Salt

Salt is a chemical compound that combines the elements sodium and chloride. Sodium is the principal cation (a positively charged ion) of the circulating blood and tissue fluids of animals. Normal sodium content is needed to maintain the correct volume of these fluids and the chemical balance of the body. Sodium also helps with the absorption of glucose in the small intestine and in the conduction of nerve impulses.

Sodium levels are mainly regulated by the kidneys. If sodium levels are too low, the hormone aldosterone is released and this increases the amount of sodium held by the kidneys. On the other hand, if your body's salt levels become to high, you begin to feel thirsty and this is how your body maintains the right balance between the amount of water and sodium in the body.

The recommended dietary intake (RDI) for sodium is 920 to 2300mg per day Australians consume on average about two times the RDI. About 75% comes from processed foods, 15% from personal use at the table/cooking and <10% from fruit, vegetables and meat. All Australians are being asked to moderate their salt intake as a public health measure.

Salt loss is rare but can be dangerous
The body loses salt through urine, perspiration, vomiting and diarrhoea. If too much salt is lost, then the level of fluid in the blood will also drop. In severe cases, low sodium levels in the body can lead to:
· Muscle cramps
· Nausea
· Vomiting
· Dizziness.

Eventually lack of salt can lead to shock, coma and death. With the exception of acute gastroenteritis or severe sweating, sodium depletion is very unlikely because our diets contain more than enough salt and almost all dietary sodium is absorbed by the body. Many foods naturally contain traces of sodium, while processed foods tend to be loaded with salt.

The link with high blood pressure

The scientific literature relating sodium intake to blood pressure is extensive and dates back more than 100 years. High blood pressure, or hypertension, means that your blood is pumping harder than normal through your arteries. This condition is a risk factor in many illnesses, such as heart attack and stroke. The risk of stroke rises with every increment of diastolic pressure above 70mmHg. Hypertension is common but often without any noticeable symptoms. This means most people don't even realise they have it. Too much salt in the diet has been linked to high blood pressure. The extent to which sodium restriction lowers blood pressure is generally agreed to depend on age, initial blood pressure and degree of over weight - it is greater with age, in the more overweight and at higher blood pressures. Also, the effect of sodium restriction may not be seen for at least 5 weeks. Sodium restriction may not lower blood pressure further if blood pressure is within the nomal range. The exact mechanism is unclear, but it is thought that the excess salt increases the blood's fluid volume.

It is believed that genetic factors are also involved. About 90 per cent of Australians will experience some rise in blood pressure by the age of 65 to 69. Most doctors recommend a low salt diet if you have high blood pressure; however, the most effective dietary treatment for hypertension is weight loss. A meta-analysis of 56 trials concluded (Midgley et al JAMA 1996; 275: 1590-97) "dietary sodium restriction for older hypertensive individuals might be considered, but the evidence in the normotensive population does not support current recommendations for universal dietary sodium restriction".
This does not mean, however, that the RDI for soidum can be safely ignored.

Sodium intake and other health conditions

Excessive sodium intake has also been linked with other health conditions apart from raised blood pressure. They include any condition exacerbated by water retention.
Heart failure
Liver cirrhosis
Kidney problems and kidney stones
Oedema
Stroke
Gastric cancer
Left ventricular hypertrophy
Osteoporosis

Salt and calcium loss
Excessive salt intake increases the amount of calcium excreted in the urine. This may contribute to osteoporosis and increased risk of fracture. This effect is also seen in a high protein diet.

Sweating and salt replacement
It was once commonly believed that salt had to be replaced during hot weather or strenuous exercise, or else muscle cramps would result. The human body can happily survive on just one gram of sodium per day. Special hormones keep a constant check on sodium levels and can make adjustments for hot weather. Considering the typical Western diet, a genuine sodium shortage brought on through hot weather or exercise would be extremely rare, even among hard working athletes. The muscle cramps that sometimes follow a bout of profuse sweating are due to dehydration, not insufficient sodium. To prevent cramps, drink plenty of water on hot days and before, during and after exercise. This will also help to even out the water-sodium ratio in the body.

The sodium-potassium interaction
Our bodies are not designed physiologically for a high salt diet. We are designed for a high potassium diet. The hunter-gatherer diet was very high in potassium and low in sodium. This protected people from many illnesses which affect people who eat a modern Western diet. Today's Western diet is low in potassium and high in salt. Potassium is very protective and lowers blood pressure. Food processing tends to lower the potassium levels in many foods while increasing the sodium content. As such, it is better to consume unprocessed foods, such as fruit and vegetables, and wholegrain breads and cereals. Milling and polishing to make white rice and white flour from brown rice and wheat removes up to 70% of the K. Steaming, microwaving, stir-frying, baking/roasting and casseroling vegetables conserve potassium as opposed to boiling.

The palate adapts to a lower salt intake, and a failure of adaptation in old age has not been reported (Bertino et al., AJCN 1982; 36:1134-44).

Foods containing high amounts of salt

Did you know that:

1. A jam sandwich has only 30% less salt that a vegemite sandwich because most of the salt comes from the bread.
2. Onion/Celery/Garlic salts are not low sodium substitutes.
3. If you get rid of the salt shaker from your table and stop adding salt to cooking, this will only cut salt intake by about 15% for most people because the bulk of our salt intake comes from processed foods, especially bread.
4. A bowl of cornflakes has about the same salt as a small packet of plain chips.
5. Some sweet biscuits contain as much or more salt than savoury biscuits.
6. Of the fatty spreads, mayonnaise has the most salt (240mg/100g), followed by margarine (140mg), butter (130mg), dairy blends (110mg) and cream cheese (85mg/100g).
7. Ricotta, cottage, mozzarella and Swiss cheeses are lower in salt than most other cheeses; processed cheeses contain much more salt than regular cheeses.

Experts recommend that we reduce the amount of salt in our diet. Some people believe that sea salt is a healthier alternative to normal table salt, but both are made from sodium and chloride. However, sea salt contains iodine, which is needed for the proper functioning of the thyroid gland. Switching to sea salt or iodised salt can be helpful if your diet is iodine deficient (e.g if you don't eat fish once a week), but it won't reduce your sodium intake.

Switch to low salt bread
In general, processed foods contain the most salt, while unprocessed foods have the least amount. Bread is a major source of sodium in the diet contributing around 400-725mg/100g. Salt-reduced bread has about 345mg/100g - this still has three times too much salt to comply with the definition of a low salt food. Some salt-reduced breads in Australia include Pritikin and Burgen breads. In Europe (e.g. rural Tuscany in Italy), low salt bread is widely available (<120mg/100g).

The dietary guideline to eat plenty of bread jeopardises the RDI for sodium by leaving little room for other foods with a significant sodium content. Many food guides recommend we 'eat most' of bread and other cereals compared to other food groups and advise to avoid adding salt to our food - this is a paradox and of doubtful relevance when a single staple food is recommended in large quantities and which contributes so much salt in its present form. Switching to a low salt bread will have a significant effect on reducing sodium intake. A vegemite sandwich, for example, has more salt in the bread than in the vegemite.
Other cereal foods can mask the flavour of high concentrations of salt in the same remarkable manner e.g. Weetbix 280mg/100g. Lite-Bix 20mg/100g, Just Right 49mg/100g.

Foods that naturally contain traces of sodium include:
· Whole grains Cereals
· Meat
· Dairy products (milk contains a little more than average).

The current Food Standards Code states that a low salt food has a level of less than 120mg/100g (* 52 mmol/kg). Silverbeet, celery, kidneys, eggs have <200mg/100g (<87mmol/kg). The Heart Foundation tick implies that the food meets all the Dietary Guidelines, indeed the Heart Foundation makes that explicit claim. Very few foods meet all the Guidelines simultaneously, and the 'Tick' can be found on some very high-salt foods, including a low fat mayonnaise with a Na content of 1098mg/100g and a reduced fat processed cheese with 1500mg/100g.

Avoid processed foods
High salt foods that should be eaten sparingly include:
· Most fast foods, such as pizza.
· Most snack foods, such as potato chips.
· Processed meats, such as sausages, hot dogs and luncheon meats.
· Canned vegetables.
· Dehydrated or packet foods, such as instant pasta or soups.
· Prepackaged sauces and condiments, such as tomato sauce and soy sauce, and processed tomato products in general.
· White bread and bread rolls.

Salt added to food at the table versus salt added to cooking
Beauchamp (JAMA 1987; 258: 3275-78) was able to show that on low salt meals subjects sprinked far more salt (as would be expected). However, despite explicit pressure to use as much salt as they liked, they used only a fraction of the amount needed to restore the total Na content of ordinary (high salt) meals (about 130mml/d), and their Na excretion remained well within the RDI. The explanation offered by Beauchamp is that salt added at the table remains on the surface of the food and is nearly all tasted, whereas much of the salt used in cooking is not tasted (an example being the difficulty of detecting much of the heavy salt load in bread). The choice of low salt unprocessed foods makes a considerable difference even when salt is sprinkled liberally.

Iodised Salt
Our bodies need iodine (found in foods as iodide) for normal functioning of the thyroid gland and associated hormones. These two hormones regulate metabolic rate and promote growth and development throughout the body including the brain. If there is a deficiency of thyroid hormones in the blood, the thyroid gland enlarges and becomes what is known as goitre. Aside from resulting in goitre, iodine deficiency can lead to dry skin, hair loss, fatigue, and slowed reflexes. Iodine deficiency is especially serious in the developing fetus and young child. In the early years of life iodine deficiency can result in stunted growth, diminished intelligence, and retardation (commonly referred to as cretinism). Low levels of dietary iodine were thought to be an historic problem, or one of developing countries only. However, some researchers suspect that iodine intakes in Australia have dropped considerably, perhaps as much as half, over the past few decades. Many of the research studies conducted were small and localised, but indicate a need for further investigation. Some of the reasons iodine intake may have dropped in the Australian population include:

· Reduced use of salt in cooking and at the table (particularly iodised salt),
· Consuming most salt in processed foods, which as far as is known, is uniodised,
· Lower levels of iodine in milk due to changes in processing techniques.
· Iodine levels in Australian soils may have dropped?

For those people currently consuming a low salt diet, it may be beneficial to eat some type of seafood each week to ensure adequate iodine levels. This is especially relevant to pregnant women, due to the risk of intellectual disability for the child. Vegetarians or people who do not eat seafood can get iodine from seaweed or iodised salt.

Reduce your salt intake slowly
If your taste buds are used to salty foods, cutting back suddenly will probably lead to a relapse, simply because meals will taste too bland. Instead, make gradual adjustments. This also gives your body a chance to get used to the lower sodium intake and your body will then respond to less sodium. Reducing your sodium intake also increases your potassium intake. Some suggestions on how to reduce salt in your daily diet include:
Prefer reduced salt bread
Avoid high salt foods or eat them only occasionally.
Cut back on processed foods.
Cut back on takeaway and fast foods.
Buy fresh vegetables rather than canned.
Buy 'low salt' or 'salt free' versions of commercial sauces, such as tomato or soy sauces.
Since less than 20% of our salt intake comes from the salt we add directly to our food, it is OK to sprinkle a little iodised salt on nutritious foods to help us eat them
Instead of cooking with salt, just put a little on your food afterwards. This way you will get the taste, but use less salt because the salt is on the surface of the food instead of cooked into it.
Prefer iodised salt, especially if you do not eat seafood or if you are vegetarian
Try experimenting with herbs and spices such as garlic, oregano and lemon juice to add flavour to meals.

See also: 

a good on-line summary written by Choice Magazine June 2000 "Salt - should you cut down." 

Brochure on salt written by Rosemary Stanton: http://www.woolworths.com.au/dietinfo/rsa28.asp

Article co-authored by Better Health Channel
(Australian -Victorian Government website)

Last Updated: March 28, 2001s