Nanny Motsoaledi’s unscientific war on salt
- Ivo Vegter
- 04 Jul 2016 10:24 (South Africa)
At the beginning of July, new salt content regulations came into effect, after a three-year implementation period. By order of the health minister, Aaron Motsoaledi, a range of processed foods, including bread, butter, margarine, salted snacks, meats, soups, stock, gravy and noodles, will contain lower levels of salt. The limits will be reduced even further in 2019. In doing so, South Africa becomes one of the first countries in the world to regulate salt intake, rather than simply publishing dietary guidelines or agreeing voluntary salt content restrictions with the food industry.
The ostensible goal is to make it easier for South Africans to meet the adult dietary salt guidelines of the World Health Organisation (WHO), which stands at 5g per day. The problem is that the science on the subject is ambiguous, and far more complex than a simplistic and low daily recommended limit would suggest.
The theory that salt is implicated in high blood pressure dates back to anecdotal observations in 1904, according to a 2011 feature on the subject in Scientific American, entitled It’s Time to End the War on Salt. In the 1970s, a study in which rats were fed quantities of salt equivalent to half a kilo per day in humans found that this induced high blood pressure in the animals. This is not surprising. Being kept in a cage and force-fed such an extraordinary amount of salt by mad scientists in white coats would give me high blood pressure too.
The same researcher found correlations between populations with high salt intake and their incidence of high blood pressure and strokes. But critically, this correlation was not found within populations, suggesting that other factors were at play.
This is a common problem in the science of nutrition. It is hard to pin health outcomes on specific dietary ingredients or quantities, because humans differ in their nutritional needs, dietary habits, exercise regimes, water consumption and health status. People also differ significantly from the animals on which laboratory experiments are conducted. Confounding the issue even more, most human studies rely on self-reported food intake, which is known to be unreliable, especially when test subjects are instructed to modify their eating behaviour according to a strict diet.
It is silly to expect a single dietary guideline to apply to everyone from healthy, fit, young people, to the old and infirm. Worse, it can actually be dangerous to impose such limits by law.
The association between salt intake and high blood pressure became one of those “scientific consensus” matters that few questioned, despite the fact that the science on the subject was limited and inconclusive. The largest-ever study into the matter, the 52-population Intersalt study of 1988, proved to be fatally weak. The removal of only four outliers turned the positive correlation between salt intake and blood pressure into a negative one: more salt implied lower, not higher, blood pressure, except in a few very unusual groups of people. Clearly, the association was not as clear-cut as first assumed.
A number of recent studies cast further doubt on the simplistic view that more dietary salt leads to higher blood pressure, and therefore, that less salt will result in better health outcomes. A major meta-analysis of the scientific literature, published in the American Journal of Hypertension in 2014, found that randomised controlled trials in healthy human populations did not even exist. Dietary salt recommendations were being derived from studies in people who already suffer from cardio-vascular disease, high blood pressure or other health problems.
The studies that do exist suggest that both low-salt and high-salt diets are associated with increased mortality in those who already suffer from conditions that predispose them to ill health. The authors describe this as “a U-shaped association between sodium (salt) intake and health outcomes,” and recommend a daily intake of between 6.6 and 12.4 grams of salt per day. (If you click through to the study, note that it reports grams of sodium, which needs to be multiplied by 2.5 to get equivalent grams of salt.)
The healthy range recommended by these scientists, averaging 9.5 grams of salt a day, is much higher than the WHO guideline of less than 5g per day. In fact, it suggests that the WHO guideline is too low for good health. The idea that there is a lower limit and that too little salt can also be harmful is rarely spelled out in health information about dietary salt. Salt-reduction regulations aimed at reaching the WHO guideline certainly does not take it into account.
Another analysis of multiple studies, published in the same journal in 2011, found that the association between dietary salt reduction and blood pressure is small, and found no strong evidence that salt reduction had any effect on cardio-vascular disease incidence in people with normal blood pressure. Even in those with high blood pressure, there was no strong evidence that eating less salt had significant benefits. In addition, salt restriction actually increases your risk of dying if you have a dicky ticker. Putting people with heart disease at risk seems unwise in regulations that will affect the general population.
Yet another study found that salt intake was not associated with blood pressure, in either males or females, after adjusting for factors like weight, alcohol consumption, fruit consumption, and age. In fact, body mass index was the main factor influencing blood pressure that people could control.
A feature of all these studies is that they express uncertainty about study results, which is not reflected in the pronouncements of government regulators, medical groups, or lobbyists such as the Heart and Stroke Foundation of South Africa. This group simply says, “Salt is killing South Africans and it’s time to take action,” which is authoritarian policy based on hyperbole, not science.
The organisation cites the estimates of unnamed experts to the effect that salt intake by some South Africans could be as high as 40g of salt per day. The vague language means that if only two people eat that much salt, their claim would be technically true. However, this number is much higher than the global average salt consumption of 9g per day. If you’re going to advocate expensive government intervention, an average is a much more useful (and honest) number than an estimated maximum.
Other sources estimate that South Africans consume between two and three times the recommended daily allowance of salt. If this is true, that puts the average right around the high end of the safe salt intake range cited above, and suggests that onerous government intervention is not justified.
How the body processes salt is complex. Omitted from the simplistic salt-as-villain narrative is the inconvenient fact that there is a connection between salt (or rather, sodium) intake and another electrolyte, potassium. Potassium is available from sources such as citrus juices, bananas, avocados, potatoes, tomatoes, beans, fish and meat. South Africans’ potassium intake is generally believed to be below dietary guidelines, but a higher intake of potassium is known to reduce the effect of higher sodium intake. More specifically, an analysis of a more recent study than Intersalt, known as Trials of Hypertension Prevention, suggests that measuring only sodium intake is insufficient. What really matters to cardio-vascular disease risk is the ratio between sodium and potassium, not the absolute amounts of each. The higher the ratio, the worse it gets.
A major consequence of regulation that places restrictions on food ingredients is that it raises the cost of food. To meet the new standards, manufacturers need to develop new formulae with alternative ingredients to ensure palatability. The cost of doing so will be passed on to the consumer, as always. Should they not do so, this will not only place them at a competitive disadvantage, but it could affect the calorie intake of poor consumers who cannot afford tastier, more expensive food.
The latest science does not support a broad-stroke policy of salt reduction in processed foods. There is no evidence that moderate salt intake is bad for you, and eating too little salt is just as unhealthy as eating too much. The ratio of salt to sources of potassium is more important than salt intake alone, which suggests variety is more important than simple salt reduction. Healthy levels of salt will vary depending on people’s lifestyle and health condition. Lower salt content could reduce the palatability of food for the poor.
Current evidence suggests that the WHO’s dietary guideline of 5g per day, which South Africa is enshrining into regulation, is too low for a healthy diet, and people can easily eat twice as much salt without any adverse effects. In fact, the global average salt intake of 9g is almost twice as much, and just below the average suggested as healthy by the latest science. This suggests that people are naturally inclined to eat just enough salt for their bodies’ needs, without any intervention from government nannies.
Dietary advice from trusted sources is always welcome, if only to help consumers cut through the mountains of popular nutrition drivel that’s out there. But there is no justification whatsoever for restrictive, expensive, and authoritarian interference in people’s salt consumption. It would be a much greater benefit to public health to simply advise people what a varied diet looks like, and recommend that they eat everything in moderation. Unlike with salt, there would be plenty good evidence on which to base such advice.
This is not the first time that the Department of Health has burdened the people with unscientific rules and baseless regulations, and I’m sure it won’t be the last. But that doesn’t make it right. DM