I was just at university reading a paper called “Why Do We Age?” by Tom Kirkwood and Steven Austad (which you can download and read here). In the paper, the authors explore an evolutionary explanation for ageing, by arguing that senescence is not the product of “inevitable biological wear-and-tear”. They don’t claim that ageing is adaptive in any way, but rather that it is a byproduct of the biased allocation of resources towards the beginning of life (this is called the “disposable soma hypothesis”). As the likelihood of survival decreases as a wild animal gets older (due to extrinsic factors, such as predation), there are less selection pressures on the mechanisms that regulate cell maintenance later in life. Evolution only cares about keeping the animal in good condition as long as it might survive in the wild. As a result, as the animal gets older, damage to cells accumulates and senescence sets in.

That’s all well and good, and the paper then goes on to list the predictions about what we should see in the wild. The first is that animals raised in environments safe from predators should demonstrate slower ageing. This has been found by studying possums across two islands that differ in predation: if there are less predators, the possums age slower. Another prediction is that if you restrict reproduction to later in life, you should also see slower ageing. This has been found in fruit flies.

But there’s another prediction that made me do a double take. It states that organisms should be adapted to vary their own ageing depending on environmental factors, such as periods of famine that they may be unlikely to survive. If times are tough, it will improve your fitness to fix your body more. Evidence in support of this has been found in roundworms, whose larvae will develop into a half-adult “dauer” (with a life expectancy of around 60 years, compared to 17 years for normal adults) if there’s low food availability in the environment.

But then I saw this sentence: “It is well known that reduced calorie intake slows ageing in laboratory rodents…” Say what now? I wasn’t told about this! It makes sense with the theory, but I was still curious. So I looked at the referenced paper, and the effect seems legit and well-documented. And then I started thinking… okay, could the same apply to humans? Rodents and humans are very similar genetically and neuroanatomically, so it’s not too far of a leap to make.

Could you give up pizza in the hope of longer life?

I opened the floodgates. A quick internet search revealed a tonne of websites dedicated to calorie restriction without malnutrition as a method of increasing human life expectancy, with links to papers that support this notion. I haven’t read any of the papers myself, but it just seemed really counter-intuitive and amazing to me. I don’t know how I hadn’t heard about this sooner! But apparently the effect can be huge, increasing your life by up to 5-10 years (if you can extrapolate from rodents and primates, which we can’t be sure of). I’d like to see some published longitudinal studies before believing anything, but it’s still a pretty neat idea.

So then comes the kicker. Let’s say that these studies were done, and it turned out you could actually increase your lifespan by restricting your diet. The effect becomes documented. It’s a fad everywhere. This ends up being the Philosopher’s Stone of evolutionary medicine. Would you get involved with such a diet? Or do you love food too much? I don’t know about you, but I think I’m swaying towards the food end…