Sugar and the brain

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Our brain is our best friend. A friend we often take for granted! 

To keep the brain healthy, we need to eat healthily. That means more whole foods, less ultra-processed foods, and limiting consumption of added and free sugars.

Why? Read on. 

Activating reward centre
When eating sugary foods, the brain’s reward system is activated. The brain adapts, enjoying the pleasurable hits, further reinforcing the behaviour to reach for more sweet foods. The more we eat, the more tolerant we become, so we are required to consume more to feel sated.

In addition, evidence suggests that neurotransmitters produced by a network of neurons in the part of the brain involved in impulse control and delaying gratification (i.e. responsible for curbing the cravings) are affected by a high-sugar diet, adding to a vicious cycle of desire and reduced ability to stop reaching for high sugar foods. 

Whether added sugars can be formally classified as “addictive” is still to be determined. 

Anecdotally, many individuals have experienced difficulty reducing intake following a diet high in added and free sugars. Research into withdrawal symptoms experienced by humans is mostly translated from animal studies but thought to have a similar biological impact on humans.  

There is evidence the intense desire for added sugars, added fats, and the ultra-processed foods they come in could be considered a “substance use disorder”, where typical behaviours include cravings, compulsive overeating, and eating in the absence of hunger. (Keep in mind, ultra-processed products are designed to make us eat more.) A 2018 paper in Frontiers in Psychiatry demonstrated “sugar addiction” meets five of the eleven criteria for substance use disorder, according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). 

The neural circuits involved in addictive-like behaviours – particularly toward sweet foods that offer an easy energy source – have evolved as a means for survival. But in our modern-day, with easy access to cheap, hyper-palatable, ultra-processed food, these functions are no longer helpful.

Importantly, the more added sugar (and the ultra-processed foods they often come in) consumed, the greater the potential impact on everyday and long-term brain function.

Sugar, the brain and everyday health concerns

Sugar and inflammation
Inflammation is a normal and healthy bodily process activated when injured or infected. Once healed, the inflammatory response is dialled down. However, certain dietary and lifestyle factors can keep the inflammatory response activated long-term. Low-grade, chronic inflammation is implicated in a wide range of conditions, including neurodegenerative diseases. 

Along with factors such as smoking, medication and chronic stress, diet is a major contributor to chronic inflammation. This includes high and persistent sugar intake, impacting the brain, immune system, and other systems in the body. Inflammation has also been implicated in depression.

Sugar and cognition
Ever experience brain fog? You aren’t alone. The energy slump following a sugar-high can leave anyone struggling to think clearly, critically analyse or even talk properly! 

When there is glucose in the blood, the body produces insulin to help shepherd the glucose into cells for their use. When blood glucose is high, the insulin produced results in a dramatic drop in glucose levels, leaving one very low in energy. 

In the throes of an energy slump, it is incredibly difficult to focus and learn. The body compensates for the lack of energy by producing stress hormones, which can result in symptoms such as shakiness and altered thinking and behaviour.

The brain is the most energy-hungry organ in the body, and without a slow and sustained release of energy that one gets from consuming whole foods, we quickly run out of resources required to concentrate. 

Studies show dietary patterns typically high in added sugar and ultra-processed foods, such as the Western-style diet, can adversely impact the part of the brain critical to learning, memory and mental health. Moreover, eating more sugary foods leaves less room for foods that nourish the brain. 

Sugar and mood
When feeling low, stressed or overwhelmed, it is common to reach for cake, chocolate or a cookie. Consuming something sweet can boost your mood, right? 

Recent research has found that one feels worse after that immediate sugary hit than before, experiencing fatigue and an energy slump. 

Authors of a 2019 review suggest high added sugar consumption leads to changes in neurobiological brain function, altering emotional states and subsequent behaviours.

High consumption of added or free sugar and ultra-processed foods can negatively impact mental health by increasing the risk for low mood and worsening anxiety symptoms or feelings of overwhelm.

This may be due to the blood sugar rollercoaster we subject ourselves to after drinking a soft drink, eating a bag of Skittles or a bowl of sweetened breakfast cereal.

If you are experiencing persistent low mood, anxiety or overwhelm, we encourage you to chat with your trusted healthcare practitioner, who can refer you to a registered psychologist. You can also connect with any of the amazing support services out there, such as Lifeline and Beyond Blue in Australia.

Sugar, the brain and long-term health concerns
A negative impact on the brain can manifest later in life. As shown in animal models, diets high in added sugar can result in changes to the hippocampus, a memory centre of the brain. 

High blood glucose, insulin resistance, and chronic inflammation – each a common outcome of a high-sugar, Western-style diet – can impact brain function and make a person more susceptible to cognitive decline.

Insulin resistance has been associated with an increased risk for cognitive decline. A longitudinal study in 2018 observed a linear correlation between high blood glucose levels and potential for cognitive decline, irrespective of whether the individual has diabetes. 

This has been suggested in previous research, including this prospective study which found that higher glucose levels were associated with an increased risk of dementia in populations without and with diabetes. More recently, a study found the earlier the onset of Type 2 diabetes, the greater the risk for dementia.  

What you can do

In good news, there is plenty you can do with diet and lifestyle to love your brain to the next level.

Dietary factors
Research is ongoing to gain a clearer understanding of the relationship between diet, brain function, and mental health. 

Generally, consuming real, whole foods can be beneficial for the brain and overall health, and it is the eating pattern as a whole that matters most.

For example, a systematic review found the “MIND Diet” – a way of eating comprising whole foods such as leafy greens, berries and sources of healthy fats – could improve cognition in older adults; and results from the SMILEs randomised control trial found participants with depression who improved their diet the most and adapted to an eating pattern similar to a Mediterranean-style diet experienced the greatest benefit to their depression.

In these eating patterns, added and free sugars, foods with a high glycaemic load, and ultra-processed ingredients and products are limited. Such foods, typical of the Western-style diet, lack beneficial nutrients, are easy to over-consume and can elicit an inflammatory response.

If you are after some specifics, here are some of the dietary factors to consider:

• Balance blood sugar by eating small amounts often. Ensure meals comprise mostly whole foods, providing sources of fibre, healthy fats, and good quality protein.
• Boost berry intake. Berries are full of flavonoids beneficial to the brain – the richer the colour, the better.
• Include foods rich in omega-3 fatty acids 2-3 times per week, such as oily fish, walnuts, chia and flaxseed. These are brain-protective, and low intake is associated with depression.
• Eat a variety of veg in an array of colours. Aim for at least 5 serves a day, including cruciferous vegetables and 1-2 serves of dark leafy greens. Vegetables are packed with phytonutrients, antioxidants, minerals and vitamins that are integral to brain health.
• Enjoy eggs (especially the yolks) which contain choline and other vitamins needed for brain function and regulating mood.
• Get a serving of fermented foods daily. These can be beneficial for gut health, which in turn can help protect the brain from inflammation.
• Feast on healthy fats. These can include cold-pressed extra virgin olive oil, avocado, nuts, seeds, olives, and oily fish.
• Hydrate with at least 2 litres of water a day. A guzzle of nature’s elixir can often clear a murky mind.

Lifestyle factors
In addition to diet, there are multiple lifestyle factors potentially implicated in brain function and mental health. 

These can include – but are not limited to – getting good quality sleep and regular exercise, less screen time and more time in nature, enjoying creative and cognitively stimulating activities, managing heavy metal exposure, social engagement, and managing stress (chronic or acute). Keeping other aspects of your health in check, such as high blood pressure, high cholesterol or diabetes, is also important. 

What are some dietary and lifestyle factors in your control that you can introduce to support brain function and mental health? You can introduce changes gradually, one step at a time. Every little bit helps, and your brain will thank you!

By Angela Johnson (BHSc Nut Med.)