“In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in the case of poetry, it’s the exact opposite!”
                                — Paul Dirac

Gretchen Reynolds, in her chart on “Longer Living Through Science” does a good job of making science into poetry.  Full of qualifications and afterthoughts and 180^o reversals, longevity research makes an easy target for satire.  Reynolds herself has established herself as a consistent advocate for some of the clear messages concerning exercise and diet that come from this research.  As we smile, let’s remember that our lives and our health hang in the balance, and through all the contradictions, there are some persistent truths.

This chart was published in the New York Times Magazine on Sunday, summarizing the last four years of scientific studies concerning longevity.

The point of the chart is to convince us that longevity science is a hodge-podge of contradictory results.  The things that consistently lead to better health and longer life are beyond our control (genes, pollution, wealth).  Among things that are under our control, mere mortals cannot know what is effective (diet, exercise, smoking and drinking).

There are many reasons that specific items in the chart are not as inscrutable as they appear.  Reynolds cites only studies of the last four years, and current research is always focused on the unresolved questions, not the well-established basics. Studies based on human longevity are the gold standard, but they must be interpreted with care since they cannot be properly controlled.  (You can’t put humans in cages and vary one factor at a time.  This makes it difficult to disentangle the many correlated variables and draw conclusions about root causes.)  Studies of mice and rats are generally the best indication of what will work in humans.  Studies of flies and worms cannot be directly extrapolated to humans.  They are valuable for biochemical understanding and suggestions for further study; but most treatments that work to extend life in flies fail in humans.

Every result cited in the chart is, in fact, a subtlety, a nuance at the edge of what we already knew about behaviors that affect longevity.  Absent from the chart was the one result that is new, and a reversal of what doctors had been recommending for decades.  Standard doctors’ advice has been to minimize salt intake, and last year it was found that higher salt intake is associated with lower mortality.

Perhaps the most contentious area involves weight loss.  It’s an issue frought with emotion for most of us.  On the one hand, caloric restriction has been the most robust technique for life extension in lab animals for the last 80 years.  On the other hand, using will power to eat less doesn’t work for most of us, and in fact willpower has been found to backfire and produce weight gain more often than not.  Further complication comes from social prejudices against heavy-set women.  For most women, appearance is a stronger motivater than health, and this has produced an epidemic of unhealthy dieting.

I believe this phenomenon has a lot to do with why studies of BMI have failed to show any advantage to being skinny.  In fact, these results always underestimate the damage that is done by overeating.  

People’s weight is determined by a combination of genetics with diet and exercise.  But being congenitally overweight is not a health risk, while overeating and under-exercising are clear health risks.  There are “lucky” people who can overeat without gaining weight, and “unlucky” folks who are disciplining themselves to eat less and exercise more, because they fear that extra weight will make them unattractive.  These two people may have the same BMI, so they are lumped together in the statistics, but the latter will have much better health prospects than the former.  It’s a kind of poetic justice—regardless of cosmetic appearance, nature has been even-handed in rewarding temperance with health.

BMI studies should be re-scaled to separate genetics from life style.  In support of this idea, results from genetically obese mice indicate that they have exceptionally long life spans when calorically restricted, even though their appearance is not at all lean.

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Here are some uncontroversial recommendations from the community of scientists who study human longevity:

• For most people, smoking is a health risk and shortens life expectancy.
• Exercise contributes positively to every aspect of physical and psychological health, as well as longevity.
• Conversely, overeating, especially carbohydrates, has a negative effect on health and longevity.
• Community, engagement, love and relationships of caring have as great and robust a benefit for health and longevity as any physical factor.
• Anti-inflammatory foods and supplements have shown consistent benefits.

There’s much more on my Aging Advice page, including my personal recommendations that are not yet standard medical advice.

We all need help laughing at ourselves, and I’m happy to accept a poke from Gretchen Reynolds. But let’s not forget that we live in a culture that seduces us into the obsessive earning of money, consuming of food and entertainment, all distracting us from the basics of our health.