Australasian Science: Australia's authority on science since 1938

Obesity Is Winning the Hunger Games

By Guy Nolch

Can a sugar tax save us if obesity has already permanently suppressed the satiety signals that tell us to stop eating?

When I was at school I was incredulous at a health promotion campaign that urged people to find 30 minutes per day to exercise. I was a skinny, hyperactive kid who barely had time to eat. I knew that adults had to work longer than schoolkids, but how could they not find the time – or desire – to chase a ball for half an hour each day?

Fast forward to the present and we see many people using wearable devices to count how many steps they take each day, as well as monitor other health parameters such as heart rate and quality of sleep. We’re better educated about the food we should eat, and have a wider range of healthier options available. And there’s no end of fitness equipment and diet programs to order from the many “lifestyle” channels available 24/7.

Yet obesity rates have continued to rise, with the Victorian Health Department estimating that about 80% of Australians will be overweight or obese within 9 years. This is alarming not only because being overweight or obese is associated with cardiovascular disease and diabetes, but also because obesity alters our metabolism permanently.

In this edition of Australasian Science, Dr Amanda Page of The University of Adelaide’s Centre for Nutrition and Gastrointestinal Disease explains that the responses of vagal afferent nerves in the gastrointestinal tract are significantly dampened in obese individuals (http://www.australasianscience.com.au/article/issue-may-2016/stomach-tar...), particularly where a high-fat diet has induced obesity. In these cases the vagal nerves become less sensitive to stretching of the stomach, so the brain doesn’t receive the signal that it’s time to put down the cutlery and step away from the table.

Page warns that dieting won’t correct this loss of our gastronomic self-control: the dampened response to satiety continues even after an individual has lost weight and is no longer obese. This would explain why dieters lose weight only to put it back on again.

More encouragingly, Page’s group has identified a target for a pharmacological agent. While these nerve channels are activated in pain-sensing nerves and are responsible for the heat we experience when we eat hot chillies, they also play a role in satiety signalling.

Satiety is just one aspect of the battle of the bulge. As former hunter-gatherers we have a primal urge to consume energy-rich sources of energy, so we shouldn’t be surprised that Tim Tams are so addictive. Indeed, Australian scientists have now discovered that drugs used to treat nicotine addiction can also stop sugar cravings (see Browse, p.7).

Sugar has become the current dietary villain, and the UK is introducing a sugar tax to reduce consumption. Should Australia introduce one too? While Australian researchers have found that a 20% rise in the cost of sugary drinks would save 1600 lives and prevent thousands of heart attacks and strokes each year (http://tinyurl.com/hy4xr48), Prof Tim Olds has reviewed the literature and found that sugar consumption has been falling for 15 years and the evidence against it is unconvincing (see The Fit, http://www.australasianscience.com.au/article/issue-may-2016/pure-white-...).

We need to take matters into our own hands. If we can’t overcome the addictive nature of sugar or restore our lost perception of when our bellies are full, we could do worse than return to the advice given to Norm, the cartoon couch potato from my childhood: find 30 minutes to exercise, or follow the Fitbit fad and take 10,000 steps each day.

Guy Nolch is Editor/Publisher of Australasian Science.