Recently, the US Food and Drug Administration, working with the Institute of Medicine, has been considering a change in the regulatory status of salt. The FDA cannot currently restrict the amount of salt that can be added to processed foods, and the proposed change would allow them to do so.
Advocates of the proposed regulation, like former FDA commissioner David Kessler and the Center for Science in the Public Interest, argue that reducing the sodium in foods would improve people’s health and cut public health spending. Opponents argue that the evidence supporting health benefits of sodium reduction is by no means conclusive, and that attempts to reduce sodium intake could actually be harmful.
But a recent study by University of California, Davis nutritionists concludes that it may not even be possible to reduce salt intake through regulation. The study shows that people are naturally inclined to regulate salt intake to physiologically determined levels by unconsciously selecting foods to meet their needs.
According to the study, measurements collected from over 19,000 individuals from 33 countries worldwide indicate that daily sodium intake is confined to the relatively narrow range of 2,700 to 4,900 mg, with the worldwide average of 3,700 mg. This challenges the widely held belief that daily sodium consumption in the United States, which averages about 3,400 mg, has reached extreme levels.
The study also cites decades of research describing the specific mechanism by which the central nervous system, acting together with several organ systems, controls our appetite for salt.
In one cited study, a group of nearly 600 participants took part in what was to be a 3 year sodium intake intervention, with the goal of reducing daily intake to 1,850 mg. After the first 6 months, researchers noted that participants were unable to reduce sodium intake below about 2,750 mg per day—close to the bottom of the range the UC Davis study identified.
Another study had similar findings. In this study, subjects, through intensive dietary counseling, reduced their daily sodium intake to an average of 1,775 mg over 4 weeks. The subjects were then randomized to receive either a 2,300 mg sodium tablet or a placebo, while still receiving counseling.
When taking the placebo, average sodium intake stabilized around 2,750 mg—again very close to the bottom of the identified range. This means that subjects naturally increased their sodium intake when blinded to their treatment. When this group was switched over to receive the 2,300 mg sodium supplement, daily intake rose to only 4,050 mg, far less than the predicted 5,050 mg. This suggests that subjects naturally reduced their dietary sodium intake without consciously intending to do so.
The UC Davis study goes on to cite a number of surveys indicating that sodium intake in the United Kingdom has "varied minimally" over the past 25 years, despite a costly Food Standards Agency campaign to reduce sodium intake in the UK.
The Institute of Medicine says that daily sodium intake should not exceed 2,300 mg, and new guidelines to be released in 2010 may set the recommended maximum even lower. Any regulatory action taken by the FDA would presumably aim to reduce intake at least to this 2,300 mg level, even though it is 17 percent lower than the bottom of the range the UC Davis study identified, and a full 38 percent lower than the worldwide average.
Given the findings of this study, it seems likely that regulation restricting sodium in foods would be ineffective because people would unconsciously adjust their diets to compensate. As the study puts it, "[sodium intake] is unlikely to be malleable by public policy initiatives", and attempts to change consumption would "expend valuable national and personal resources against unachievable goals."