Craving salt may not always be the manifestation of sodium depletion. Salt hunger in humans is partly psychological, and our brains can trick us into overdosing on salt.
Back in the days when we were a bunch of sparse-haired advanced apes walking on two legs eating fruits from trees, digging roots out of the soil and hunting a wild boar or two once in a while – salt or sodium was deficient in our diets.
Gradually we discovered salt as a separate ingredient and realised we have a hunger for it. Next we learnt to extract it from sea water and began to sprinkle it over anything we ate. Salt became a necessity and no food was complete without the perfect dash of saltiness. Even desserts require a pinch of salt for flavour enhancement.
Our current salt intake has reached a point where it is no longer healthy. In fact high salt intake in the modern human population is a leading cause for many chronic non-communicable diseases including cardiovascular diseases.
But how did we turn into such salt gluttons? Despite our surprisingly high sodium consumption we still suffer from salt cravings. Research finds that not all of it is physiological. A part of it is totally psychological. Our brain tricks us into eating more salty foods even when we have ample sodium in our systems.
Let’s understand the psychological workings behind our ridiculous salt cravings.
Sodium depletion drives salt hunger
Apart from food and water all animals have a specific appetite for salt. It is termed ‘salt hunger’ or ‘sodium appetite’.
Unlike other minerals Sodium is lost in large proportions from the body through sweat, urine and stool. However, our kidneys work full time to maintain normal sodium levels in our body by retaining or excreting sodium depending on our sodium consumption per day. Special circumstances like excessive sweating, diarrhoea, vomiting, pregnancy or maintaining a salt-free diet long-term can result in a sodium crisis. When a sodium deficiency in created in the body, it evokes our sodium appetite or salt hunger.
But sodium appetite depends largely on the usual diet of the animal. Carnivores do not display salt hunger because they get enough of it from the meat they consume. As such their nervous system did not learn to recognize salt hunger. On the other hand, for herbivores and omnivores, sodium is hard to come by in their normal diets. They have a specific hunger for sodium which exemplifies as salt craving. When deprived of sodium they look out for foods high in salt content for replenishment. You must have seen elephants and deer licking chunks of mineral rocks or moose getting down knee-deep in lakes when they are not frozen during the summer months to chomp on aquatic vegetation. Well, they are only satisfying their salt craving!
Similarly with early humans, when our diets ran low on sodium we actively searched for sodium rich food from our surroundings. Our nervous systems are built to identify sodium deficiency and our salt hunger drives us to consume more salty food to replenish our bodies with sodium.
However, this same sodium appetite is causing a bit of a disorder in our current state of affairs as now our diets have too much sodium. When our recommended sodium consumption per day is supposed to be just 500mg or a fourth of a teaspoon, most adults worldwide consume over 4000mg of sodium per day.
The hedonic side of salt cravings
Sodium depletion is the driving force behind salt cravings. When sodium levels drop below a certain mark it signals our central nervous system to intake more sodium. The outcome is an exhibition of preference for salty substances. This is called the hedonic shift.
There is a superb demonstration of this behaviour in laboratory rats. When they have enough sodium in their system they show aversive behaviour to saline water. But when sodium depleted they seek out the saline water and despite previous bad experiences with it they repeatedly press levers to obtain the saline solution. These rats also display rewarding behaviours after tasting the salty solution indicating that they have obtained pleasure from consuming salt.
During a salt deplete state, consuming salty food induces dopamine release in the brain. Thus, the taste of salt which under a salt replete state was deemed irksome is seen as pleasurable.
In an experiment when human subjects were sodium depleted, they preferred salty foods over unsalted food often tagging unsalted food as bland and tasteless even if they were rich with other flavours. Finding salty foods pleasurable after salt depletion is our nervous system telling us that we need to replenish our sodium levels.
No salt for too long can make you depressed
When the body is deprived of salt or sodium for a long time symptoms of depression shows up. It is called anhedonia, where stimuli and activities that normally evoke pleasure in the individual loses their pleasant nature.
Laboratory rats find sugar solution rewarding and would drink it out of pleasure even when they are not under any physiological need for sucrose. When sodium or salt deprived, these rats drink sugar solution less as they do not find it pleasurable anymore. In other words, the rats are depressed. When provided with saline solution, normalcy is restored and they find sugar solution enjoyable once again.
Something similar is at play for humans as well when we binge eat salty products under depression. We are only attempting to stimulate the reward centers of our brains to pull us out of depression.
Salt gluttony and salt sensitization
It has been observed that after two or more episodes of salt depletion our lifelong salt intake increases dramatically. The phenomenon is called salt sensitization. The mechanism behind it is said to be neural plasticity. After few episodes of salt depletion, permanent changes happen in the nervous system that increases our salt consumption for lifetime. It is linked to an elevation in expression of several mRNAs and other markers responsible for salt appetite.
However, salt depletion may not always be physiological. It can be psychological deprivation as well. When salt cravings are ignored and salt appetite is not satiated, the deprivation can be interpreted as salt depletion by our nervous system.
The modern cause of salt addiction
The main culprit to blame for the emergence of salt addiction are ultra-processed fast foods. Our systems evolved under salt deplete conditions where deficiency in sodium had to provide a strong impetus for us to head out and actually search for salt. But under current salt replete condition this physiological adaptation turned out to be an evolutionary misfit because our physiology could not keep pace with the fast cultural evolution in our lifestyle. There is a loophole in the neurological pathway which in being exploited to pump sodium into our systems.
Most processed foods are loaded with sodium and overwhelming to our taste buds too. Salt along with other palatable tastes activates (reduces neuron firing rate) the nucleus accumbens (NAc), the reward center located in our forebrain. It is the same region affected by euphoric drugs like opium. The results are a dopamine surge and a feeling of satisfaction.
The pleasurable sensation induces us to actively seek out salty foods and gradually increases the pleasure kick in limit so that we end up consuming more salty foods and hence calories with time. The outcome is similar to opiate and dopamine withdrawal. Obesity, over-eating, cardiac disorders and other diseases are the long-term results if not addressed on time.
Can salt cravings be managed?
Absolutely yes, once you are aware of how much salt you are consuming in a day and what physical activities you are involved in. If you are exercising and have sweated heavily, you definitely need to replenish all the salt lost in your sweat with a salty diet. Diarrhoea, vomiting and some other such scenarios need to be looked out for. Considerable amounts of electrolytes including sodium are lost in those conditions and must be replenished immediately. Or it may become a survival threat for the individual.
Binge eating and senseless consumption of processed foods are something totally under individual control and must be exercised. High salt and calorie intakes are the leading causes behind various chronic disorders. Simple lifestyle changes and conscious eating habits can go a long way in building a healthy body and happy life.
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