This summer was my second summer living in Istanbul during Ramadan, the holy month where Muslims fast from dawn until sunset. In hot summer months, this practice becomes especially taxing as the daylight period is significantly longer. Since Ramadan is a month long, people are still expected to go to work and maintain their normal responsibilities, all without any food or drinks to keep them energized throughout the day. A friend of mine who was fasting told me that he loses weight every Ramadan, but always gains it right back once Ramadan is over. Of course this is just one anecdote, but it made me curious about how fasting might impact health in the long term.
I was very happy to find that fasting was discussed in the August 2015 issue of Journal of the Academy of Nutrition and Dietetics article "Intermittent Fasting and Human Metabolic Health". The researchers were assessing the health outcomes of different fasting practices, specifically looking for changes in weight and metabolic parameters. The most interesting part of the article for me was the discussion of how fasting impacts different systems in our bodies.
Understanding how fasting could impact health is important for those who fast for religious purposes, as well as those who might try fasting as a method of achieving and maintaining a healthy weight.
Our entire circadian biology (the physical, mental, and behavioral changes in our bodies that respond to light and dark cues) could be impacted by fasting routines. You may be familiar with the human studies which show that people who have work shifts at night are at higher risk for poor health outcomes (obesity, diabetes, cardiovascular disease, and cancer). This is likely due to the changes in appetite regulating hormones that cause increased food intake. Also following this, studies have shown that consuming a greater amount of your daily calories earlier in the day is associated with better health outcomes (think: "breakfast like a king, lunch like a prince, dinner like a pauper").
Gut microbiota (the microorganisms living in our digestive tracts) may also be impacted by fasting. Our gastrointestinal systems are more active earlier in the day (greater blood flow and activity), and our metabolic rate is higher earlier in the day. A recent study showed that circadian rhythm disruption from jet lag was associated with growth of harmful bacteria in the intestines that are associated with obesity and glucose intolerance.
Impacts on sleep are important to consider for the fasting regimes that require night-time eating. Eating at night has been shown to reduce sleep quality, and reduced sleep quality is associated with insulin resistance. Despite what seems to be some discouraging evidence against fasting, intermittent fasting could potentially work for some people looking to control their weight. The simplest explanation for this is that it reduces the number of hours available for eating, so the overall energy intake may be lower. Also consider how overnight fasting is used in current medical practices before testing blood as it decreases the blood levels of biomarkers associated with chronic disease (i.e. insulin, glucose).
Research still needs to be done to show how fasting might be incorporated into a long-term healthy lifestyle for weight control. Currently, people are advised to avoid extreme hunger when they are trying to lose weight (frequent snacking is often recommended rather than a few large meals). Still, if periods of fasting do not lead to periods of overeating, periods of fasting may be a way to improve weight and metabolic health in the future.
One of my biggest questions and concerns would be about how to fit fasting into an active lifestyle. If fasting periods were to regularly interfere with physical activity, I would question the usefulness of them in the long term. I also wonder how short term fasting could help people to understand mindful or intuitive eating, as this seems like a place where those two could be brought together nicely.
What do you think about fasting and the impact it has on health? Have you fasted for religious/health/other purposes? Leave a comment!
Sources: Patterson, Ruth E. et al. (2015). Intermittent Fasting and Human Metabolic Health, Journal of the Academy of Nutrition and Dietetics, 115(8), 1203 - 1212.