In 1977, The US Senate Select Committee on Nutrition and
Human Needs issued the 1st edition of Dietary Goals for the United
States. One of the recommendations was to: “Reduce
salt consumption by about 50 to 85 percent to approximately 3 grams per day”. This
equated to 1,200 milligrams of sodium, which is the element of salt (sodium
chloride) implicated as a contributory factor for the development of
hypertension. This is slightly below the current sodium recommendations of the
American Heart Association of <1,500 milligrams per day but is half what the
Institute of Medicine set out as a target for the US population in its most
recent report on dietary guidelines (2,300 milligrams per day). Whatever the
figure, which the public is blissfully ignorant of, a campaign to lower salt
intake has been in operation now for almost 50 years. Two recent papers have
looked at the pattern of salt intake in the US over that period.
Measuring salt intake in our diet is very difficult because,
over the short periods that dietary surveys are completed (1-4 days) salt
intake can fluctuate dramatically. An equally important limitation in this area
is the accuracy of food composition tables as to salt levels in foods. It
should be noted that over 80% of salt intake comes from foods and not the
saltcellar. Thus an alternative to measuring salt intake is to measure salt
excretion, specifically sodium excretion, since the body does not normally
accumulate sodium and thus the quantity excreted over 24 hours should roughly equal
the amount ingested over the same period.
Collecting all ones urine over a 24-hour period is very
difficult. The subjects have to carry a 5 liter plastic container with them
throughout the day and everywhere they go and they have to bring the container
to the bathroom to collect all of the urine excreted at each urinary event.
Thus, not surprisingly, such studies tend to have relatively small numbers.
Researchers at the Harvard School of Public Health searched the literature for
all studies that involved a 24-hour urinary sodium excretion measure among US
citizens over the period 1957 to 2003[1].
They found 38 studies. Of these, 5 were large with an average of 2,900 subjects
but the remaining 33 were relatively small with an average of <400 subjects
per study. The average daily output of sodium in milligrams per 24 hours was 3,526
prior to 1980, 3,418 across the ‘80s, 3,499 across the ‘90s and 3,849 post-2000.
Thus over the 40 years from the 1970’s, there was no significant change in
daily sodium excretion and the estimated average daily intake of sodium was 3,526
milligrams per day, well above any of the dietary guidelines issued.
Recently, another study on trends in sodium excretion was
published in which a single urine sample (“spot” urine sample) was used to
extrapolate to a 24-hour sodium excretion using adjustment equations set about
by an international research consortium called INTERSALT. In this study, they
used random samples from the US National Dietary Surveys[2]. Overall, they also found no change in sodium
excretion over the period 1988 to 2010 (3,160 mg/d for 1988-1994, 3,290mg/d for
2003-2006 and 3,290 for 2010). This equated to a daily sodium intake of 3,317
milligrams per day, which is very close to what the Harvard researchers found.
What do we take from these findings of a complete resistance
to change in sodium intakes? Reducing sodium in the human food chain is quite
different to reducing the levels of fat or sugar (the other two so-called “evils” of modern food). There are techniques
and technological solutions, which allow sugar intake to be reduced without a
loss of sweetness and also for fat reduction without the loss of the mouth feel
of fat. That is not the case for salt. If the level of salt intake is reduced
in breads it needs to be done over a long period so that consumers slowly adapt
their palate to lower salt levels. There
is no adequate sodium alternative.
There is a second way to look at these data. According to the
Darth Vaders of public health nutrition who would protect us all from the
inferior aspects of the modern diet, the
food industry has dramatically manipulated salt, fat and sugar levels in foods
over the last 40 years to manipulate our palate and their sales. As Michael
Pollan put it in his book “In Defense of Food”:
“Today foods are
processed in ways specifically designed to sell us more food by pushing our
evolutionary buttons-our inborn preferences for sweetness and fat and salt”.
If salt intake hasn’t changed between the early 70’s and
today, a 40-year period, then, has the food industry failed in their attempts
to push our evolutionary button for salt preference? To me, the most likely
explanation is very simple. Those who promulgate a food conspiracy, do so
without addressing the available evidence on food and nutrient intake patterns,
which should guide their thinking. But regrettably, when individuals set our
their stance on some issue of science, it is rarely for changing, whatever the
data might say.
