Caloric restriction (with adequate nutrition) is the only non-pharmacological intervention that extends the lifespan in model organisms from yeast to mammals. Among other things, CR downregulates the mTOR pathway and upregulates AMPK, both of which are metabolic master switches.
In laboratory animals, CR impressively prolongs lifespan. However, lifespan increases are consistently more pronounced in shorter-lived animals than in longer-lived ones. For example, while CR may increase mouse lifespan by 30-50%, it is thought to only increase lifespan by 10% or so in dogs, likely even less in humans.
However, it should be noted that this holds for laboratory animals. In the wild, CR may even shorten lifespan because of immunosuppression and poor wound healing. Another downside of caloric restriction is that it causes corticoatrophy, as observed in monkey studies. However, it is unclear how much of this is due to CR itself and how much is attributable to low levels of neurotrophic hormones such as estradiol, T3, leptin, and IGF-1.
I discuss these aspects in much more detail in my article on Bryan Johnson, The World’s Most Expensive Eating Disorder.
Personal experience with caloric restriction
A couple of years ago, I used to restrict my calories to about 2000-2200kcal/d. Nothing else I have ever done (and I have done a lot) has worsened my health and well-being as much. I was constantly ravenous, developed a slow metabolism (low heart rate, blood pressure, body temperature), stubborn hormonal problems that took a long time to recover from, I had always cold hands and feet, and I was fatigued around the clock.
The ensuing hypoleptinemia also made me irritable, neurotic, restless, and obsessive, pulling me towards disordered eating. I discuss my experience with leptin replacement in more detail here.
For me, as a lean, metabolically healthy, and active young male, caloric restriction did way more harm than good. In fact, I cannot think of anything good it did.
- My energy levels were about as high as the energy levels of my 85-year-old grandpa. While I did my exercise religiously, I did not have any energy left for the other things that make life worth living.
- I noticed sweeping personality changes, and at times I felt like I had no personality anymore. I stopped being fun to be around, I mostly wanted to withdraw and be by myself (I am quite a social person normally), and I became rigid in my thinking and acting. These changes were presumably mediated by low leptin levels (discussed here).
- Despite the lethargy, I was also quite restless, driven, and my mind was racing all of the time. I had an irresistible urge to always be productive (presumably a proxy for “foraging behaviors”). I needed to exercise vigorously only to feel normal.
- A lot of my mental brainpower was taken up by food and I was always hungry. When I then ate “shitty” food (e.g., ice cream, fries), I felt like I was on amphetamine.
- I had lower levels of T3, testosterone, IGF-1, and leptin, all of which are crucial to proper immune function. While this might not be a problem for lab animals (on which the research is done), this might be different for animals in the wild (e.g., me), as I am more prone to infections. In fact, during the winter, I got one cold after another whereas I normally rarely to never get colds.
- My IGF-1 levels were about half of what they are normally. IGF1 levels are crucial for all aspects of brain health.
- My sex hormones were in the gutter and my SHBG rose to very high levels. My sex drive was non-existent.
- I lost muscle mass and had I been doing this for longer, my bone density would presumably also have declined.
- Lastly, CR was terrible for my quality of life. Personally, I want to feel vital, eat foods I enjoy, and prefer not to be tired, cold, and miserable all of the time.
If one reduces the caloric intake in humans who would otherwise be overeating (which is not the same as caloric restriction), getting them down to a healthy body weight will improve chronic disease, metabolic health, blood pressure, and brain health. It, therefore, has many longevity benefits. However, once people are already lean and metabolically healthy, in my opinion, CR does more harm than good.
I believe that I can achieve most of the benefits of CR (or fasting) with rapamycin, and also in a safer, more sustainable, and much more comfortable way.
Related articles
Sources & further information:
- Website: Bryan Johnson – Blueprint
- Website: Wikipedia – Caloric Restriction
- Scientific review: The ups and downs of caloric restriction and fasting: from molecular effects to clinical application
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.
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