Over the last decade, I have fasted a lot, and presumably much more than I should have. In total, I have done about fifty or so 36–48-hour fasts, about ten or so 5-day fasting-mimicking fasts (eating about 500kcal per day in the form of vegetables and unsweetened nut butter), and one 9-day-only water fast.
I did this on the premise that fasting is one of the most potent health interventions out there. Fasting increases autophagy, reduces mTOR activation, and promotes mitochondrial recycling. Through these and other mechanisms, it is thought to rejuvenate the immune system, to increase organ health (perhaps in part by the elimination of senescent cells), and to protect against diabetes, cancer, and cardiovascular diseases.
When I fasted for multiple days, I never did complete water-only fasting but rather so-called “modified fasting”. I usually ate one or two spoons of peanut or almond butter a couple of times per day and occasionally some mushrooms, spinach, sauerkraut, or other ultra-low caloric and glycemic foods.
Most of the benefits of fasting (other than weight loss) are probably due to getting levels of insulin and some amino acids (leucine & methionine) to as low as possible for a longer period of time. When insulin and dietary protein intake are kept very low, mTOR activity drops, which, among many other things triggers autophagy.
Thus, eating foods that have a low glycemic index (cause little insulin secretion) and have little protein (have little methionine, leucine, and isoleucine) do not detract too much from the benefits of a complete fast, all while making it a lot more tolerable.
During my fasts, I supplemented with extended-release potassium (400mg four times per day), salt (3-5g per day), magnesium (600mg per day), and calcium (200mg per day).
However, I stopped all kinds of fasting because it negatively affected my vitality, which to me is more important than longevity. Over time, I realized that I had become, felt, and looked quite weak. I had very low levels of body fat and my vitality took a nose-dive. While I felt great during my fast, and perhaps the first day or so after, over the long run, my vitality had taken a nose-dive. My energy levels whenever I was not fasting, were much lower than they should have been.
They were probably caused by a combination of the following:
- Long-term reduction in leptin levels. I discuss my experience with leptin replenishment in more detail The Life-changing Power of Hormones..
- Long-term reduction in IGF-1 levels. I discuss my experience with growth hormone, an upstream signal to IGF-1 synthesis in more detail My Experience With Non-standard Hormones..
- Impairment in peripheral thyroid hormone sensitivity (measured by the ratio of T3/reverse T3). My experience with thyroid hormones is discussed here.
- A long-term decline in sympathetic nervous system activity and metabolism pointing to a potential “reprogramming” of brain energy homeostasis in POMC/AgRP neurons. I discuss this in more detail here: Why Weight-loss is Not About Calories In vs. Calories Out.
- Loss of muscle mass. I discuss my fitness regime in more detail here.
- All kinds of fasting, including intermittent fasting, can drive people towards eating disorders, in part because the “feeling proud of yourself” can be highly addictive.
I now believe that, similar to metformin, fasting is only great for people with ill metabolic health while its overall net positive effects on metabolically healthy people are questionable. It is unlikely that I will return to any kind of fasting anytime soon. I now believe that I can get most of the non-psychological benefits of fasting with rapamycin (discussed here) without any of the downsides listed above.
The major benefits I noticed were a feeling of accomplishment and a build-up of self-discipline. During my fasts, I usually became a productive demon completing about two weeks’ worth of tasks in only five days.
One thing I find worth noting is that during my fasts I was incredibly alert, which was probably due to multiple reasons.
- Firstly, when insulin levels are very low, orexin levels are disinhibited. Orexin is a neuropeptide causing wakefulness by projecting to a plethora of “wakefulness” transmitters such as histamine and noradrenaline.
- Secondly, cortisol and adrenaline levels are high because blood glucose levels need to be maintained. Cortisol causes gluconeogenesis and adrenaline causes glycogenolysis. Both cortisol and adrenaline cause a wakeful alertness.
- Thirdly, sympathetic nervous system activity is high because, among other things, body temperature needs to be kept at equilibrium. Alertness correlates well with SNS activity.
Is fasting “bad”?
As so often, everything depends on the context. I am lean, metabolically healthy, and athletic. Fasting has a much higher cost/benefit ratio for me vs. someone who is overweight, insulin-resistant, and sedentary.
The wider picture, however, is that maintaining a healthy body weight is one of the most important things one can do for long-term health. It’s highly likely that, if fasting is the way that works for someone, then the downsides are probably worth it compared to the downsides of long-term obesity.
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Sources & further information
- Clinical study: Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease
- Experience Report: How Intermittent Fasting Saved Me…While Slowly Killing Me
Disclaimer
The content available on this website is based on the author’s individual research, opinions, and personal experiences. It is intended solely for informational and entertainment purposes and does not constitute medical advice. The author does not endorse the use of supplements, pharmaceutical drugs, or hormones without the direct oversight of a qualified physician. People should never disregard professional medical advice or delay in seeking it because of something they have read on the internet.