Reading through the literature, it was interesting to discover that while most of the buzz surrounding intermittent fasting (IF) is a relatively new phenomena, the first documented study on the effects of IF on longevity was published in 1945.  In fact, this study includes references to previously conducted research dating back to 1887 which examined the nutritional effects of IF on chickens (though not longevity).  For those of you that can’t sleep at night, the full text of the 1945 study is available for free online, you can find it here.


This study, like nearly all that I’ve found thus far examining the effects of IF, subjects rats to a protocol of eating either 1 day in 2, 1 day in 3 or 1 day in 4.  Their diets varied, but protein consumption ranged from 30 to 35% with most other calories coming from carbohydrates.  In total 137 rats were studied with 33 in the control group, 37 in the 1 in 4 day fasted group, 37 in the 1 in 3 day fasted group and 30 in the 1 in 2 fasted day group.  Interestingly enough one of the authors also subjected himself to both the 1 in 2 and 1 in 3 day protocols.


Below are some of the important things I took away from the study:

  1. The lifespan of the male rats improved more than that of the females.  The average fasted male saw a 9% increase in lifespan over their control group while the average fasted female saw a 6% increase.
  2. For males the 1 in 2 day fasting was most beneficial while for females 1 in 3 day fasting provided the greatest increase in lifespan.
  3. Something about the rat’s digestion system substantially affected the results.  Though the average lifespan increased for all but one of the intermittently fasted groups, the standard deviation was much greater than that of the control group.  Basically, most of the control rats died within a similar time range, while those on the IF protocol exhibited a wide range of lifespans – including early deaths.  The authors attribute this effect to the nature of the rat’s digestive system (which is dissimilar to that of humans).


There have been a number of more recent studies that support the findings in this study, though I have yet to find the full text for any of these articles freely available online – if I do, I’ll be sure to come back and update this page.


So do the findings in the outlined research demonstrate that if you follow an intermittent fasting protocol of fast for 16 hours, feed for 8 (as I have done) that you will live a longer life?  Nope.  Why not?  Well, first, the durations of fasting and feeding for the rats is different (1 in 2 days being the shortest) and even if they were the same they don’t serve as a one-to-one example.  While rats do mostly adhere to the 24 hour daily cycle that humans do, their lifespans are much shorter (1 day is a lot longer in proportion to their life than it is to a human’s).  With that said, there is a substantial body of evidence that feeding and fasting improves longevity.  We simply do not fully understand the mechanisms yet.  The research in this area is ongoing and hopefully we will start to characterize the processes that fasting induces or improves within the body to increase lifespan.  Until that time though, there are numerous other reasons to adhere to intermittent fasting which, I’ve mentioned at a cursory level, but will dive deeper into in future posts.


If you’re aware of research in this area that I haven’t mentioned, please feel free to let me know about it in the comments.