OBESE NATION: It’s time to admit it – Australia is becoming an obese nation. This series looks at how this has happened and, more importantly, what we can do to stop the obesity epidemic.
Today we look at how we got here, with Russell Keast explaining how, by creating food to suit our appetite, we have found the recipe for nutritional disaster, while Garry Egger looks at economic growth and why we should use the economic slowdown to try to shrink our waistlines.
For all but the past 10,000 years, the hominin species (two-legged primates) on the human evolutionary tract have been hunter-gatherers. And over millions of years of natural selection, our senses developed and were refined to help us navigate the local environment.
Of critical importance to our survival was the ability to make correct food choices and our sense of taste informed the hunter-gatherer about the suitability of food for consumption.
When a potential food was placed in the mouth, the five-taste primaries informed the brain about 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.
Working in concert with these tastes is a hedonic response with sweet, salty and umami qualities being appositive (working together) and encouraging consumption. Meanwhile excessive sour and bitter tastes are aversive and promote the rejection of the food.
Decisions on whether to swallow or spit the food are critical to preservation of life. Appetitive responses to foods that contained fats, salt and sugars ensured these biologically prized yet scarce nutrients were consumed. Over millions of years of evolution, the sense of taste guided the hunter-gatherer to essential nutrients and away from potential toxins.
The downside of civilisation
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 and the end of the need for hunter-gathering. Civilisations were established around a secure food supply.
Arguably, there’s been more change in the food supply in the past 50 years 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 hasn’t been enough time since the Neolithic revolution for any adjustment to the human genome.
Food companies produce foods that appeal to our appetitive desires. But, driven by appetite, we now consume excess quantities of energy, fats, salts and sugars, leading 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, as the following example with salt (sodium) illustrates.
What’s a grain of salt?
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. It’s predicted that a modest 15% reduction in dietary salt may avert 8.5 million cardiovascular-related deaths worldwide over ten 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, so the pressure is on food companies to reduce the level of salt added to foods. Salt has certain functionality in foods – palatability and consumer acceptance are the most commonly cited constraints to salt reduction by the food industry and large reductions in salt content of foods often result in declines in palatability and consumer acceptance of those foods.
This can be seen in the Bliss Point graph below:
The bliss point region represents the intensity of saltiness and the concentration of sodium at which the optimal level of liking occurs.
Salt added to food at low concentrations may result in the food not being salty enough to be perceived and too bland to be liked, while a higher concentration will increase liking until an optimal level is reached. But further increases in concentration will result in the food becoming too salty, and liking will then decrease.
So the challenge of how can salt be removed while maintaining consumer liking and acceptance of a product remains.
The significant change in the food environment over the past 50 years has coincided with increased prevalence of diet-related diseases. The appetitive response to certain nutrients aided the hunter-gather survive by making appropriate food choices, 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 and certain cancers. The challenge is to develop a food supply that meets not only our nutritional needs, but also fulfils our hedonic requirements.
This is part four of our series Obese Nation. To read the other instalments, follow the links below:
Part three: Explainer: how does excess weight cause disease?
Part twelve: Putting health at the heart of sustainability policy
Part thirteen: Want to stop the obesity epidemic? Let’s get moving
Part fourteen: Fat of the land: how urban design can help curb obesity