Salt …

It’s been traded, taxed, fought over. It’s been ploughed into the fields of defeated city states. It is used in some religious ceremonies. It is essential to life and one of the fundamental tastes mediated by the human tongue. It’s the difference between a herring and a kipper, pork and bacon because it is an effective preservative.  It has been used as currency and it gives us the word salary (although the Roman Army was never paid in salt).

Solntsata in Bulgaria was possibly the first city in Europe. The name translates as salt works and they have been in use since 5400 BC. There is evidence of even older salt extraction processes in China.

Cheetham Saltworks, Victoria

It is essential to our physiology, without it we couldn’t even generate a nerve impulse. But In excess it increases blood pressure which in turn increases the risk of heart disease and stroke. So how much is the right much?

The Australian guidelines are formulated by the National Health and Medical Research Council and can be accessed at this government website which also sets out the logic behind the recommendations. They deal in milligrams of sodium. Salt is sodium chloride. 1 unit of sodium = approximately 2.5 units of salt once you add the chloride.

The suggested daily target is 2 grams of sodium a day for adults (roughly 5 grams of salt). The NH&MRC wrestled with an upper limit but concluded that

…  because the relationship between sodium intake and blood pressure is progressive and continuous, it is difficult to set a UL precisely.

So no upper limit was set.

The average Australian is ingesting about 9 grams of salt a day currently. Some is an inescapable part of the raw ingredients of our diet but much of that figure is added to restaurant and take away food, processed and packaged food, and drinks such as Coca Cola and sports drinks. It makes food more palatable by dialing down the sensations of bitterness and over sweetness. In the case of drinks it increases thirst – how convenient for the manufacturers.

So far as it goes the NH&MRC guideline purports to have an evidence base, is easy to understand and is aimed at getting the community’s blood pressure down.

The low carb intelligentsia seem to give the issue very little concern. How come?

A low carb diet has a real food base. McDonalds is out. Most packaged foods are out. If you start with the raw ingredients of a keto diet the challenge is to get enough salt especially if you are also into sweaty exercise.

The phrase lower limit doesn’t occur in the government website. Whilst the essential nature of salt is acknowledged the assumption seems to be that less is best. There is evidence to the contrary.

An article by Mente and an insane number of other authors (28 other authors – I imagine they wrote every 29th word and then had a committee meeting on where to put the punctuation marks) )from the Lancet May 2016 entitled Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: A pooled analysis of data from four studies, reports on a study of 133,118 individuals roughly half of whom were hypertensive. The daily intake of salt was compared to the likelihood of death and major cardiovascular events and blood pressure over a median period of 4.2 years.

Compared with moderate sodium intake, high sodium intake is associated with an increased risk of cardiovascular events and death in hypertensive populations (no association in normotensive population), while the association of low sodium intake with increased risk of cardiovascular events and death is observed in those with or without hypertension.

There is a subtlety there that I will return to but first let’s take a look at the results as a graph …

On the vertical axis we have the hazard ratio, on the horizontal axis the daily excretion of sodium in mg. Daily excretion of sodium is pretty much the same thing as daily intake of sodium. The amount of  sodium in blood is regulated by the kidneys and there is no storage mechanism. The U-shaped curve comes as no surprise, sodium is essential therefore as you reduce the intake you’d expect to reach a point where risk starts to increase. Excretion of less than 3g of sodium a day increases the risk of cardiovascular catastrophes and death. The graph shows that the risk increases above 7g a day. The lowest point of the curve falls between 4000 mg and 6000mg of sodium or ~11 grams of salt.

If instead of looking at the whole cohort we look at the hypertensive and normotensive subgroups steepness to the left of the low point stays the same for both but to the right it rises more steeply for those with high blood pressure. Why should this be?

The kidneys play a pivotal role in the maintenance of blood pressure and not all kidneys are equal. Researchers have bred salt sensitive rats that develop high blood pressure. If their kidneys are transplanted into normal rats the recipients develop high blood pressure on a high sodium diet. Normal rats receiving kidneys from normal rats do far better. The problem follows the kidney. This is borne out in human transplantation as well. If the donor has a family history of hypertension the recipient has a ten fold increased risk of developing hypertension.

Mente et al looks like a pretty robust study. If we accept their findings it follows that –

  • The Australian public are not far from an ideal salt intake.
  • The NH&MRC guidelines are set at a level which will increase risk.
  • and unless you have hypertension there are more important things to think about.

If only things were that easy. Not all studies bear this out. Cook et al

found an increased risk at high sodium intake and a direct relation with total mortality even at the lowest levels of sodium intake.

They suggest that other studies are in error …

While several studies suggest beneficial effects of lower sodium on cardiovascular disease, the relationship with total mortality remains controversial. Some have reported a J-shaped curve, but this may be due to poor quality measurement of sodium or confounding bias.

Clearly the definitive answer still eludes us although I am suspicious of any study of an essential nutrient that doesn’t find detriment at a low level of intake.

Which study do we choose to ignore?

I think the best strategy is to ignore neither despite their contradiction. Rather we should take our blood pressure. It’s easily done at home. The hypothetical guy I studied in Physiology weighed 74kg had a pulse rate of 72 and a BP of 120/80. Blood pressure tends to rise through life and the doctor tends to reach for his prescription pad at about 140/90. If you’re border line and want to stave off the pills there are some non-drug remedies to consider …

  • Lose weight
  • Exercise
  • Reduce your salt intake

If you’ve got it to lose then 10 kg off should drop your BP by about 10 mm of mercury. For each gram reduction of salt a hypertensive person can hope to drop about 2 mm of mercury.

Metabolic Syndrome …

  • High blood pressure
  • High blood glucose
  • Excess fat around the waist
  • Raised cholesterol
  • Raised triglycerides

If you have any three of these you are in the gun. Your risks of type 2 diabetes and heart disease are higher.

Syndromes are not diseases they are clusters of signs that have a high chance of occurring together. Presumably there is an underlying cause but it may not be obvious. In this instance, though, your money would be pretty safe on insulin resistance.

According to the Mayo Clinic website if you have any one of these it’s time to see your doctor. They go on to say …

  • Metabolic syndrome is increasingly common, and up to one-third of U.S. adults have it. If you have metabolic syndrome or any of its components, aggressive lifestyle changes can delay or even prevent the development of serious health problems.

My score is one out of five. I have seen the doctor. The aggressive life style change is underway. You didn’t think I was just writing this for your benefit, did you?

When I look in the bathroom mirror my belly doesn’t look too bad. If I turn my head 90 degrees to the right the awful truth is revealed in a mirror in the adjacent walk-in robe. I guess that’s why friends and the ever solicitous Gayle were so keen to get me on the bike. I’m sure they didn’t expect an instant cycling tragic.

I googled “ideal girth” and got the shock of my life. I was quite competitive though. That’s something you can checkout for yourself or leave a mystery.

I then googled “ideal waist size” and found what I wanted. Then I found a tape measure. And then I contemplated my future.

A man’s waist should be no greater than 40 inches or 102 cm. A woman’s should be no more than 35 inches or 89 cm. Oh, the shame … 44 inches.

Armed with that and your height you can get a reasonably close estimate of your percentage of body fat. The theory is <Here> a calculator can be found <Here>. It is a better measure than BMI which suffers from a number of deficiencies. Arnold Schwarzenegger at his peak had a BMI of 34 (or thereabouts, accounts vary). That puts him securely in the obese range (30 – 39.9). Doesn’t look it …

Actually my BMI ain’t that different. Should be OK.

Well no. It’s time for exercise and diet. Which diet?

Insulin …

Broadly speaking plants get their energy by converting sunshine into sugar. Animals have to eat. Either way the currency of energy is glucose. C₆H₁₂O₆. Burning it consumes oxygen and yields carbon dioxide, water and releases the means to cause muscle to contract, brains to think and all the other processes living things have to carry out.

And a lot of those processes are aimed at keeping the interior environment of the organism in a fairly constant state consistent with continued survival, a process called homeostasis. When a meal is ingested a very complex chain of events follows. To coordinate it all cells and organs need to communicate with each other and they do this by a number of means.

Think of a thermostat , a thermometer and a heater. At a certain temperature the the thermometer triggers a message that turns on the heater. The temperature rises. When it reaches another temperature the thermometer triggers another message that turns the heater off. The temperature stays within set limits and we have a simple example of a negative feed back loop.

Now magnify that many times over. The messages can travel by nerves or by chemicals. Some chemicals may not go far, some enter the circulation and have their effect remotely. Think about something delicious and you will prepare the pleasure centres of your brain for impending enjoyment and your salivary glands will get to work. This will intensify as you see it or smell it. Start chewing and your taste buds will bring more information to your brain’s attention. When your stomach begins to fill the distention will trigger an impulse  via the vagus nerve to tell the brain to think about stopping eating. The gut gets to work on digestion. Nutrients are absorbed, transported, processed and stored. All this has to happen without pushing the internal environment out of kilter. And feedback loops are working at every step of the way.

The number of chemical messengers is staggering. For a glimpse at how complex it all is try this <Paper> even if only to see how much I’ve simplified what comes next.

Among the chemicals at work there are some internet stars, Ghrelin, Leptin and Insulin among them.

When your tummy grumbles think of Ghrelin. It is mainly secreted by the stomach and acts mainly on the hypothalamus. Levels are high when fasting and as meal times approach. Injection of Ghrelin will stimulate the desire to eat. After your successful weight loss diet Ghrelin will help you put the weight back on.

Leptin on the other hand will help you stay the same weight. Leptin comes from happy fat cells, levels rise in obesity and fall during weight loss. If it’s allowed to do its job it triggers a complex series of events in the brain which suppress appetite.

Evolution came up with a system that prompted us to eat when energy was needed and stop when we’d eaten enough. It also had to permit storage of excess energy when available against the times when food was scarce. We store excess glucose by turning it into fat, we have no similar mechanism for storing excess protein. The diet that evolution got to work on for almost all of human existence was a hunter gatherer diet. Tubers, meat, fat, fruit in season and maybe honey once in a blue moon.

The agricultural revolution began about 12,000 years ago. Grains became much more prominent. Evolution continued to work and has made it possible for some of us to consume milk after infancy. Has it brought us to a point where we are as well in tune with our diet as we were before?

The industrial diet has seen sugar intake rise from negligible amounts to a point where we are eating almost our own weight of sugar a year. Our weight at the beginning of the year that is.

taken from unimedliving.

Processed food now consumes 22.9% of our food expenditure, more than all other categories with meat in second place.

Westerners are eating about a third more calories than we actually need.

This dietary change is recent. Evolution has had no time to hand a Darwin award to the unfit but it’s working on it. We are getting fat and we are getting sick (not necessarily both, some obese people are metabolically well).

We don’t like being fat, just look at the shelves in the book shop. We diet, we join the gym … and we fail. So if it’s not a hedonistic plunge into gluttony and sloth why are we in the midst of an epidemic of obesity, diabetes type 2, metabolic syndrome, cardiovascular disease, cancer and dementia?

Well obesity and diabetes are obviously related to what we put in our mouths. Could the culprit be the newly abundant refined carbohydrates we’ve added to our diet?

Sucrose is a molecule of glucose joined to a molecule of fructose. These are quickly split asunder in the gut and absorbed individually. Glucose can be metabolised by virtually every cell in the body. Fructose can only be metabolised in the liver. Glucose goes every which way, only a fraction ends up in the liver. All the fructose goes to the liver. Fructose is about twice as sweet as glucose.

In the liver spare glucose is stored as glycogen. Good stuff, ask any endurance athlete. Excess is exported for storage as fat. Bad stuff ask any endurance athlete. None of the fructose ends up as glycogen, if it’s not used immediately for energy it goes to fat. If the liver is swamped the fat doesn’t get exported fast enough. Now we have a fatty liver.

Fructose was present in our hunter gatherer diet. Our ancestors enjoyed fruit, it’s delicious and a rich source of energy. It was seasonal and in limited quantities, gorge on it now, store the energy for the lean times. It made good evolutionary sense. That was then, now we have fructose on demand, our livers are swimming in the stuff, every day. Not only in fruit, its in almost everything that comes in a packet or a bottle.

When sugars hit the bloodstream the pancreas sends out insulin. The job of insulin is to pack glucose away into cells. Muscle cells grab what they need and store it as glycogen. This will be used as fuel during muscle activity. There is no mechanism for getting it out again. Fat cells will store it as fat. This can be re-exported when needed but not while insulin levels are high. Other cells take what they need for energy.

The Leptin level is rising, blood glucose and insulin are coming down. The pleasure centres of the brain are buzzing. All is well with the world.

Soon the blood glucose is getting low again. We can leave it to our physiology to sort that out or we can have another soft drink, gee that was good. All too often our pleasure  centres  opt for the quick fix.

Over the years of repeated bursts of sugar our cells begin to be less responsive to insulin. The pancreas responds by making more. Glucose levels remain normal but fasting insulin levels are raised. This means that fat cells cannot export glucose. Raised insulin prevents Leptin delivering its message to the brain. Hunger now has the upper hand, fat utilisation has ceased, weight is going up.

A few years later the poor old pancreas will not be able to keep up. Insulin output drops,  blood glucose soars. This is now type 2 Diabetes.

By now the fat is surrounding your organs, your arteries are narrowing and stiffening. Your blood pressure is rising along with the risk of a heart attack or stroke.

Diabetes Australia recommends following the Australian Dietary Guidelines but eating little and often. Apart from some chocolate and the odd icecream isn’t that how we got into this mess? In time you will have to start injecting Insulin …

When insulin is required, it is important to understand that this is just the natural progression of the condition.

So just surrender.