Thursday, September 12, 2013

The benefits of Intermittent Fasting - a Mamamia blog for adults

With the Jewish fast of Yom Kippur approaching, I have been thinking about the biological value of fasting.  Fasting is fairly common among the major religions of the world. Muslims observe a month of fasting during Ramadan. Jews have seven major fast days and three minor fasts. Hindus fast during New Moon Days in festival periods. The Greek Orthodox observe three sustained periods of dietary restrictions. The religious motivations for the fasts are variable but all spiritual in nature, including atonement, purification, increased prayer focus. Although fasting is gaining popularity for dieting purposes, I was curious about the wider health benefits of intermittent fasting.

I began thinking about this after reading a recent study conducted in a Muslim population observing Ramadan. The researchers collected subjects' blood before, during and after Ramadan. Their findings indicate that during fasts inflammatory hormones are lower than during periods of normal caloric intake. There are 2 aspects to this study that are interesting. One, it adds to our understanding of why intermittent fasting or caloric restriction might be beneficial.  Two, it compared fasters to themselves in a 'real-world' setting.  Individuals observing Ramadan were observing a short term fast between 13-18 hours long followed by a feast. Despite how short the fast was and that it was followed by a large caloric intake, the fasters still had significantly lower circulating inflammation markers.

Rarely do religions promote intermittent fasting because it is good for your health; but it turns out intermittent fasting is very healthy for today's developed populations. Just as Lent and the laws dictating Kashrut have health benefits or did at the time of their inception, fasting may be valuable with our increasingly sedentary lifestyles.

Many studies, in addition to the Ramadan study, have demonstrated the health benefits of intermittent fasting, such as:
lower glucose and insulin levels
decreased inflammatory response
reduced markers of oxidative stress
increased insulin sensitivity
decreased blood pressure 

Sustained periods of intermittent fasting, when subjects fast every 2nd or 3rd day for 2-10 weeks, has dramatic effects on morbidity and indicators of chronic disease, such as:
reduced vascular disease risk
decreased BMI
slowed cancer cell growth
reduced chemotherapy side effects

How? There are many theories on why intermittent fasting may be beneficial.  The most popular theory suggests intermittent fasting drops circulating blood glucose levels which initiates a cascade of beneficial effects. For example, sustained low blood glucose levels reduces circulating insulin, which then leads to a reduction in other hormones, including inflammatory promoters.

Why? Modern humans are believed to have been genetically selected for primarily during times when we coped with periods of feast alternating with periods of famine.  It may be that because this is the environment we were selected for our bodies are not actually meant to have sustained caloric intakes of 2000 kcal and above.

When?  Intermittent fasts should be just that intermittent. Most studies have looked at fasting that lasts between 15-20 hours and occur as often as 3-4/week.  However, studies analyzing less frequent fasts (i.e. once/week) see a lot of the same benefits.  However, the research has been done on healthy, non-pregnant adults that are drinking water during the fasts.

Whether it is for spiritual reasons or not it, it seems occasional fasting does the body good.
Food for thought......

Some insightful sources:

Faris, et al. Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects. Nutrition Research, 2012 (32).

Bartke, et al. Effects of dietary restriction on the expression of insulin-signaling related genes in long-lived mutant mice. Interdisciplinary Top Gerontology, 2007 (35).

Varady, et al. Alternate-day fasting and chronic disease prevention: a review of human and animal trials. American Journal of Clinical Nutrition, 2007 (86).

Trepanowski, et al. Impact of caloric and dietary restriction regimens on markers of health and longevity in humans and animals: a summary of available findings. Nutrition Journal, 2011 (10).


  1. Mamamia--So this type of fasting is only beneficial above and beyond the sleep-fasting we all do every night right?

    1. Sleep-fasting is clearly not healthy, despite its popularity. :)