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For most of recorded time, cultures around our planet and their wise traditions have recognized and honored the ritual of fasting. In addition, anthropologic studies of modern ancestral cultures like Hadza and Australian aborigines reveals periods of fasting and diminished caloric intake as a way of life, given seasonal variability and availability of plants and animals to consume.
Research studies in many life forms from yeast to primates have shown that caloric restriction of approximately 30% from baseline is associated with greater longevity. In addition, many lines of evidence in humans suggest periods of fasting to be associated with a “turning-on” or upregulation of deeply built-in resiliency systems. These include improved efficiency of metabolism, more effective sensitivity of insulin, more efficient cell recycling aka autophagy, more tolerant immune systems, i.e., less inflammation, and a host of other health-promoting metabolic changes.
The key concept of interest today is that of metabolic resiliency. This refers to our ability to efficiently burn our own fat when food is limited and to burn our fuel more cleanly, in other words, more energy produced with less free radicals and oxygen reactive species known to accelerate inflammation and aging.
What is confusing is that fasting can mean many different things. And while they all seem to offer many health benefits, they are not necessarily the same.
For example, here are some of the types of intermittent fasting (IF) that have (are being) been studied:
• The 5:2 IF: this is essentially ad lib intake 5 days/week with 2 days of caloric restriction in the 500-600 calorie/day range.
• The 16:8: this is time-restricted eating (TRE) where an individual consumes all their food in an 8-hour window, fasting for 16 hours. It is not intended to caloric-restrict. One eats what they want, just narrowing the window within which they consume. The smaller the window the better. Many reported health benefits including reduced risk of recurrence of breast cancer have been reported up to a 10-hour consumption window. While it is currently unproven, there may be a further advantage if the eating window is more closely aligned with sun-rising and sun-setting circadian cycles for that time of year.
• 24-hour IF: This is essentially fasting (water only) for 24 hours at specific interval e.g. monthly or every other month.
• Fasting-Mimicking Diet: This has been researched and popularized by Valter Luongo, PhD. It involves predominantly plant-based foods with caloric restriction of 500-600 calories/day for 5-straight days from monthly to every 2-3 months depending on one’s health goals.
I believe all of these strategies are substantial health-promoting upgrades compared to the “ad-lib” all day grazing most tend to do in modern life. Yes, this is a phenomenon of modern life!
Some of the above strategies, in particular the 16:8 or the 24-hour IF, will result in the liver’s production of ketones. Ketones themselves appear to have many unique health benefits from improved cell signaling, metabolism, epigenetic (how our genes can be turned on and off) effects and is a super fuel for the brain and heart. There may be important risk reduction of many chronic diseases like diabetes, neurological diseases, cancer, heart disease, etc. While the jury is still out on long-term risks and benefits of nutritional ketosis, the early returns are quite favorable.
Clinical trials of IF have been done in animals and humans. While most studies lump the above strategies, it is not clear if one has a great advantage over the other. I personally like the 16:8 and try to do it at least 2-3 days a week. Taking a whole-foods, minimally processed and nutrient-dense approach and then integrating it into one of the above strategies is a powerful 1-2 health promoting punch that will pay huge benefits!
These are some of the possible reported benefits from a review recently published in The New England Journal of Medicine (December 2019):
• Greater metabolic-stress resiliency at the level of cellular function in many different tissues
• Improvements in longevity and healthspan (quality of life)
• Improvements in sleep quality
• Reductions in obesity and diabetes risks
• Reduced cardiovascular risks
• Reduced cancer risks and enhanced recovery/prognosis with cancer treatment
• Improvements in neurodegenerative disorders like Parkinson’s, Alzheimer’s, ALS
• Improvements in inflammatory arthritis and asthma
• Improvements in wound healing and post-operative complications
As you can see, IF appears to have broad-based health promoting potential. While long-term clinical trials are limited, these strategies appear safe for most. While there will inevitably be a lot of pharmacological research to develop a drug that can “mimic” the effects of IF, they are likely to be inferior to the actual practice.
Dr. Mark Pettus currently serves as the Director of Medical Education, Wellness and Population Health at Berkshire Health Systems in western Massachusetts. In addition, he serves as The Associate Dean of Medical Education at The University of Massachusetts Medical School. He is the author of two books, The Savvy Patient: The Ultimate Advocate for Quality Health Care and It’s All in Your Head: Change Your Mind, Change Your Health. He serves on the teaching faculty at The Center for Mind-Body Medicine based in Washington D.C. and The Meditation Institute in Averill Park NY. He's also a member of NWI's Board of Directors.