Last week, researchers published findings from dietary data collected from thousands of individuals over 40 years, saying that only nine people out of 20,000 ever met the joint guidelines for both sodium and potassium – and even then, only within diets that lacked in other respects. Have we set the bar too high?
The Dietary Guidelines for Americans are revised every five years to reflect the latest scientific evidence around diet and health. When the latest guidelines appeared at the beginning of last year, it was clear that most of us could do a lot to improve our diets.
For sodium, the recommendation is an upper limit of 2,300mg, with a lower limit of 1,500mg for those considered at risk of heart disease. About half of the US population falls into this at-risk group. Recommended potassium intake across the board is 4,700mg, and most of us average 2,400mg to 3,200mg a day. But while individuals and food manufacturers alike may be at pains to reduce sodium intake in particular, it is worth asking, how did we get to recommendations for some nutrients that 99.99% of the population fails to meet ?
Of course, there’s nothing wrong with suggesting that Americans generally eat way too much sodium and not enough potassium. There is a large body of evidence suggesting that this is certainly the case for most of us.
However, if the standards set are virtually impossible to achieve, it seems to me that we have indeed set the bar too high.
In an earlier study , the same researchers found that they could not design even a hypothetical diet containing less than 1,500mg of sodium that still included enough energy for anyone under the age of 50. The higher 2,300mg limit was possible, but only with significant changes to dietary patterns.
Researchers involved in developing the Dietary Guidelines for Americans may argue that their job is to define nutrition profiles that would best mitigate disease risk. But we are not hydroponic plants slurping from a carefully balanced nutrient-rich solution. We live in a food environment that does not allow us to hit these targets.
In designing guidelines, we must not ignore the way we actually eat, which foods are available to us, and which are affordable. Even if 1,500mg of sodium were perfect for many of us for ideal health, ideals are only valid if they reflect the possibilities of the food supply, and they should be constrained by them.
Holes in dose-response data
There are also some pretty big questions raised by the Dietary Guidelines Advisory Committee in its assessment of the evidence around sodium and health. It said that there was strong evidence that as sodium intake decreases, so does blood pressure. (Other research suggests that this is the case, but only up to a point.)
However the DGAC added that there was a need for dose-response trials for sodium, for potassium, and for interactions between the two. Certainly alongside questions of feasibility, this should sound alarm bells about making recommendations for single nutrients without whole-diet context.
Research is underway that will influence the shape of the 2015 version of the Dietary Guidelines for Americans. Before these next guidelines are released, real-world assessments of our food habits should lead us to question the role we want them to take – are they intended to provide realistic guidance for Americans? Or are they purely academic?