Researchers turf low-salt diet out
Controversial study shows association with increased risk of heart attacks, strokes and death even in patients suffering from high blood pressure, writes Marika Sboros
It is like pouring salt into an open scientific wound. A major new Canadian-led study says eating too little salt can be dangerous even for people whose blood pressure is high.
The findings go against conventional low-salt advice for all, regardless of blood pressure levels. The researchers have elicited strong reaction in the latest edition of the Lancet.
Lead author of the study published in the Lancet in July is epidemiology professor Dr Andrew Mente, of the Population Health Research Institute in Hamilton, Ontario. The study is a meta-analysis of data from 133,118 people – 63,559 with and 69,559 without hypertension – from 49 countries. The median age was 55.
The findings show an association between low-salt intake and increased risk of cardiovascular events (heart attack and stroke) and death in those with or without hypertension.
The researchers say doctors should target only advice to lower salt intake at hypertensive populations who are already eating high-sodium diets.
In other words, people really only need to eat less salt if they have hypertension and are eating a high-salt diet.
A Lancet editorial reads there is "no real disagreement" high salt intake is associated with hypertension, and hypertension is associated with more cardiovascular events. However, there is also "no agreement" on the level at which doctors consider salt intake to be high.
More worrying, the editorial reads evidence for benefit in recommended target levels of salt intake is "virtually absent".
There are no randomised controlled trials (the "gold standard" of research) measuring health outcomes with sodium intake less than 2.3g daily.
That is about 6g, or a teaspoon of salt.
Salt comprises sodium and chloride. Only 40% of salt’s weight is sodium. So one can always eat more salt than sodium in recommendations.
Mente’s study is not a randomised controlled trial, but the editorial reads its data is "as robust as data used to advocate reductions to low levels".
At the very least, this data should demand "re-evaluation of the wisdom of reducing levels of dietary salt without high-grade evidence to support such reductions", the study reads.
Evidence-based medicine has become the "bedrock of treatment guidelines", the editorial reads. However, "evidence-based medicine does not always translate into evidence-based policy", it continues.
The Heart and Stroke Foundation of SA follows the World Health Organisation (WHO) recommendation of 6g of salt daily.
Earlier this year, the foundation launched a lobby group, Salt Watch. Its mission statement: to encourage all South Africans to "eat less salt". The American Heart Association advises 1.5g of sodium or about 4g salt.
Low-salt is a pillar of official low-fat, high-carbohydrate dietary guidelines in the US and SA, that closely follows the US.
In the latest issue of the Lancet, American Heart Association president Dr Stephen Houser says studies showing harm from too little sodium have "methodological flaws".
These flaws "undermine their usefulness to guide public policy and population sodium-intake recommendations".
Houser says research shows that decreasing sodium in the food supply could save more than 500,000 lives in the US.
That translates into billions of dollars saved in health-care costs over the next decade.
"To us … that’s convincing evidence," he says.
In the same issue of the Lancet, New Zealand researchers led by Prof Grant Schofield, head of public health at Auckland University of Technology, come at the debate from a different angle.
With his colleagues George Henderson and the pharmacist DrCatherine Crofts, Schofield says the evidence base for salt advice has "limiting factors".
Researchers "consider salt independent of the dietary context in which people eat it".
They also don’t consider effects of metabolism on sodium regulation, he says.
Mente’s study prompted Schofield and colleagues to look at the influence of dietary content on hypertension risk. In particular, they looked at research on sodium reabsorption in the kidneys. They found several experiments linking it to glucose and insulin concentrations in the blood.
They say it is well accepted that "essential hypertension" – that is not secondary to another disease – is part of metabolic syndrome. That is along with high insulin, elevated blood sugar (glucose), high triglycerides (blood fats) and low HDL (high-density lipoprotein, the so-called "good cholesterol").
Research also shows that a major cause of insulin resistance and metabolic syndrome is a high-carbohydrate diet.
Schofield and colleagues say research into the link between salt intake and metabolic syndrome could bring scientists "a step closer to identifying the root cause of a pathology for which salt alone has historically borne an excessive share of the blame". They suggest that future salt surveys include the fasting-triglyceride-to-HDL-cholesterol ratio as "a proxy for a high insulin response indicating carbohydrate intolerance". In other words, doctors in future may advise one to reduce carbohydrate rather than salt intake.
Johannesburg cardiologist Dr Riaz Motara says multiple factors are involved in hypertension and cardiovascular risk.
"The question is not just that too much salt is bad," he says.
People who eat Western-style diets are eating too much salt, partly because it is hidden in highly refined, processed foods. However, they are also eating excessive sugar and starches in these foods. That is a big problem for blood pressure, hearts and brains, Motara says.
Before 1950 in the US, people consumed around 2kg sugar per year on average. These days, they are eating a whopping 60kg to 80kg of sugars and other carbohydrate foods, Motara says. Lots of these foods are devoid of micronutrients.
In the past 50 years, there has been a drastic rise in cardiovascular disease, cancer and autoimmune diseases in many countries including SA, he says.
"The biggest lie we’ve been told is that we need to eat low-fat or fat-free food," Motara says. Any product that is low in fat is high in something else, he says. That something is usually refined sugar.
"Sugar has become an addiction. It’s why we are now sitting with an epidemic of adult and childhood obesity in South Africa," he says.
"We have also changed the way we grow and harvest fruit and vegetables," he adds.
Another problem is excess intake of pro-inflammatory omega-6 fats. Common sources are grain-fed meats and vegetable (seed) oils, such as sunflower and canola, Motara says. These raise cholesterol and blood pressure and increase the risk of diabetes, heart attack and stroke, he says.
That is the problem, but what about the solution?
"Primordial prevention," says Motara. "Health department and government strategies should look at what people are and are not eating.
"They must also look at what nutrition people are not getting that is contributing to the increased risk of cardiovascular disease," he says.
Ideally, people should eat a "traditional diet".
By that, Motara means one that is higher-fat, medium-protein and low in carbohydrate.
Fat is more satiating than protein or carbohydrate, Motara says. Not just any fat will do.
Most people need to increase their intake of foods rich in omega-3 fats, preferably organic. Good sources are lamb, pasture-fed animals and game meats such as ostrich.
South African-born cardiologist Dr Dennis Goodman is clinical professor of medicine at New York University’s Department of Cardiology and Preventative Medicine. He is also director of Integrative Medicine at New York School of Medicine.
As a clinician, Goodman says he tries to keep advice simple. He strongly recommends a low-salt diet to patients with hypertension because many of them are salt-sensitive.
"We need some salt in our diet," Goodman says. "I recommend using sea salt and avoiding table salt (sodium chloride)."