September 29, 2020

The Niche

Knoepfler lab stem cell blog

Caloric restriction: dieting monkeys teach human scientists?

The notion of caloric restriction (CR) as a means to prolong human life is intriguing.

The basic idea of CR is that if you eat a lot less than the average person you’ll live longer. You might even live a higher quality, healthier life.

But is this true? (update: see my newer post on 5 possible natural stem cell boosts).

A whole bunch of scientists and even more dieting monkeys have been part of a very large, very expensive (as in millions of dollars; see image below from the National Institute on Aging) research effort to answer this question. A paper in 2009 on monkeys suggested CR worked.

Caloric Restriction in monkeys
Caloric Restriction in monkeys didn’t prolong life.

But yesterday we heard that the latest study on the monkeys pretty conclusively indicated that at least in monkeys, which are very similar to humans, caloric restriction to put it simply failed to work. It did not prolong life.

The best write up I’ve seen on this is from one of my favorite science writers, Gina Kolata, over at the NY Times. I highly recommend it.

Perhaps the “good news” coming out of this study is that humans can enjoy eating in moderation and do not have to adapt some extreme CR approach to life that leaves them forever hungry.

What I find most fascinating coming out of this arena has nothing to do with CR itself, but rather I think this bunch of dieting monkeys has more to teach us about human scientists than anything else.

The CR studies reveal some sobering realities about the traps that we human scientists can fall into if we are not extremely careful.

Let’s go back 3 years to that first major monkey study, published in Science in 2009 by a team from the University of Wisconsin.

The study concluded that CR prolonged life and it made huge international news. Iit was a bombshell of a story.

However, many people believe the study came to the wrong conclusion, in fact an exaggerated or hyped conclusion.


Gina Kolata hits the nail on the head:

But even that study had a question mark hanging over it. Its authors had disregarded about half of the deaths among the monkeys they studied, saying they were not related to aging. If they had included all of the deaths, there was no extension of life span in the Wisconsin study, either.

In other words, the scientists doing the monkey CR aging study published in 2009 (what Kolata refers to in this passage as “that study”) eliminated more than half of the death data and specifically that data which didn’t fit with their hypothesis that CR lengthened life. As a result, the scientists most likely in my opinion came to the wrong conclusion.

Why would they do this?

In this regard, Kolata quotes Steven Austad of Univ. of Texas in San Antonio in this passage:

the University of Wisconsin study “was not nearly as conclusive as it was made out to be” and that the new study casts further doubt on the belief that caloric restriction extends life.

There is a potential trap in science of becoming married to a hypothesis, becoming emotionally invested in it. Another way of putting it is that some scientists sometimes make the mistake of deciding in advance what their studies should prove rather than letting the data itself tell the story.

I think this has happened in the CR research field to some scientists and that 2009 study is a telling example. Others in the CR field have remained more objective.

Part of the reason I think some scientists are too emotionally attached to CR is that they themselves started CR on themselves too.

So amazingly, some of the scientists studying CR in monkeys, also in essence started doing concurrently personal experiments on themselves also with CR. At some point one has to wonder if they lost their objectiveness.

In the cancer field it would be akin to scientists who deeply believe that a certain new drug, Drug X, prevents cancer and who are studying Drug X in rodents predisposed to get cancer, also starting taking Drug X themselves at the same time they were studying Drug X in rodents. When put that way, to me it seems particularly concerning.

Kolata digs deeper and finds that some earlier rodent students on CR, which the CR scientists had so often referenced, perhaps were also showing CR had no effect on lifespan. When the mouse studies showed no benefit of CR on lifespan (or even shortened lifespan in some mice), some of the CR scientists tried to undermine those studies as Kolata describes:

The response to that study was “absolute disbelief,” Dr. Austad said. “Even though the authors are well-respected calorie restrictors, people said the result was not interesting, that there was something weird about the mice.”

The weight of the evidence suggests that some groups in the CR field had become emotionally attached to CR and lost some of their objectivity. When the data didn’t fit with their hypothesis that CR extended life they ignored it.

It’s pretty clear that quite a number of CR scientists have become too attached to CR and it has changed the way they do science.

One CR scientist even described himself as “a hopeless caloric-restriction romantic”.

The story on CR and lifespan is not resolved and perhaps there is some subtle effect of CR on lifespan and aging, but if there is an effect of CR it is unlikely to be major for most primates including humans. We’ll see.

However, what is clear from the CR studies is that scientists are just as human as any one else and sometimes fall into the trap of wanting their hypothesis to be true so badly that they veer off course from rigorous scientific method.

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