We know high fat and high sugar “junk” foods are bad for our health, but we often sneak them into our diets. Sometimes it just feels like our brain wants us to eat a bar of chocolate or scoff down a whole pizza.
Neuroscientists like me have been studying the effects of these foods on the brain, which helps us to understand how diets can affect brain function.
This is Part 6 and the final of our series on the gut-brain axis, diet and brain health.
Your brain loves junk foods
Your brains are hardwired to make you want to engage in the behaviours you find pleasurable – like having sex, socialising and eating tasty foods – all vital for the survival of a species. When you eat tasty junk foods your brain’s reward system (the mesolimbic dopamine system) activates and releases the neurotransmitter dopamine.
But the brain adapts when we eat lots of rewarding foods and responds by making more receptors for dopamine. The simplest way to think of the interaction between dopamine (or any neurotransmitter) and its receptor is to think of a lock and key where the receptor is the lock and the neurotransmitter is the key. Turning the key sparks a neural impulse.
When we make more dopamine receptors, we need to eat more of the reward (junk foods) to get the same ‘goooooood’ feeling, similar to how addicts can develop a tolerance to drugs. The brain wants us to eat tasty foods and then it wants more, and more!
Junk foods grab our attention and make us impulsive
Our attention is drawn towards what feels good, and in a world full of junk foods it can be difficult to resist sweet temptations.
The brain’s decision-making centre – the prefrontal cortex – controls our behaviour. Eating excess junk foods can impair prefrontal cortex function. This can lead to impulsive behaviours and poor decision making – like eating a whole box of cookies instead of cooking a healthy meal.
Fighting these temptations is difficult when faced with the strategic placement of sweet treats by supermarket checkouts, chocolate muffins in your local coffee shop, or bold adverts for fast food. All of these prompts trigger us to want these foods and can be hard to resist.
Junk foods can impair your memory
The high levels of refined sugars and saturated fats in junk foods leads to a state of inflammation in the brain that damages brain cells (neurons). Rats that gorged themselves on a diet of sugary drinks, cakes and cookies for just five days had signs of inflammation in the hippocampus and struggled with memory tasks.
The hippocampus is the brain’s memory centre and is vital for remembering new information. Neurons in the hippocampus form connections that are constantly being reorganised, a process we call neuroplasticity. This enables us to learn and form memories in response to the constant influx of information in our dynamic world. Junk food filled diets also reduces key brain chemicals required for neuroplasticity, impairing memory.
Research also shows that people who eat lots of junk food also perform badly in memory tests compared to those who eat healthily, irrespective of body weight (i.e. you don’t have to be overweight for these foods to impact your brain’s health).
But it’s not all bad news…
Understanding how junk foods can impact your brain, it one simple steps to modify your lifestyles to reduce their negative effects. It is important to be aware of what is in the foods we eat, particularly when pre-packaged foods are marketed as ‘healthy’.
Exercising and eating healthily are vital for keeping both our body and brains in good shape. I hope you read my previous blog about foods that can boost your brain’s performance…
Image: Eye-catching sweet treats can be hard to resist… http://www.Flickr.com CC BY-NC 2.0
About Dr Sarah
I’m an Oxford University-educated neuroscientist, presenter of ABC Catalyst, director of The Neuroscience Academy, and author of The Women's Brain Book. The neuroscience of health, hormones and happiness.
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