Does the “Rate of Living Theory” Hold up to Scrutiny? And What Does it Imply About Exercising?

by Nils Osmar. April 18, 2023  Medical Disclaimer

The “rate of living theory” (ROL) suggests that people (and other complex organisms) “have a finite number of breaths, heartbeats, or other measures, and will die once they’ve used those up.” Its proponents view it as a universal principle explaining the differences in lifespans between different species.

There’s some reason to view it as an accurate summary, at least in its broad strokes. For example, small animals such as mice and shrews have rapid heartbeats, metabolize oxygen quickly, and tend to have short lifespans. (They have fast metabolisms, use up their allotment of heartbeats early on, and die young.) Large, sluggish animals such as elephants and tortoises have slower heartbeats, metabolize oxygen more slowly, and tend to have longer lifespans.

Some cite insects as further proof of the ROL theory: they’re tiny and most of them have very short lifespans.

Problems with the theory

The problem for proponents of the theory is that when attempts have been made to prove that ROL is a universal principle, many of the studies have ended up casting doubt on it. If it’s true, it should hold up in all circumstances, but it does not.

  • Most insects die young, but some, like queen ants, live thirty years (almost half of a human lifespan). Queen termites have been found to live 13 years. Queen bees live 5 years. And high metabolic rates does not explain the short lifespans of other insects; most actually have low metabolic rates. See study: Do insect metabolic rates at rest and during flight scale with body mass?)
  • Birds are much smaller than people, yet some of them live as long as we do. A parrot’s heart can beat up to 600 times per minute, much faster than a human’s, and their bodies are tiny compared to people, so parrots should in theory die much sooner than we do. Yet some parrots have been found to live to be 75 years old.
  • Rats and mice tend to have short lifespans. But naked mole rats, that are about the same size, can live to over 30 years old — 500 percent longer than would be expected if the theory were universal. If all animals have a set allotment of heartbeats, and this is a basic, universal rule, why do some birds and mammals ignore and disregard it?

Why it matters

  • Most people in the life extension community agree that health and fitness are important to longevity, and support, for example, moving and exercising. Our metabolism slows as we age, part of a general “winding down” as we approach end of life. Many anti-aging interventions focus on trying to reverse this slow general decline.
  • People who center their thinking in the ROL theory tend to caution against exertion, maintaining that if we “use up our heartbeats by exercising,” it will shorten our lifespans. If the ROL theory were accurate, in their POV, it might make sense to lie around like sloths instead of exercising. (Musn’t use up our heartbeats!)
  • But there’s no evidence that “couch potatoes” are setting longevity records. Being sedentary instead seems to set us up for diabetes, heart disease, early Alzheimer’s, and other diseases of aging.

According to this summary article from Harvard Press, which cites several studies as sources, exercising is an effective way to add healthy years to our lives.

From the article:

The study, published July 25 in the journal Circulation, analyzed 30 years of medical records and mortality data from more than 100,000 adults enrolled in the Nurses’ Health Study and the Health Professionals Follow-Up Study. Researchers found that people who followed the minimum guidelines for physical activity—150–300 minutes per week of moderate-intensity activity, or 75–150 minutes per week of vigorous-intensity activity—reduced their risk of early death by as much as 21%. But people who exercised from two to four times the minimum were able to lower their risk by as much as 31%.

“Our study provides evidence to guide individuals to choose the right amount and intensity of physical activity over their lifetime to maintain their overall health,” said Lee, research associate in the Department of Nutrition and first author of the study, in a release.

Read the American Heart Association release: Getting more exercise than guidelines suggest may further lower death risk

Read a CNN article: Exercise more than the recommended amounts for the longest life, study says

Read a Psychology Today article: New Study Pinpoints How Much Exercise We Need to Live Longer

Studies casting doubt on ROL

  • While the ROL theory is supported by broad observations, several of the studies that have been conducted in attempts to prove it have instead ended up casting doubt on it.

Study 1: No evidence for the ‘rate-of-living’ theory across the tetrapod tree of life

From the study:

Our findings did not support the predictions of the rate-of-living theory. Basal and field metabolic rates, seasonality, and activity times, as well as reptile body temperatures and foraging ecology, were found to be unrelated to longevity.

We conclude that the rate-of-living theory does not hold true for terrestrial vertebrates, and suggest that life expectancy is driven by selection arising from extrinsic mortality factors. A simple link between metabolic rates, oxidative damage and life span is not supported.

Study 2: Mammalian Aging, Metabolism, and Ecology: Evidence From the Bats and Marsupials

From the study:

Our results fail to support a rate of living theory of aging in either a weak or strong form.

The strong form suggests that mass-specific energy expenditure per life span would be approximately equivalent across species. For 164 mammalian species, energy expenditure per lifetime ranges from 39 to 1102 kcal/g/life span. Within bats, there is nearly a fourfold range of lifetime energy expenditure while among marsupials the range is nearly tenfold. Thus even within mammalian orders, this generalization seems not to hold.

A weaker form of the same idea holds that lifespan should be generally inversely related to metabolic rate. This notion predicts that: (a) marsupials should be longer-lived than similar sized eutherians; (b) heterothermic species should be longer-lived than similar-sized homeotherms, and (c) homeothermic bats should have life spans approximately equal to similar-sized nonflying eutherians. Our data fail to support any of these predictions

These results suggest that at least between species, there is an uncertain relationship between basal metabolic rate and aging. Therefore the finding that a proven life-extending treatment such as dietary restriction in laboratory rats and mice does not routinely reduce metabolic rate is perhaps less surprising than it otherwise might be….

It is clear from the preceding that there is no simple relationship between mammalian longevity and metabolic rate. Species with low or high metabolic rates may have evolved short or long life spans, depending upon their ecology.

Not medical advice

This article is not intended as, and should not be taken as, medical advice. I’m not advising that people eat any particular diet or take any particular supplement(s), just reporting on what I’m doing. Supplements, like medications and other interventions, can have side effects; I would encourage people to research both possible benefits and side effects before starting on any supplementation regimen, and consult with a medical professional about any issues which might have a medical component.  See full Medical Disclaimer

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