Friday, August 17, 2012

A recipe for disaster. Creating a food supply for our appetite

I authored this article, it first appeared Twitter @Conversation in 2012
For all but the past 10,000 years, hominin species (2 legged primates) on the human evolutionary tract have been hunter-gatherers, and over millions of years of natural selection our senses were developed and refined to help us navigate the local environment.  Of critical importance was the ability to make correct food choices, and the sense of taste informed the hunter gatherer about the suitability of food for consumption. When a potential food was placed in the mouth the 5 taste primaries informed on essential nutrients and toxins: sweet elicited by sugars reflecting carbohydrate; umami elicited by glutamic and other amino acids reflecting protein content; salt elicited by sodium and other ions (Na+) reflecting mineral content; sour elicited by free hydrogen ions (H+) reflecting excessive acidity; and bitter reflecting potential toxins in foods.   In concert with the taste quality is a hedonic response and sweet, salty and umami qualities are appetitive and encourage consumption, whereas excessive sour and bitter are aversive and promote rejection of the food.  Decisions on whether to swallow or spit the food were critical to preservation of life. Appetitive responses to foods that contained fats, salt and sugars ensured these biologically prized yet scarce nutrients were consumed.
So, over millions of years of evolution, the sense of taste guided the hunter gatherer to essential nutrients and away from potential toxins.  Then approximately 10,000 years ago, the Neolithic revolution was underway and included human mastery of agriculture and animal husbandry meaning a secure food supply, thereby ending the need for hunter-gathering.  Civilisations were established around a secure food supply.
Arguably in the past 50 years there has been more change in the food supply than any other 50 year period with the establishment of fast food empires, multinational food companies, hyper-supermarkets, and a food supply heavily based on our appetitive response; in westernised societies we live in a vastly different environment to our hunter-gatherer forebears.  Our appetitive response is now a relic of evolution, and there has not been enough time since the Neolithic revolution for any adjustment to the human genome. 
Food companies, quite rightly, produce foods that appeal to our appetitive desires.  But, driven by appetite we now consume excess quantities of energy, fats, salts and sugars which lead to diseases of civilisation including obesity, hypertension and related pathologies.  One answer is to produce foods that are appetitive and nutritious, yet contain low concentrations of fats, salts and sugars.  While such strategies have the potential for significant health benefits, it will not be easy and the following example with salt (sodium) illustrates.
Sodium, in the form of manufactured sodium chloride (salt), is found in abundance in the modern diet, and excessive sodium consumption is linked to hypertension, cardiovascular disease and other diseases. Predicted health gains with a modest 15% reduction in dietary salt may avert 8.5 million cardiovascular related deaths worldwide over 10 years making salt reduction a priority for food industries and governments alike. In Westernised societies approximately 75% of our dietary salt intake is from manufactured foods, therefore pressure is on food companies to reduce the level of salt added to foods. 
While salt has certain functionality in foods, palatability and consumer acceptance is the most commonly cited constraint to salt reduction by the food industry. Large reductions in salt content of foods often result in declines in palatability and consumer acceptance of those foods.  The bliss point region represents the intensity of saltiness and the concentration of sodium at which the optimal level of liking occurs.  For example, salt added to a food at low concentrations may result in the food not being salty enough to be perceived and therefore too bland to be liked, while a higher concentration will increase liking until an optimal level of liking is reached.  However, further increases in salt concentration will result in the food becoming too salty, and liking will then decrease. The challenge remains, how can salt be removed while maintaining consumer liking and acceptance of a product. (For a review on the effects salt has on flavour please see Liem et al 2011).  
The food environment has changed significantly over the past 50 years and this has coincided with increased prevalence of diet related diseases.  Our appetitive response to certain nutrients aided the hunter gather survive by making appropriate food choice, but we now have a secure food supply and our appetite is leading us down a path to disease states rather than survival.  As the food supply has been refined in response to drivers of appetite we have created a food environment that promotes obesity, hypertension, certain cancers.  The challenge is to develop a food supply that meets not only our nutritional needs, but also fulfils our hedonic requirements.
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