At a time when our ancestors existed as hunter-gatherers in the Paleolithic, it's clear that food was not always available and that the fluctuation of feast and famine was probably more apparent. The theory of thrifty genes has it that our metabolic function is dependent on these fluctuations for optimal insulin function.
So, it's hypothesized that since intermittent fasting may have been instrumental in the selection of our genes, its practice may have lasting benefits on insulin sensitivity. Findings to date in humans are that fasting does improve insulin sensitivity by inducing increases in circulating adiponectin along with changes in plasma leptin. By these mechanisms, intermittent fasting acts on increasing insulin's action differently than physical activity.
Now, new research is showing that fasting one day each month may lower the risk of cardiovascular disease, according to research cardiologists from Salt Lake City. They observed 200 subjects, most being members of the Church of Jesus Christ of Latter-day Saints (LDS), whose monthly religious ritual involves fasting, or abstaining from two consecutive meals.
The study found that subjects who fasted regularly had a 58 percent reduction in risk of coronary artery disease. These findings may explain why Utah LDS routinely have lower risk of death from cardiovascular disease compared to other Utahns and the United States population.
The same research team conducted a smaller experiment observing metabolic markers on 30 subjects instructed to fast with water for 24 hours. The researchers observed increases in HDL and LDL cholesterol and found that human growth hormone (HGH) increased 20 times in men and 13 times in women. The surge of HGH stimulates fat burning as it prevents muscle breakdown.
When I asked Benjamin Horne, Ph.D., MPH, director of cardiovascular and genetic epidemiology at Intermountain Medical Center Heart Institute, and the study’s principal investigator, why the cholesterol numbers surged, he wrote me back, "This probably occurred because the body stopped metabolizing glucose and switched over to fat, which in order to obtain the fat to use as fuel the body would have scavenged fats from various places in the body where it stores such things during times of plenty, but especially the abdominal adipocytes.
"To extract fats from adipocytes, the body oxidizes the fat cells--or metabolizes them. When that happens, the fats in the adipocyte cells are dumped into the blood and circulated, and cholesterol molecules are some of those fats that would be extracted from the fat cells and put into circulation to be used as fuel (since no calories were being ingested during the fasting period)."
He presented April 3 at the American College of Cardiology's annual scientific sessions in New Orleans and confirms evidence from their larger 2007 study conducted on 448 Utahns (most of whom were LDS) published in the American Journal of Cardiology.
"These new findings demonstrate that our original discovery was not a chance event," Dr. Horne said.
The earlier study evaluated routine fasting among other LDS behaviors including social support, religious observance patterns, and abstinence from smoking, alcohol, tea, and coffee.
"Not only proscription of tobacco, but also routine periodic fasting was associated with lower risk of [cardiovascular disease]," Dr. Horne and his colleagues wrote. Routine periodic "fasting was also associated with lower diabetes prevalence."
The "likely explanation," they wrote, is that fasting influences metabolic health by assisting weight loss and improving insulin sensitivity through a "reset cellular sensitivity to glucose and/or insulin by periodically resting the system."
Finally, the authors point out that new findings suggest fasting also activates self-protective, cellular stress-resistance mechanisms (Sirt1, perhaps?).
Halberg, et al. Effect of intermittent fasting and refeeding on insulin action in men. J Appl Physiol 2005. Dec;99(6):2128-36. Epub 2005 Jul 28.
Intermountain Medical Center. Routine periodic fasting is good for your health, and your heart, study suggests. Science Daily 2011, May 20.
Horne BD, et al. Usefulness of routine periodic fasting to lower risk of coronary artery disease among patients undergoing coronary angiography. Am J Cardiol 2008.