Let's Talk About Intermittent Fasting

Intermittent fasting (IF) is a topic that I find fascinating. The more I read about it, the more I want to know.
Chances are that you have already heard about IF. The hype has been booming recently. But don’t think of it as a new "it" thing; in fact the first study on IF dates back to 1943.
The growing interest is due to new found evidence suggesting that IF can bring many health benefits, including a potential increase in human lifespan.


Definition

IF is an eating pattern that alternates periods of fasting and non-fasting.
The concept of IF has been made popular by Ori Hofmekler in his book called “Warrior Diet” and by Brad Pilon in his book called "Eat Stop Eat".
The main rationale behind IF is that

“Our ancestors consumed food much less frequently and often had to subsist on one large meal per day, and thus from an evolutionary perspective, human beings were adapted to intermittent feeding rather than to grazing1.”

How it works

There are no firm rules when it comes to IF.
However, two different approaches seem to prevail. The most “extreme” one being Alternate Day Fasting (ADF), which involves eating what you want one day, then a very restricted diet (fewer than 600 calories) the next day; without the need to keep an eye on what you eat on non-fast days.
A “milder” approach to IF is the one that involves a severe restriction on calories (between 75% and 90% of energy needs) on just 1 or 2 days a week. On the non-fasting day the individual is free to consume foods regularly and according to his/her liking.

Why is IF supposed to be good for us?

What happens during fasting periods is that when our bodies no longer have access to food they switch from "growth mode" to "repair mode".
In particular, the levels of the IGF-1 (insulin-like growth factor) hormone drop. As a consequence a number of repair genes appear to get switched on.
The IGF-1 hormone is one of the drivers which keep our bodies going, and cells reproducing and renewing themselves. IGF-1 is thus crucial when you’re growing (i.e., puberty) not so much afterwards².
It should be noted that the current medical opinion is that the benefits of fasting have not yet been tested in large human studies.
The largest evidence on the health and longevity benefits of IF has only been studied in shorter-lived mammals such as mice or invertebrates (i.e.,worms)3.
Some uncertainty remains as to whether IF increases longevity, as to the preferred method of practice, and whether it could produce harmful long-term health if done incorrectly.
However, a study published last year suggested (for the first time), that IF - when paired with calorie restriction - is an effective means of reducing body weight, fat mass, and visceral fat mass in obese women4.

Considerations

Here’s the “don’t this at home” warning. If you’re tempted to give IF a go, first of all gather as much information as possible.
Reading the two above mentioned books (Warrior Diet and Eat Stop Eat) can be a good starting point.If you’re really willing to embark on this "adventure", it’s also advisable to do it in a proper clinic or under medical supervision, because there are many people, such as pregnant women or diabetics on medication, for whom it could be dangerous.
To cite BBC’s journalist Michael Mosley:

“Fasting, like eating, is best done moderation5”

One last note. I've talked several times in the past about juice cleansing. It's something that I've done and that I will do from time to time. A juice cleanse is in fact a form of IF, in that for a couple of days you consume fewer than 700 calories. If you're tempted by IF you might want to test yourself with a juice cleanse and see how that goes.

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References
1 Mattson, M.P., PhD, Lancet 2005; 365:1978-80
2 http://www.ncbi.nlm.nih.gov/pubmed/21325617
3 http://www.fightaging.org/archives/2009/02/practicing-intermittent-fasting-versus-calorie-restriction.php
4 http://www.ncbi.nlm.nih.gov/pubmed/23171320
5 http://www.bbc.co.uk/news/health-19112549