Taking Nutrition Studies With a Grain of Salt

If there’s one thing that confounds the general public—and perhaps many in the food industry, as well—it’s the often conflicting nutrition research news. The most recent example? Salt.

In July, the American Journal of Hypertension published a study—“Reduced Dietary Salt for the Prevention of Cardiovascular Disease: A Meta-Analysis of Randomized Controlled Trials (Cochrane Review)”—that concluded, contrary to popular belief, dietary salt reduction has no effect on strokes or heart attacks. This led to the inevitable headlines of “Review raises questions over benefits of cutting salt” and “Now salt is safe to eat—Health fascists proved wrong after lecturing us all for years.”

But in August, commentary in The Lancet (“Salt and Cardiovascular Disease Mortality”) refuted the conclusion of the Cochrane Review, saying: “This study is disappointingly weak and contributes little to our understanding of salt and disease. It is likely to confuse public perceptions of the importance of salt as a risk factor for high blood pressure, heart disease and stroke. Questions of intervention and outcome, such as sodium intake and CVD events, cannot be answered by small observational studies. It is dangerous to jump to conclusions on the basis of single studies and ignore the totality of evidence.” In fact, a reanalysis of the Cochrane data found that reducing salt intake can lead to “a significant reduction” in cardiovascular events.

So, how should the industry respond? Perhaps the best answer is to be found in a recent article on the Harvard School of Public Health’s website, The Nutrition Source, “Nutrition Research and Mass Media: An Introduction” (hsph.harvard.edu/nutritionsource/nutrition-news/media-full-story/index.html). While aimed at consumers who want to decipher the media’s version of research, it’s a straightforward discussion for those designing healthier foods and beverages:

The research process is like placing stones on an old-fashioned balance scale. When enough weight accumulates on one side, the scale tips in favor of a particular recommendation. And the more weight there is on one side, the stronger the recommendation is and the more evidence it would take to change it.

The paper cited the link between alcohol and heart disease as an example of an established relationship.

But not all topics are as clear-cut as this. Often, the weight of evidence is not as great. In some cases, only a handful of studies have addressed a particular question. In other cases, a large number of studies may support one side, but there may be some particularly significant studies supporting the other side as well—just enough to cast some doubt. In these instances, we’d say that there is a probable link between a behavior and a disease.

Eating nuts to protect against heart disease was given as an example of a probable link.

I highly recommend reading the full paper.

The takeaway is, in addition to reading the public’s pulse, we all need to do a little more-judicious review of the studies that are fueling the public’s perception and follow the science.