The 411 on Fasting
Not all things that go mainstream are necessarily bad or fads. This is where we need to slow down our knee jerk reactions and fully grasp what we are assessing. Fasting is something that falls into that category very well. When you think about it it’s actually pretty silly to call fasting a fad. Fasting has been around for a long time…no I really mean a LOOONG time, like ancient Greece and Old Testament long.1 So the idea that it’s purely a weight loss fad is just uneducated and silly.
Now again the nuance is that there is no one size fits all and fasting is not necessarily something that needs to happen every day for every person in the same way at the same time. This phenomenon I would agree is a modern construct where someone is trying to cash in on a popular trend and promising you the stars. Fasting is not magic. It is biology. Plain and complex biology. So for all of the family members or health gurus who have told you fasting is a dangerous or unhealthy fad, let’s dispassionately look at the biochemistry of fasting from a high level and put this to rest shall we…
A typical range for intermittent fasting is anywhere from 16-48hrs. It is truly a backwards way of thinking that fasting is the fad and eating 3 meals per day plus snacks is remotely evolutionarily consistent. This denies human adaptation to feast/famine cycles and generally sporadic eating patterns over millions of years of human evolution. In fact it was this evolutionary pressure placed on humans by food scarcity that selected for those whose cognitive capacity was heightened during these periods of food depravation. There are adaptive responses to the neuronal network in the face of food deprivation. The obvious switch from glucose utilization to fatty acids and ketone bodies is one of the significant metabolic switches that occur but in addition to providing substrate for mitochondrial ATP(energy) production, ketones also activate signaling pathways involved in synaptic plasticity and cellular stress resistance.2
One specific neurotrophic factor, BDNF (brain-derived neurotrophic factor), plays a critical role in learning, memory, synaptic plasticity, hippocampal neurogenesis, and enhances neuronal stress resistance. In fact both fasting and running enhance spatial learning and memory along with BDNF. This is why I love fasted training. However this upregulation in neuronal network activity during food seeking behavior(decision making, navigation etc…) also increases mitochondrial function, antioxidant defenses, DNA repair and inflammation supression.2 So again these adaptive changes both enhance cognition and increase the resistance of the brain to injury and disease. Does all of this sound like a fad still?
On the flip side, excessive food intake in animal experiments and human modern culture actually impairs neuroplasticity. Chronic food consumption results in little to no metabolic switching which can lead to a lessening of neuronal engagement and eventually insulin resistance. So these signaling pathways in the brain become disengaged and the results are suboptimal cognition, vulnerabilities of the brain to stress and neurodegenerative disorders.2 Specifically Alzheimer’s disease and Parkinson’s disease have been seen in animal research with high energy intake and diabetes.
I could go on and on with the biochemistry all day long but the larger more actionable point to consider is that our current food environment is new…in fact I would argue THIS is the fad and it is THIS that needs to change. I think of fasting as a tool to mimic a more evolutionary consistent time that seems far better suited to our biology than chronic food consumption. Now all this being said, once pathology has taken over, fasting may become much more difficult and complicated. But this should not be the rule. Sadly in our society sickness and disease has become the rule today as only roughly 12% of Americans can be considered metabolically healthy.3 This is unsustainable.
So my call to action is simple. Find a way to incorporate some degree of time away from food into your life. Again this would be in accordance with your goals, current metabolic situation and life circumstances(ie pregnancy). This is not only about weight loss. In fact even absent weight loss fasting may improve blood pressure, lipid and glucose metabolism.4 Not magic, biology! Most people don’t realize that they already do some form of fasting while they sleep. It’s not uncommon for people to realize when they do the math, that they already are somewhere between 10-12hrs fasted per day. At that point it becomes a psychological game with yourself. Do you really think another 4 hours without food will kill you? Certainly the answer is no. We would not be here as a species if that were the case. This underlies the programming we have surrounding food. Fasting was once a normal part of human existence. Now it is considered a fad? I think the food industry would LOVE for you to think of fasting as a silly fad. The biology tells us otherwise and in my opinion we would be wise to create space away from food in our lives.
There are so many ways you can fast. Don’t get caught up in rules and dogma. Just find what works for you and experiment. Nobody knows your body better than you and I assure you, your body and your brain will thank you!
1. Kerndt PR, Naughton JL, Driscoll CE, Loxterkamp DA. Fasting: the history, pathophysiology and complications. West J Med. 1982;137(5):379-399.
2. Mattson MP. An Evolutionary Perspective on Why Food Overconsumption Impairs Cognition. Trends Cogn Sci. 2019;23(3):200-212. doi:10.1016/j.tics.2019.01.003
3. Araújo J, Cai J, Stevens J. Prevalence of Optimal Metabolic Health in American Adults: National Health and Nutrition Examination Survey 2009-2016. Metab Syndr Relat Disord. 2019;17(1):46-52. doi:10.1089/met.2018.0105
4. Zhu S, Surampudi P, Rosharavan B, Chondronikola M. Intermittent fasting as a nutrition approach against obesity and metabolic disease. Curr Opin Clin Nutr Metab Care. 2020;23(6):387-394. doi:10.1097/MCO.0000000000000694