order to cause weight loss. You can still gain weight while doing IF if you are consuming too many calories overall. It seems however that generally speaking, eating fewer meals with IF leads to an automatic reduction in calories.
Intermittent fasting has not yet been shown to be more clinically effective than calorie restriction when it comes to weight loss; both are just different methods to creating an energy deficit.
However, research suggests that there may be several benefits of fasting apart from just weight loss. This is due to the changes and processes that occur within the body on a molecular level during extended periods of fasting. This includes an increase in cell regeneration, decreased inflammation and removal of oxidative stress within the body, which ultimately can have effects on longevity and delayed onset of disease. In a day in age where 3 main meals and snacks in between is emphasised, these processes do not occur nearly as often as the body rarely goes for long periods without food. Fasting also appears to have a positive impact on blood sugar regulation, as well as cholesterol and triglyceride levels.
More studies are required to better understand the effects of intermittent fasting on the body. These kinds of dietary patters may not be recommended for some athletes as it may impact performance – particularly when training may fall within the fasting period. It also is not recommended for women who are pregnant or breastfeeding, individuals who are underweight or suffering from an eating disorder. Speak to a dietitian to see if IF could be beneficial for you.
De Cabo, R., Mattson, M.P. (2019). Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med 2019; 381:2541-255. DOI: 10.1056/NEJMra1905136
Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients, 11(10), 2442. https://doi.org/10.3390/nu11102442
Stockman, M. C., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent Fasting: Is the Wait Worth the Weight?. Current obesity reports, 7(2), 172–185. https://doi.org/10.1007/s13679-018-0308-9