The science of salt consumption

It is reported that not enough restaurants and fast food outlets are doing enough to reduce the amount of salt in their food.

I remember many years ago seeing a poster in a hospital about good eating habits.  It recommended eating at least five portions of fruit and vegetables every day, and it dawned on me that I often went for whole days at a time without eating any fruit or vegetables.  I have heard this dietary advice repeated many times, and eventually I became fastidious about my fruit consumption, and am still fairly fastidious to this day.

At some point - I cannot remember when - I became aware of advice about salt consumption. The advice is that men should consume no more than 6 grams of salt each day (or 7 grams, depending on who you believe); that women should consume no more than 5 grams of salt, and that children should consume no more than 3 grams.  What I do recall is that I did not give the matter any thought until one day I watched a television programme which stated that there is a gram of salt in a bowl of a popular brand of breakfast cereal.  I investigated, and was alarmed to find that I had probably been consuming far more than 6 grams of salt each day for as long as I could remember.

Another piece of advice we often hear is about alcohol consumption.  We are often told that men should drink no more than fourteen alcoholic drinks each week, with a lower limit for women.  I find these limits confusing, because it is based on an assumption of a standard alcoholic drink, but how many alcoholic drinks really are standard?  For example, beer is commonly served either by the pint or by the bottle.  Surely a pint of beer contains more alcohol than a bottle.

So far as I am aware, not one of these three recommendations is based on any actual science, in which case we are entitled to ask why they are often publicised as if they are.  We could argue that the recommendations make sense even if they are not strictly true.  We could argue that it makes sense to eat at least some fruit and vegetables every day, and that it makes sense not to drink too much alcohol.

Then again, most of us probably know at least one person who either is or used to be a heavy drinker, but who enjoys good health.  Likewise, most of us probably know at least one person who often goes for whole days at a time without eating any fruit or vegetables, but who enjoys good health.  In fact I used to be such a person.

The recommendation I find most bizarre is the one about salt consumption.  Do you know how much salt you consume each day?  The loaf of bread in my kitchen right now contains just 0.3 grams per slice, but I have known bread to contain as much as 0.7 grams of salt per slice.  That means that a child who eats just five slices of bread in a day might be exceeding the 3 grams limit.

Suppose a young boy eats a bowl of Frosties for breakfast along with two slices of buttered toast.  That alone probably equals at least 0.9g of salt, even if the butter is unsalted.  Add in the biscuits and crisps he will probably eat for a mid-morning snack, and any processed food such as pizzas that he will eat later in the day, and it is not too hard to imagine that there may not be one child in the whole country who consumes no more than 3 grams of salt in a typical day.  In fact many children in developed countries probably consume far more than 3 grams of salt pretty well every day.

It also appears likely that a lot of adults routinely exceed their supposed limits on salt consumption on a typical day, and yet we remain a fairly healthy country.  Some readers may be thinking that by eating too much salt we are not exposing ourselves to short term medical risks, but that we are nevertheless contributing to long term health problems, and it is absolutely true that we will all die one day.  As a nation we tend to live for many decades, and our hospital wards tend to be occupied mainly by people who are elderly.

In short, the recommendations on salt consumption are quite obviously a load of cobblers.

Where do these inaccurate recommendations come from?  I read once - I can’t remember where – that the recommendation that we should eat at least five portions of fruit and vegetables every day was originally a marketing gimmick by the fruit and vegetable industry.  I have no idea where the other two recommendations come from.

If you eat at least five portions of fruit and vegetables each day, then companies like Del Monte and Dole which sell fruit can hope to benefit as a result.  By contrast, if you consume less fruit and vegetables, then you will presumably eat more of other foods to compensate, but more of what exactly?  Biscuits?  Pasta?  Tinned pilchards?  It appears that no one in the food industry has any obvious incentive to persuade you not to eat at least five portions of fruit and vegetables each day.

There is therefore a simple logic to the fruit and vegetable recommendation.  Some people benefit from you believing it, but no one obviously stands to gain from you not believing it.  It is a very different story with the other two recommendations.

I am not sure that anyone obviously stands to gain from me being careful about my consumption of either salt or alcohol.  Can anyone put me right here?  Nevertheless there are a lot of companies which potentially gain from me not caring about how much salt or alcohol I consume, and many of those companies are not short of money.  Major brewing companies like Diageo (which makes Guinness) and Heineken would presumably have no trouble in employing scientists to argue that it is in fact safe to drink sixteen or even eighteen standard alcoholic drinks in a week.  Likewise, processed food companies like McVitie’s and Kellogg’s would presumably have no trouble in employing scientists to argue that it is in fact safe for a child to consume 4 grams of salt each day.

As with my previous essay on science, comments are invited.  If I’ve got anything wrong, then please let me know.

Update: since writing this, I have become aware of a major study into diet which suggests that eating up to five portions of fruit and vegetables in a day boosts longevity.  Nevertheless this is a recent study, whereas the advice itself has been widely publicised for many years now.  I may therefore be correct in assuming that the recommendation to eat five portions of fruit and vegetables each day was not founded on any science when it was first promulgated as truth. 

Another update: it is now reported that the average adult in the UK does not eat five portions a day.