Of Monkeys and Micro
By Bryan Caplan
Calorie restricted diets demonstrably increase the lifespans of yeast, fish, rodents, and dogs. Will they work for humans? For obvious reasons, controlled human experiments are problematic. Researchers therefore turned to the next best thing: experiments on non-human primates – rhesus monkeys to be specific. Two major studies began in the late 1980s – one in 1987, the other in 1989. The main results are now in: calorie restriction failed.
Results from the 1987 study are openly negative:
It turns out the skinny monkeys did not live
any longer than those kept at more normal weights. Some lab test results
improved, but only in monkeys put on the diet when they were old. The
causes of death — cancer, heart disease — were the same in both the
underfed and the normally fed monkeys.
Lab test results showed lower levels of cholesterol and blood sugar in
the male monkeys that started eating 30 percent fewer calories in old
age, but not in the females. Males and females that were put on the diet
when they were old had lower levels of triglycerides, which are linked
to heart disease risk. Monkeys put on the diet when they were young or
middle-aged did not get the same benefits, though they had less cancer.
But the bottom line was that the monkeys that ate less did not live any
longer than those that ate normally.
Results for the 1989 study are superficially positive but substantively negative.
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,
My question for you: How do these results make you feel? Most people react with joy. “Yay! The dietary change I definitely don’t want to endure doesn’t work anyway!” On reflection, though, reconciling this elation with basic microeconomics is extremely difficult.
Calorie restriction is a choice – an option. The better calorie restriction works, the better your options. The evidence that calorie restriction does not work implies that we are effectively poorer. Living longer by half-starving ourselves is off the menu.
You could object, “I’d rather live a normal, pleasant lifespan than a long lifespan of constant hunger.” If that’s your story, though, you should at least be indifferent to the outcome of the research. Furthermore, if you care even slightly about people who value longevity more than a full belly, the failure of calorie restriction is still bad news. You’re no worse off, but people you care about are poorer than you thought. On reflection, only misanthropes have a reason to jump for joy.
What’s going on? This seems like a classic case of cognitive dissonance. Once you make up your mind to do X, thinking about the advantages of Y makes you unhappy. The conclusion that X is better than Y all things considered does not put our minds to rest. We feel best when we conclude that X is better than Y in all respects.
Not convinced? Imagine that researchers discovered that calorie restricted diets made us immortal. Would any sane person consider this bad news? No way. Even if you’d rather die than endure an eternity of hunger, you almost surely care about someone who’d happily make that trade-off.
Of course, there’s another sense in which we should be happy about the negative results. Given that calorie restricted diets don’t work, we should be happy to discover the truth so people can stop suffering in vain. Basic microeconomics doesn’t just imply that more options are good. It also implies that false hope is bad.