Since I’ve been fasting every other day to get rid of chronic inflammation in my knee, I’ve gotten a bunch of questions from friends about how alternate day fasting actually works, so here’s my best attempt to explain it without getting too technical and biological… If you do want all the biological nitty-gritty behind calorie restriction, here’s a link to a literature review done in 2003. Warning: It downloads a PDF.
Back in the day, some researcher was playing around with some mice, and discovered that if you restricted the amount of food that mice had access to by 20-30%, the mice would live significantly longer, would have much better health, sleeker coats, and wouldn’t develop degenerative diseases like diabetes. The same effect was then proven in all sorts of other species like monkeys (closer to humans), and yeast (easier to do genetic studies on).
Many years later, after genomic research became possible, it was identified that the when you restricted calories one of the effects that happened was that a certain gene (called SIRT1 in humans) was activated. This gene then had many effects downstream, causing repair mechanisms to go into overdrive, and reducing damaging processes such as inflammation and other degeneration, leading to the increases in health and lifespan.
Then the question became why restricting calories leads to such an effect. Essentially, humans evolved as hunter-gatherers in Africa, and life as a hunter-gatherer, while actually pretty easy, did include periods of famine and involuntary calorie restriction. When there wasn’t enough to eat, the human body developed mechanisms to direct all the energy of the body towards repair and preservation of the body, so that the moment food did become available again, the individual was fit and ready to go out and get it. During calorie restriction the body also down regulates any processes that are causing low level chronic problems, and furthermore, the lack of food reduces the oxidative stress on the organism as a whole (oxidative stress is the production of free-radicals that is inherent in metabolism – lower metabolism equals less oxidative stress).
After all this evidence started being reported, there were some intrepid souls that undertook to attempt calorie restriction on themselves for the life-extension and health benefits. I imagine that it was extremely difficult – can you imagine being hungry ALL the time. Furthermore, such people were often derided as simply trying to justify and promote eating disorders, which in at least a fraction of cases was probably true.
So, to bring this back to me and my knee, the important part of the whole puzzle was that relatively recently people began studying intermittent calorie restriction, and they discovered that restricting calories temporarily had pretty much the same effects as a permanent restriction. Due to the lag inherent in body processes, the pulses of SIRT1 activity that come from fasting every other day are sufficient to lead to the same repair, anti-inflammatory, and life extension benefits that permanent calorie restriction does.
And very importantly, alternate day fasting is much easier to do than permanent calorie restriction, even if only for a month at a time, making it possible for me to do this and still function reasonably.
If you want more information on the specifics of the application of alternate day fasting to inflammation, here’s a good summary of a paper linking alternate day fasting to increases in SIRT1, and then another summary of a paper describing how SIRT1 blocks inflammation.
