Over-eating might be in the brain

The sight of rich, creamy icing glistening atop a moist cake. The smell of coffee. The sound of the crisp crunch of a potato crisp. The melting sensation of warm chocolate on your tongue.

Food is a multi-sensory experience that involves our brains as well as all five senses.

It is also a very personal experience: what appeals to one person may be totally different to what another person finds irresistible.

To find out more, food scientist Dr Mei Peng, at the University of Otago, is investigating whether we each have our own ‘sensory fingerprint’. She wonders if this unique fingerprint might explain why some of us are prone to over-eating.

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Are you a sucker for sweets, regularly seduced by a slice of rich cake, or is it the thought of a hot salty chip that has you salivating?

Do you eat for pleasure and find yourself regularly over-indulging, or do you regard food merely as fuel?

For Mei Peng, these questions all come down to sensory processing and how we perceive our world.

“I’m particularly interested in eating behaviour,” says Mei. “So what makes us eat what we eat, and how much.”

Mei and PhD student Rachel Ginieis are in the early stages of a large study in the Food Sciences Department at the University of Otago, in which they are testing normal weight and over-weight people to get insights into their sensory worlds.

The Marsden-funded project is called Searching for a human sensory ‘fingerprint’ – a personalised index of hedonic eating.

Mei explains that we may “each have a unique sensory ‘fingerprint’ that controls reward-related brain networks and determines individual susceptibility to over-eating.”

In other words, some of us may be primed to over-eat rich food, and in a world awash with calorie-rich offerings this may help explain the growing obesity epidemic.

“In today’s food environment, food has become really palatable and really accessible,” says Mei.

One hypothesis about why people have very different responses to food is that we may vary in how much we rely on different senses.

“Some people might be more visually dominant while other people might be more smell dominant,” says Mei, “So that could be one of the reasons we eat so differently.”

Rachel adds that there are interactions between different senses, so although one sense may be dominant, other senses are still providing input to varying degrees.

Building a sensory food map

To develop individual sensory maps, Rachel and Mei are combining a number of experiments.

Noses are put to the test. Does a faint floral smell become fish-like at stronger concentrations?

The tongue is given a workout. What is the lowest concentration of sugar that someone can still perceive as sweet?  Does a sip of a substance called ‘prop’ taste like water or is it intolerably bitter?

When you are presented with a food buffet while wearing an eye tracker, where do your eyes linger on the table? Do your pupils widen in subconscious appreciation at the sight of your favourite food?

What associations do you make between words and images of high-sugar and low-sugar foods?

And what will neuroimaging from a brain scanner reveal about the workings of your brain when you are asked to simply think about food?

And once all the data is in Mei and Rachel will then combine it, to test if their idea of a sensory fingerprint explains why some of us eat more than others.

The size of the problem

Ministry of Health statistics from August 2018 show that ‘New Zealand has the third highest adult obesity rate in the OECD, and our rates are rising. Almost one in three adult New Zealanders (over 15 years) is obese, and one in ten children.’

Understanding how our relationship with food is affected by all our senses may, in future, help individuals to better control their eating and help the country deal with the rising obesity epidemic.