Food for thought: Is eating salt bad?
What is salt?
Salt is a mineral made of sodium ions (chemical symbol: Na) and chloride ions (chemical symbol: Cl) that together form sodium chloride (NaCl), the major ingredient of the salt we put on our food. Salt is the main source of sodium in our diet.
Sodium helps us absorb our food, regulates our blood pressure and allows our nervous system to work correctly. Saltiness is one of the five tastes that our tongue can detect (along with bitterness, sweetness, sourness and umami). Contrary to popular belief, there are not specific regions of the tongue that recognise individual tastes; however, some areas are more sensitive to particular tastes than others.
Why add salt to food?
Salt has several vital roles in the food we eat: preserving it, enhancing its flavour or making its texture more palatable. Salt helps food to taste better by binding to water, preventing flavour compounds being dissolved and making them more likely to be picked up by the taste buds.
Adding the right amount of salt to foods prevents the growth of bacteria and fungi. These microscopic organisms can cause food to spoil and become inedible or dangerous to eat, but salt forces water to leave the bacterial or fungal cells, causing them to burst.
Salt is important for food texture, particularly in the meat industry. By injecting meat with a mixture of water, salt and phosphate, food producers can artificially increase its tenderness. It is believed that the chloride ions bind to the meat's muscle fibres and increase the space between them. This means more water molecules are able to fit into the space, making the meat more tender. The addition of phosphate means that less salt is needed to achieve the same effect.
Which foods contain salt?
Most of us are used to adding salt to our chips, but - perhaps surprisingly - salt we add ourselves is just a small proportion of the total we eat: some 75 per cent comes in the processed foods we buy.
It’s easy to identify some very salty foods (like bacon or crisps) by their taste, but there are others that you might not immediately think of as being high in salt, including bread and breakfast cereals. Even sweet foods like cakes can contain high levels of salt.
How much should we be eating?
Guidelines for the UK suggest that adults should eat no more than six grams of salt a day - about a teaspoonful. For children and babies, the levels are much lower. Sometimes food labels don’t list the amount of salt present but the amount of sodium. Chloride ions have a higher mass than sodium ions, so if you are given the amount of sodium present, multiply it by 2.5 to get the amount of salt.
How much are we eating?
On average, we eat too much salt - adults in the UK eat around 8.6 grams of salt a day. In 2004 the Food Standards Agency (FSA) introduced a public awareness campaign to encourage UK consumers to reduce their salt intake. This has seen salt intake drop from an average of 9.5 grams per person per day in 2003 to 8.6 grams per person per day.
Why is too much salt bad for our health?
Sodium is important for regulating our blood pressure, but having too much in our blood causes our kidneys to retain water in an attempt to dilute the extra sodium; this extra water raises the pressure within our arteries. According to the World Health Organization, 62 per cent of all strokes and 49 per cent of all coronary heart disease is attributable to high blood pressure (hypertension). People with high blood pressure often don’t know they have it, as it can be a symptomless disease. A large salt intake is not the only cause of high blood pressure, and other lifestyle factors - such as smoking or a lack of exercise - can contribute to the problem.
Can we adapt to lower salt in our diet?
We’ve learnt that salt is in almost all the processed food we buy, and we’re used to adding it ourselves before we eat. Are we addicted to it? Although there is no definitive research showing this to be true in humans, studies in rats on a low-salt diet show that salt may possess addictive qualities, with the rats exhibiting symptoms seen following drug withdrawal.
To stay healthy, we only need a fraction of the salt we eat - some 0.5 grams of salt per day. Not adding extra salt to the food you cook is a good start to reducing salt levels, as is choosing foods that are lower in salt. Foods high in salt tend to have more than 1.5 grams of salt per 100 grams, while foods considered low in salt have 0.3 grams or less.
Although salt is important for taste, levels can be reduced in many foods without us even realising. For instance, white bread can have up to 25 per cent of its salt removed without adversely affecting flavour. Reducing the amount of salt we eat can make our food taste bland at first, but - over time - we can adapt to this, and food should taste just as pleasant a few months later.
Is the food industry trying to lower salt levels?
In 2006, the FSA published voluntary targets for reducing salt in pre-prepared food. As a result, many popular food items have seen their salt levels lowered. For example, a reduction of around 44 per cent has been seen in several branded breakfast cereals and a reduction of 32 per cent has been seen in some brands of crisps.
Lowering levels of salt in processed foods can be quite a challenge. The easiest way is to replace it with an alternative, such as potassium chloride (KCl). However, this may lead to food having a metallic taste, meaning additional chemicals are needed to hide this unpleasantness. Another alternative is to compensate for the lack of sodium chloride by adding additional herbs or spices. The numbers of patents for salt-reducing technologies has risen dramatically over the past few years, showing that food companies are searching for new ways to reduce salt levels in foods in response to governmental and consumer pressure.
Read more mythbusting around food online and on p12-13 of 'Big Picture: Food and Diet' magazine. You can order a copy or download a PDF.
Image: Salt (sodium chloride). Credit: Efraim Lev and Zohar Amar, Wellcome Images.
References
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This article is part of the online content for ‘Big Picture: Food and Diet’.