Preventive Medicine Column

Dr. David L. Katz

Just in time for Valentine’s Day, epidemiology has given “sweetheart” a whole new meaning with a study demonstrating an association between sugar intake and heart disease. In deference to the holiday, we might repine the prosaic dispassion of epidemiologists inclined to replace boxes of chocolates with prescriptions for statins.  But epidemiologists, presumably, need love too, even if they have an odd way of showing it. So we’ll let them be, and move on to the study and its implications.

Like much nutritional epidemiology, the study in question was observational and therefore does not, and cannot, prove cause and effect. It merely showed more cardiovascular mortality among people with a higher percentage of calories coming from added sugar.  That may mean that sugar causes heart disease (I suspect it does contribute).  It may also mean that diets higher in sugar are just poorer diets- and people with poorer diets are more prone to heart disease.   That is somewhat less than astonishing.

We have long known that excess sugar intake is associated with obesity, insulin resistance, metabolic syndrome, and diabetes.  And we have long known that diabetes is among the most potent of risk factors for heart disease.  Leaving aside the prior studies that directly address the link between sugar and heart disease, we are left to wonder: how could excess sugar intake NOT be associated with heart disease?  That it must be is clear to all who recall the transitive property we learned in 6th grade algebra- if A leads to B and B leads to C, then A leads to C.  “A” here is sugar, “B” can be diabetes, and “C” is cardiovascular mortality.

The trouble with the “study generates publication; publication generates headlines; headlines generate blogs; blogs generate tweets, which generate more blogs and tweets…” cycle is that it makes it seem as if every incremental addition to the sum of what we know is a brand new, stand-alone, alternative truth.  That’s nonsense.  Worse, it’s dangerous nonsense- because there are many more “one nutrient at a time” ways to eat ourselves to sickness and premature death than there are to eat ourselves healthy.  As a culture, we seem committed to exploring them all.

Of course excess sugar is associated with heart disease.  But the importance of sugar intake to health does not obviate the importance of other factors.  Some of the same researchers involved in the new study have published other observational studies showing associations between meat and heart disease; meat and diabetes; processed meat and cancer; more fruit intake with less diabetes; more nut intake with less heart disease; and so on.  These results don’t disappear when new ones are published.  Notably, researchers at Harvard also studied the association between the nutrition guidance system I helped develop and health outcomes, and showed that the higher the overall nutritional quality of foods in general, the lower the rate of chronic disease and premature death from any cause.

Just like ingredients in a recipe, research results must be blended appropriately to avoid half-baked nonsense.  Nutrition makes the most sense when viewed holistically, and so does health.

In the service of both, then, I offer up my sound bites of ingestive truth intended to stand the test of time.  You can be the judge. Chew on them, and either swallow or spit as the spirit moves you:

1)    We can never get to good diets, or good health, one nutrient (or food) at a time.

2)    What’s genuinely good for any part of us is just plain good for us.

3)    What’s just plain good for us is good for every part of us.

4)    What’s genuinely bad for any part of us is just plain bad for us.

5)    What’s just plain bad for us is bad for every part of us.

6)    Getting a higher percentage of calories from X means getting a lower percentage of calories from Y.

7)    Our health is affected for good or bad both by what we don’t eat, and what we do eat in its place.

8)    The dose makes the poison.*

9)    There are many nutrition details we don’t know, but we know enough to eat well; we are not clueless about the basic care and feeding of Homo sapiens.

10) If you want to get out of the woods, it helps to see the forest through the trees.


As for the timing of those unromantic epidemiologists, inveighing against sweet hearts just in time for Valentine’s Day- they’re just doing their jobs, and probably not as heartless as they seem. We can take comfort in the fact that dark chocolate is still good for our hearts, as are strawberries. And to my knowledge, there’s never even been a question about love.




Dr. David L. Katz