Aging might be said, to paraphrase von Clausewitz, to be a mere continuation of growth by other means.
The process of aging still holds many mysteries, but we can say with some certainty that there is a trade-off between growth and longevity. The more growth that occurs, the faster and greater the aging. Within species, bigger animals age faster and die younger, and this holds true in humans. This is probably why men age faster and die younger than women: men are bigger, and as such have experienced more and faster growth. Shorter men live longer.
Professional (American) football players, who are known for their huge size, die at the average age of 55. Or it might even be 51. (There’s lots of talk about head injuries, which football players undoubtedly suffer from, but the idea that that kills them in their 50s strikes me as implausible. Muhammad Ali is still alive, and I’d bet he’s taken a lot more and more powerful shots to the head than almost any football player. N=1 of course.)
The average age of death of a sumo wrestler is around 63, about 15 years younger than the average Japanese man.
Whatever the mechanism of action or even whatever the ultimate truth is about the relationship between growth and longevity, plenty of evidence for it exists.
It seems that one of the reasons for the relationship lies with the growth hormone IGF-1. This hormone causes increased growth, but at later ages, increases the rates of cancer. IGF-1 activates mTOR (Nature Cell Biology), which in turn is implicated in “cancer, atherosclerosis, hypertension, heart hypertrophy, osteoporosis, type II diabetes, obesity, Alzheimer’s and Parkinson’s diseases, age-related macular degeneration, osteoarthritis and other diseases.” (Cell Cycle.)
Higher levels of IGF-1 make for a robust human being, able to survive the threats of infectious disease and wounds. But most of us are no longer in an environment where these threats are paramount. Those football players would likely be able to survive a battle or a plague better than others, but the consequence is that they age faster. In fact, one of the reasons humans are living longer is probably because the threats of infection and wounds are low, and slow-growing people with less robust constitutions who may not have been able to survive those threats now live longer, and age slower. (Aging.) In essence, there are more slow-aging people around because we’ve reduced the threats of infections and wounds.
On the other hand, with age comes a lack of vigor, susceptibility to infection, atrophy of muscles, bones, and brain, all around general deterioration of the body and of quality of life. Much of this can be traced to an increasing inability to repair and regenerate tissues.
Sarcopenia, or muscle wasting, is a very common affliction in the old, and can be devastating. Osteoporosis, the wasting of bone, is another common affliction.
As it happens, IGF-1, the same growth hormone that appears to increase aging, may also treat the diseases of atrophy seen in old age. Circulating levels of IGF-1 directly regulate bone density (Journal of Clinical Investigation), and therefore higher levels of this hormone may help prevent osteoporosis. Sarcopenia may be ameliorated with higher levels of IGF-1. (Mechanisms of Ageing and Development.)
Levels of IGF-1 are inversely correlated with measures of cognitive decline; the more IGF-1, the better the mental function in people aged 65 to 86. (Neuropsychobiology.)
So, I’d say we need balance. Intermittent fasting can lower levels of IGF-1, and hence slow the aging process and improve health biomarkers. But, if fasting isn’t done carefully, and followed by periods of adequate protein nutrition and exercise, preferably resistance training, it could potentially lead to muscle and bone loss and frailty.
Successful implementation of anti-aging must be carefully done. A useful analogy might be with exercise; too little leads to poor health, and too much – such as extensive distance running – can lead to damage.
The program I outlined in my anti-aging book seeks to balance the increase in autophagy brought on by fasting with a renewal of lean tissue through diet and exercise.
We want to slow or reverse the aging process so we can live longer lives in robust health, not so we can spend more years in a nursing home.