Intermittent fasting (IF) has become a major trend in nutrition and with good reason. Martin et al’s 2006 review of IF and Trepanowski’s 2011 review both found numerous benefits in the literature; increased insulin sensitivity (decreasing type 2 diabetes), increased fatty acid mobilization (decreasing obesity), PPAR activation (a series of genes that regulate the expression of other genes- including genes for the liver, heart, kidney, muscle and adipose tissue), heat shock protein upregulation (improving cardiac protection), sirtuin upregulation (increasing telomere length), FoxO activation (kills tumors), increased BDNF (protecting against Alzheimer’s and Parkinson’s), upregulated cytokine function and many other benefits.
Clearly, for those who adopt a 14-18 hr fast and then have a calorically and nutritionally adequate eating window of 6-10 hrs can derive many benefits. Many users report that after adaptation, they have improved mood, concentration, sleep, physical stamina and other such n = 1 data points. With movements like crossfit and paleo nutrition endorsing IF, serious research is beginning to take a second look at it with a more penetrating look.
Recently, some research has emerged suggesting that women have poorer outcomes on IF. Martin et al 2008 revealed some very different results for IF using rats. Rats were placed on a 20% caloric restriction diet, a 40% caloric restriction diet, a 40% CR diet with IF, and a high fat/glucose diet.
The male rats on the CR and IF protocols developed the well-known benefits of these nutritional strategies. The female rats at 40% CR and 40% CR with IF however developed increased activity, increased cognitive function, decreased fat mass and (similarly to the males) but also lost fertility and demonstrated increased irritability.
Many women on IF protocols, once they have dropped below 18% bodyfat report trouble sleeping, poor cycle regulation, poor focus, increased irritability as well as many benefits. These of course are n = 1 cases with no controls and no one following exactly the same protocol, so while it makes for an interesting subset of data within a population, it does not allow one make conclusions.
Martin et al’s study actually raises the possibility that if women IF or CR too severely, while they may gain many health and longevity benefits, they may also rewire their hippocampus toward a chronically stressed state. While not chronic stress disorder or adrenal fatigue syndrome, this rewiring of the hippocampus can lead to both physiological and behavioral changes (as reported in the study). While IF and CR are both excellent tools, this second round of studies are needed to determine who can use what, when, for how long and why they should use it. Always listen to your own body.