Studies have shown that calorie-restricted diets offer beneficial effects on health and longevity across a broad range of species. Nonetheless, for humans, constantly restricting daily food intake can be extremely difficult.
Fortunately, it turns out that short-term or intermittent fasting may provide the same health benefits without having to overcome constant, daily hunger pangs.
The Health Benefits
Experimental studies are only beginning to highlight the health benefits of intermittent fasting.
Good Housekeeping: Fasting promotes a form of “cellular housekeeping” called autophagy. Autophagy is a process by which the body removes the damaged and defective parts of a cell. “By fasting, what you are in effect doing, is marshalling all of the body’s energy (much of which would normally go into digesting) and focusing it on whatever needs to be cleaned or repaired, “said Paul Bragg, author of The Miracle Of Fasting.
Cancer: Cell proliferation (the rapid multiplication of cells) plays an important role in cancer formation. For this reason, many studies looking to evaluate the effect of dietary interventions on cancer risk use cell proliferation rates as a tool to measure effectiveness. Findings from animal studies indicate that alternate-day fasting may reduce cancer risk by reducing cell proliferation (1).
Longevity: Study after study has indicated that intermittent fasting may be associated with increased lifespan in animals (2, 3). Doctor Valter Longo, director of the University of Southern California’s Longevity institute, has conducted research showing that intermittent fasting decreases the expression of insulin-like growth factor 1 (IGF-1). IGF-1 plays an important part in metabolism, growth and development. Reduction in IGF-1, brought about by intermittent fasting, is thought to play a key role in slowing the aging process.
Brain Health: Fasting may promote brain health. Studies on mice have shown that intermittent fasting may improve brain function by reducing oxidative stress (4). Oxidative stress is associated with aging of the brain. It can injure cells as well as impair learning and memory. Conditions tied to oxidative stress include Parkinson’s disease and Alzheimer’s disease.
Heart Disease: Intermittent fasting has been shown to reduce several indicators of cardiovascular disease by lowering triglycerides (a type of fat found in the blood), low-density lipoprotein (bad cholesterol) and blood pressure (8). Research points out that it is not absolutely clear whether these heart protecting benefits are simply due to weight loss, and possibly not the act of fasting itself, but since weight loss and short term fasting appear to go hand-in-hand it’s a win-win.
We’ve all heard it; stop eating for a couple of hours and your body will enter starvation mode, hording fat and drastically slowing your metabolism. But conventional nutrition knowledge doesn’t always hold up, and this appears to be one of those instances.
Research shows that metabolic rate actually increases during periods of intermittent fasting (5). However, there is some truth to the “starvation mode” theory. Prolonged fasting (longer than 4 days, although this may vary) does eventually result in decreased metabolic rate.
Weight loss and Fitness
A faster metabolism isn’t the only upside to short term fasting. Human studies report increases in fat oxidation leading to fat loss in non-obese individuals (6) and show alternate-day fasting to be an effective diet strategy for obese individuals wanting to lose weight (7).
The proposed weight lowering mechanism is due to the body’s ability to use fat as a fuel source. When you stop eating, the first thing your body will do is utilize the glucose floating around in your blood for energy. Next, your body will convert glycogen (stored in the liver and muscle cells) into glucose. After 6 to 8 hours, when glycogen stores have been depleted, your body will shift into fat burning mode (queue Survivor’s “Eye Of The Tiger) and burn stored fat to use for fuel.
In much the same way, exercising coupled with fasting may be very useful for anybody looking to loose a bit of weight. In his e-book, Eat Stop Eat, fitness expert Brad Pilon explains, “Athletes performing long endurance activities while fasting actually burn more body fat than athletes who are fed (because the fed athletes are burning through food energy before they get to the stored energy in their body fat)”.
How to Short Term Fast
Intermittent fasting involves periods of avoiding food followed by periods of regular eating. This way of eating mimics the eating patterns required of our hunter-gatherer ancestors-when food was not always readily available. According to Mark P. Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging in Baltimore, “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 grazing”.
There are a number of ways to coordinate a short term fast. One way is to fast for 14 to 16 hours. Although fasting hours are chosen by individual preference, an example would be to eat only between the hours of 1pm to 9pm. Another approach is to fast for 24 hours. This schedule stills allows eating everyday, such as a 24 hour lunch-to-lunch or dinner-to-dinner fast. Alternate-day fasting, where fasting takes place every other day, is commonly used in research studies. Others choose to fast “organically”, meaning if you wake up in the morning and you aren’t hungry, skip breakfast and don’t eat until you are.
Listen to Your Body
Overall, fasting seems to provide numerous preventative and restorative functions that contribute to good health. If you are already living a healthy lifestyle, healthy fasting may be something interesting to try.
Remember, fasting may not be for everyone. Like with any dietary change, listen to your body and monitor how you feel. If it doesn’t feel right, don’t push yourself. If you are pregnant or nursing, diabetic, or suffer from a mental disorder, fasting is not recommended.
- Hsieh EA, Chai CM, Hellerstein MK. Effects of caloric restriction on cell proliferation in several tissues in mice: role of intermittent feeding. American Journal of Physiology – Endocrinology and Metabolism 2005; Vol. 288 E965-E972
- Goodrick CL, Ingram DK, Reynolds MA, Freeman JR, and Cider NL. Differential Effects of Intermittent Feeding and Voluntary Exercise on Body Weight and Lifespan in Adult Rats. J Gerontol 1983; 38 (1): 36-45
- Sogawa H, Kubo C. Influence of short-term repeated fasting on the longevity of female (NZB x NZW) F1 mice. Mechanisms of Ageing and Development 2000; 115:61-71.
- Li L, Wang Z, Zuo Z. Chronic Intermittent Fasting Improves Cognitive Functions and Brain Structures in Mice. PLoS ONE 2013; 8(6): e66069. doi:10.1371/journal.pone.0066069
- Mansell PI, Fellows IW, Macdonald IA. Enhanced thermogenic response to epinephrine after 48-h starvation in humans. Am J Physiol. 1990;258(1 Pt 2):R87-93.
- Heilbronn LK, Smith SR, Martin CK, Anton SD, Ravussin E. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Am J Clin Nutr January 2005; vol. 81 no. 1 69-73
- Varady KA, Bhutani S, Church EC, Klempel MC. Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr November 2009; vol. 90 no. 5 1138-1143
Varady KA, Bhutani S, Klempel MC, Lamarche B. Improvements in LDL particle size and distribution by short-term alternate day modified fasting in obese adults. Br J Nutr. 2011 Feb;105(4):580-3.