One of the most controversial aspects of nutrition is the practice of not eating, at least for a limited or moderate amount of time. While this has served our species well over the course of evolution, it has always been enforced by seasonal or environmental pressures causing limited food availability and, until more recently, has rarely been self-imposed. In addition to those benefits observed in humans, improvements in the health of all mammals ever studied have also been observed. Limited fasting provides the body with an improved immune function, an ability to discard the metabolic clutter that is hindering cellular function, and ways to recycle those aspects of our metabolic hardware that need to be replaced. These processes require a shortage of calories, carbohydrates, and/or protein to be switched into the “on” position and if we are constantly in a “fed” state we miss out on one of the true physiological feats of evolution.
Of course there are limits to these restrictions and we have to stay nourished, receiving adequate protein to maintain muscle mass, healthy fats for brain health, and the micronutrients (vitamins and minerals) to preserve organ reserve are essential. However, recent investigations have shown that too many Americans are both overfed and malnourished. Most people eat over 15 hours or more per day! A large amount of the food consumed over this window of time could be categorized as largely filler-type quality. Flour-based baked goods, sweetened foods, fruit juice, and those foods containing large amounts of industrial seed oils represent more than 75% of the calories consumed during the average American’s day.
While there are numerous issues at hand with these food choices, it may be even more damaging to our health to eat these foods over such a large daily time period. In essence we are always in a fed state and that’s just not normal for humans, whose metabolism and capacity to safely digest, absorb, and process nutrients has been shaped by thousands of years of somewhat limited access to food. The various organs involved in metabolism never truly shut down and asking them to work nearly around the clock takes its toll.
Made popular recently by several different types of highly publicized limited-fasting plans, researchers are making an effort to better understand the process responsible for the improvements in health observed. However, there isn’t a one-size-fits-all duration or frequency of fasting. There are various approaches that utilize a wide variety of food restriction which have proven effective. For those who previously failed to feel better or lose weight with the general “less of everything, and everything in moderation” approach, any one of the 13 to 16- hour, limited fasts often prove to be the real difference maker. Research is very supportive of overall benefits (1,2). No negative effects have been observed in animals or humans, so long as the restrictions are not carried out too far and not attempted during specific phases of the life cycle (not a great idea for young children, for instance).
Staying metabolically flexible is a great benefit of modest time restricted feeding. If carbohydrates are always available as a fuel, we will never generate and ultimately offer our central nervous system anything else as a source of energy. With restrictions however, ketones or fats become the primary energy sources. This shift alone carries immense long-term benefits to the brain and beyond. In contrast, always being “well fed” and/or satiated creates storms on the endocrine, cardiovascular, and neurological fronts.
It is an approach to be considered. More and more individuals are using this as a viable tool to improve mental clarity, beat a difficult infection, or reverse insulin resistance. Increasing the window of time without eating significant amounts of protein or carbohydrate can be a very healthy and effective means of supporting our innate, metabolic, detox efforts. However, recent research at the SALK Institute in Southern California, led by a circadian-entrainment expert, Dr. Satchin Panda PhD, showed that restricting food intake to a 10-hour window, regardless of the diet’s composition, proved immensely beneficial to the individuals in that arm of the study (3).
Researchers believe that the primary role of our circadian clock has more to do with metabolism than any other aspect of our life. The internal timing is essential to balance adequate nourishment and necessary physiological repair during fasting. When our circadian clock is disrupted, as when humans do shift work, the balance between nourishment and repair breaks down and diseases set in. Unfavorable gene expression may also be a very important aspect of is relation to various disease processes.
A process known as autophagy is related of this. The ability of a cell to initiate its own digestion of defective mitochondria and other cellular organelles is often the only way we can eradicate some types of infections. The herpes virus for instance, carried by over half of humans and responsible for everything from cold sores to serious neurological complications, has the unique ability to hide in our cells and keep normal defense systems turned off. So much ahead of our own evolution, this virus is often undetected. Even when it is detected it cannot be eradicated with normal immune-triggered autophagy or apoptosis. In cases like this, and there are numerous other ones, only an extended window of fasting (typically 16+ hours) provides the environmental stimuli for this internal “house cleaning”. Eliminating damaged and underperforming mitochondria, recognizing mutated DNA, and initiating the destruction of infected cells are important processes required to stay healthy and to age well.
If macronutrient restrictions are considered as part of the approach then it is important to consider that fat is the most forgiving source of energy when it comes to enabling “fasting” benefits even in the absence of a true fast. The source of that fast is critical though. Staying with predominantly saturated or monounsaturated fats like those found in extra virgin coconut oil, grass-fed butter, macadamia nuts, extra virgin olive oil and avocados are the best choices. At a time when carbohydrate restrictions are most popular, limiting protein is also essential for enhanced autophagy.
The research surrounding this topic is fascinating and empowering. In addition it should make us ask important questions regarding our approach to health and solutions for supporting those with critical conditions. For those that require enteral nutrition as example, the evidence would suggest that continual feedings may have significant downsides and that tube feedings should also be limited to windows of time as tolerated. While there are always a large number of variables that need to be considered for every patient, each with their own influence on the disease or condition, certainly there are many cases where considering this science makes sense.
~ John Bagnulo MPH, PhD.
1. Wegman MP et al. Practicality of intermittent fasting in humans and its effect on oxidative stress and genes related to aging and metabolism. Rejuvenation Res. 2015 Apr;18(2):162-72.
2. Tinsley GM and LaBounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661-74.
3. Amandine Chaix, Terry Lin, Hiep D. Le, Max W. Chang, Satchidananda Panda. Time-Restricted Feeding Prevents Obesity and Metabolic Syndrome in Mice Lacking a Circadian Clock. Cell Metabolism, 2018; DOI: 10.1016/j.cmet.2018.08.004