Why food is nothing without texture

Consider the classic summer treat, an ice cream cone: what actually happens in our brain when we take a bite?

First, clusters of brain cells in the somatosensory system come into action. These brain cells are associated with our sense of touch, temperature and pain. The mouthful of ice cream warms to body temperature, coating the tongue and inside of the mouth, releasing the creamy fat texture.

At the same time the orbitofrontal cortex of our brain chimes in with a rating of just how delicious that scoop of goodness is. The two regions begin to communicate, with the link becoming stronger still when the ice cream is high in fat and, fortunately, in your favourite flavour.

For true ice cream fans an even greater reward response is triggered. A further section of the brain, the cingulate cortex thought to be linked to actions and emotional responses, identifies ice cream as responsible for the state of your happiness and signals a system-wide thumbs up. With all that brain chemistry fizzing, we are urged to repeat the experience, again and again, until little of that wonderful ice cream is left.

The takeaway is that taste, commonly defined as salt, sour, bitter, sweet and umami, is not solely responsible for driving those positive brain vibes. The texture of what we eat is also important.

Individual differences in preferences and cravings affect this response of the brain. If you like ice cream, the combination of a desirable taste, with an equally desirable fat texture, creates an even more rewarding brain response.

My research looks at how our brains respond to the texture of our foods. Food texture is an important factor in whether we like or dislike food. Just imagine eating a pavlova without the crunchy exterior that holds a gooey sweet centre? Few of us would accept a pavlova that lacked the right set of textures, unless out of politeness to the host.

We know too that eating an apple and drinking its equivalent in juice are two different experiences. The texture and the chewing an apple requires makes us feel full, a glass of the same apple juiced does not.

There remain many questions about the role texture plays in our brain’s response to food. Part of the problem is that studying the brain when people are eating is tricky. Researchers want to see which parts of the brain light up when eating a favoured texture. MRI (Magnetic Resonance Imaging) scans reveal what’s happening in our brain.

The problem is the need to remain as still as possible during a scan. To figure out what’s happening we need to take brain scans when people are eating and therefore, moving. This is painstaking work because the act of chewing requires our head to shift about. If the person moves too much the MRI scan will be blurry and little will be revealed.

We tackle this problem by letting participants have one small bite and then we ask them to lay as still as possible while we scan their brains. We use custom-made lollies with different textures to help us analyse which brain areas identify food textures. Our research is one of the first studies to use solid food rather than liquids.

So why is it important to understand how our brain responds to food? The bigger story here is that New Zealanders are facing an obesity epidemic. One in three New Zealanders above the age of 15 are now obese, and these numbers are ever increasing.

Part of the problem is that we live in an obesogenic environment. At no point in human history have foods dense in calories, sugars and fats been so available and affordable to so many people. However, our brains have not caught up with these changes in food availability and their wiring is still attuned to high-value energy-dense foods.

The fight against obesity is a battle on multiple fronts. Over-consumption of fats and sugars lie at the heart of this issue. To unravel and understand the addictive nature of fat and sugar, we need to understand how our brain responds to their consumption. We know that different parts of the brain light up to taste and smell, as well as the sight of fatty and sugary foods that we like. What we lack knowledge about is how our brain identifies and appreciates the texture of these highly addictive foods.

By researching which brain regions are involved in experiencing food texture, we can build a map of how pleasurable textures, especially fat texture, in combination with a delicious taste, triggers connections between brain regions and increases our reward responses.

With a map, we can investigate the potential mechanisms for why fats, in general, are so hard to resist and perhaps even finally answer the question of why we find ice cream so delicious.