Mental Health Awareness Week: Professor Robert Thomas explains how sugar damages mental wellbeing 

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While it’s common knowledge that sugar is bad for the body, Professor Robert Thomas explains why it’s bad for your mental health too

Robust clinical studies have firmly established that overindulgence of refined sugar is one of the most harmful dietary habits we can inflict on our bodies. It increases the risks of premature ageing, diabetes and early death from the biggest killers of mankind including cancer, heart disease, and stroke.

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What's less emphasised in the popular literature is its negative impact on brain and mental health although the scientific evidence is just as overwhelming. Here's why:

Fatigue, low mood and demotivation

Sugar has a high glycaemic index meaning it is rapidly absorbed into the body raising blood levels dramatically that gives us a short term high. In response, insulin levels rise rapidly causing sugar levels to fall drastically.

This yo-yoing, high and low sugar, causes low energy levels which, coupled with poor gut health (see below), leads to fatigue and demotivation to embark on other healthy lifestyle habits such as exercise. Contrary to popular opinion a scientific review of 31 studies found that eating a tub of ice cream or a box of chocolates does not improve mood, it actually lowers mood and happiness scales.

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What's more, an analysis of data from a large study involving British civil servants reported that men with a high consumption of sugary drinks and ultra-processed foods had a 58% increased risk of depression.

In our hospital, we replaced sugary snacks with nuts and fruits at nursing and doctor stations and staff rooms. By four months, the study showed that average weight of the staff decreased but more importantly measures of happiness improved.

Overwhelming scientific evidence proves refined sugar can have a negative effect on mental health. Picture: PAOverwhelming scientific evidence proves refined sugar can have a negative effect on mental health. Picture: PA
Overwhelming scientific evidence proves refined sugar can have a negative effect on mental health. Picture: PA | Press Association Images/Press Association Images

Insomnia

Studies have shown that sugary foods in the evening, can disrupt regular sleep patterns by adversely affecting the sleep hormones melatonin and cortisol. Sleep is important for mental health as it recharges the energy stores in every cell, and clears up toxic metabolites which have built up over the day. It slows the brain cell cycles allowing more time for repair of our precious DNA. Insomniacs have an increased risk of depression, anxiety and suicide and in the long term dementia.

Weight gain and obesity

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The appealing nature of high calorific sugary food combined with their low satiating nature means they tend to be eaten in excess which contributes to obesity. Furthermore, the post spike dip, leaves people ravenous, further encouraging overeating. Obesity, in some people, is associated with a risk of social isolation, agoraphobia, anxiety and depression.

Poor gut health (Dysbiosis)

Several studies have found that sugar preferentially feeds the bad bacteria in our guts whereas good bacterial feed off other forms of energy such phytochemicals. Unfortunately, despite not having the same calorific content, artificial sweeteners were found to do the same thing. Both can lead to dysbiosis, gut inflammation leading to food intolerances, bloating and wind.

A chronic inflamed gut contributes to a "leaky gut syndrome" which causes toxins to leak into the blood stream triggering an inappropriately inflammatory reaction throughout the body. This elicits collateral damage to many organs including the joints causing arthritis and brain fatigue, leading to reduced ability to concentrate, poor cognition and depression. Over time this leads to build up of inflammatory proteins such as amyloid causing dementia.

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Dysbiosis is also linked to more severe consequences of covid and other virus increasing the risk of post viral syndrome which is associated with brain fog, anxiety and depression. Gut dysbiosis also effects hormone imbalance which can increase menopausal symptoms such as hot flushes and low mood. This is why strategies to reduce the negative effects of menopause should include reducing sugar and enhancing gut health.

How can we reduce the impact of sugar

Identify and avoid sugar such as glucose, fructose or sucrose (table sugar) added to food tea, coffee, fizzy drinks, sweets, mints and toffees. Try to wean yourself off adding sugar to tea or coffee and particularly avoid adding sugar to savoury foods during cooking.

Sometimes, it’s not so obvious where sugar has been added, so it's a good idea to get into the habit of reading the label of crisps, other snacks, salad dressings, pasta sources, yoghurt, muesli cereals or those branded as ‘diet’ which often contain high levels of sugar or sugar substitutes.

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Whole fruits are tasty, very healthy and have relatively low sugar levels compared to processed sugar. They are rich in fibre, minerals, vitamins and phytochemicals which, as well as anti-inflammatory and antioxidant effects slow the transport of sugar across the gut wall.

The same cannot be said for juices or smoothies as the fibrous structure is broken down, and sugar hits the bloodstream much faster. Many of the fruit juices on the market aren’t even ‘real’ fruit juices. They consist of mixed concentrates with extra sugar liberally added.

Ramp up the phytochemicals which as well as slowing the glycaemic index they have multiple other benefits for brain health. Aside from fruit, phytochemicals are present in colourful plant based foods such as vegetables, teas, nuts, seeds and spices.

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Switch to slow release carbohydrates which have a lower glycaemic index such as whole meal sourdough bread instead of white bread, whole meal pasta instead of white varieties and using wild rice instead of white rice.

Change your breakfast habits to avoid processed sugar on an empty stomach. This is particularly harmful as it is absorbed even more rapidly. Try to avoid sugary cereals, jam, bread with added sugar or even dried fruit which increases the sugar content from around 10% to 80%. Alternatively go for nuts, whole fruit or a cooked breakfast with eggs, tomatoes, mushrooms and spinach.

Consider intermittent fasting. As well as lowering processed sugar intake intermittent fasting has been investigated as a means, not only to control weight but protect the brain. One review of the scientific studies reported that the 5:2 diet was linked to better mood and a lower rate of depression.

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In conclusion, sugar is one of several dietary and lifestyle habits, that although not always easy, is something we have control of which has been shown, to significantly impact brain and mental wellbeing.

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