Intermittent Fasting: Revisited

Intermittent Fasting: Revisited

Intermittent Fasting is arguably one of the biggest health trends in recent years and has been associated with numerous related benefits.  I wrote about this topic over a year ago (check my original blog here) and thought now would be a great opportunity to revisit the subject and comment on some of the latest literature on this nutritional timing phenomenon.

To refresh, what is intermittent fasting?

Most people use Intermittent Fasting as a catch term to explain numerous methods of fasting, some technical terms for fasting protocols include: Time Restricted Feeding (the trend most people are on), alternate day fasting and religious fasting (Ex. Ramadan).  Using a broad definition, Intermittent Fasting is a nutrition timing concept that focuses on eating all food within certain hours of a standard 24 hour cycle with fluid intake being determined by the type of fast (Ex. Ramadan vs Time Restricted Feeding).

How does Intermittent Fasting work?

A concept our bodies have honed over millions of years of evolution is homeostasis — the desire to maintain a functional balance between all interacting elements.  This can also be thought of as regularity, and that is precisely how Intermittent Fasting is thought to act through, setting and firming metabolic regularity.  This metabolic regularity seems to directly impact our circadian biology, our microbiome and modifiable lifestyle factors which are positively impacting our health.

Circadian Biology: We as humans as well as other organisms have learned over the years that there are optimal times for specific physiological processes to occur, therefore, it was evolutionary advantageous for us to have our own (endogenous) biological clock to keep track of everything. This is known as our circadian rhythm.  Circadian rhythm plays a critical role in metabolism, hormone secretion patterns, sleep and even physical coordination, disruptions in this rhythm have a systemic negative impact on the processes just previously mentioned. Our master biological clock (located in the hypothalamus) is cued by light-and-dark stimuli.  We have additional biological clocks located the in the peripheral areas of the body (Liver, fat cells, muscle cells) which are cued by other signals including movement and feeding.  It seems that feeding signals are the dominant regulators for our peripheral clocks. When we have desynchronization of either our master clock or peripheral clocks, we increase the risk of chronic diseases. Intermittent Fasting helps keep our internal clock(s) in sync by minimizing de-synchronization triggers like feeding signals.

Gut Microbiome: As mentioned, our bodies runs on a circadian rhythm and our gastrointestinal tract (gut) and its functions, as part of our bodies, are regulated or influenced by the oscillation of waking and sleeping.  A couple of examples include: increased blood flow during the day compared to night, emptying of stomach contents is greater during the day than at night and we respond slower to glucose (sugar) during the evening compared to during the day.  As part of fasting protocol, an individual typically increases the amount of time (in hours) where they do not consume food, this allows the gut to take a break from digestion and shift its focus to other priorities like gut proliferation (new bacteria), intestinal wall repair, etc.  These other priorities if completed, have been shown to help with digestion, obesity and other chronic diseases. Essentially with Intermittent Fasting we are trying to ensure all food is eaten within a certain time frame and that time frame should coincide with when our body is best able to metabolize our food and still provide enough time for gut rest & repair.

Modifiable lifestyle factors: Fasting protocols seem to have the ability to impact modifiable lifestyle factors such as energy intake, sleep, and weight.  The scientific research on this is certainly lacking; however, the small research that has been completed seems to be positive.  For energy intake specifically, individuals who either restrict calories as part of their fast OR increase fasting hours tend to have lower energy intakes over the subsequent days which can lead to weight loss and improvements in various biomarkers. Night time eating is one of the biggest contributors to diabetic risk,  obesity, and impacts both sleep duration and quality.   Feeding signals at inappropriate times (late night eating) causes a de-synchronization of our circadian rhythm which directly impacts our normal sleeping patterns. Intermittent Fasting protocols have been shown to have a significant positive impact on both sleep duration and sleep quality by eliminating inappropriate feeding signals.

Take home:

  • Intermittent fasting helps the body establish and set metabolic regularity.
  • Eating within a certain window of time (Intermittent fasting) ensures our body is able to metabolize the food we eat in an efficient manner and allow for gut rest.
  • When we send feeding signals at inappropriate times (Late night eating) we cause a desynchronization of our circadian rhythm and increases our risk of developing chronic diseases.
  • Common Fasting protocols include:
    • 14:10 (14 hour fasting: 10 hour eating); ex. 9 am – 7 pm eating window
    • 16:8 (16 hour fasting: 8 hour eating); ex. 12 pm – 8 pm eating window (What I personally do!!)

Patterson, R. E., & Sears, D. D. (2017). Metabolic effects of intermittent fasting. Annual review of nutrition, 37, 371-393

Anthony Barsby

As our Human Performance Specialist, Anthony provides clients with comprehensive and customized lifestyle coaching through face-to-face consultations and online mentoring. A Certified Exercise Physiologist, Anthony administers fitness assessments and designs exercise programs that address each individual's goals and needs.