Caloric Restriction


This article is one of many similar stories from recent years. They are all – some more loosely than others – based on caloric restriction (CR).

What is CR?

Caloric restriction involves eating significantly less calories while still getting all the required nutrients. In other words, eating less without becoming malnourished.

vegetable women for CR
Image source:

Sounds pretty  miserable, but its effects can be remarkable.

CR is the only method that can slow down aging in a variety of living things. It increases lifespan and so-called healthspan – when a living thing is generally healthy and free from disease.

In short, caloric restriction can keep living things healthier, for longer.

In the 1930s researchers were already investigating the effects of CR in rats. Countless studies since – in dogs, mice and even yeast – tell a similar story. Restricting calories can extend lifespan, and delay the onset of disorders associated with aging, like diabetes and bone loss.

In 2014, things got a little closer to home. A study showed that caloric restriction had similar effects in rhesus monkeys, providing the first evidence that CR can delay aging in primates. Big news for this guy, and potentially for us, too.

rhesus monkey CR
Image source: 13bobby via Flickr

Next question – how?

The simple answer is we don’t know how CR works. There are many different ideas, but here’s a few of the more interesting ones:

  • Hormesis: the idea that exposing a living thing to low levels of stress can make it resistant to higher levels of stress. Some research suggests that CR acts in this way to protect animals from the diseases of aging. But what is this “stress”? Mice don’t usually have essay deadlines.
    There are different biological stresses, and one – called oxidative stress – has been linked to CR. *science-y bit* Some processes in cells produce molecules called reactive oxygen species. They can be toxic, and if cells cannot clear up (or use) these molecules they will enter a state of oxidative stress. This type of stress increases as we age.
    One study on a tiny worm called C. elegans showed that CR increased its lifespan, mainly by increasing oxidative stress. It seemed to make the worms resistant to the higher levels of oxidative stress that occur with age.
  • Evolution: during a famine, the body focuses more of its energy on repairing itself and less on making babies, in an attempt to keep you alive. Some people think that a similar thing occurs in CR – by repairing itself, the body can keep going for longer. It’s a pretty broad idea, and famine isn’t strictly CR (it usually involves malnutrition). However, this theory is supported by some studies; caloric restriction in humans reduces levels of testosterone, a sex hormone. Less food and less baby-making?! What a life.
  • Sirtuins – these molecules are found in various living things, from bacteria to humans. They have roles to play in many processes, including stress resistance and aging. One sirtuin in yeast (Sir2) seems to be important to how CR affects aging. We know that CR can increase yeast lifespan, but if we remove Sir2 and then restrict calories, lifespan doesn’t increase. As is often the case in science (more often than we’d like to admit), we’re not sure why.
empty fridge CR
Image source: Global X via Flickr

Before we clear out our fridges, can CR really work in humans?

The media seem to think so, but often miss a key point. CR is not yet proven to extend lifespan, or delay the onset of age-associated disease, in humans.

Ok, it works in some species, so it might work in humans. But we can’t be sure.

Unsurprisingly, some people have ignored this. One group, imaginatively named the CR society, actually dedicate their lives to caloric restriction.

News stories about the benefits of caloric restriction are common, and thankfully many advise caution. The long-term effects of CR in humans are unknown, but cutting calories increases risk of malnutrition. This has its own risks, such as muscle wastage, aneamia and even infertility.

Should we believe the hype? 

Caloric restriction (without malnutrition) may slow aging in humans. But until this is proven, we need to be careful. Promoting a dramatic lifestyle change is irresponsible and potentially dangerous.

Don’t believe everything you read (oh, the irony).


man eating burger CR
Image source: Nick Taylor via Flickr

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