Sugary drinks will be subject to a government levy in the UK. Credit: Anthony Devlin / PA Wire/PA Images. All rights reserved.

Last week, UK Prime Minister Theresa May unveiled a watered-down obesity strategy that left health experts reeling and denouncing it as the first failure of her premiership.

More accurately, the strategy, which committed to a tax on sugary drinks, was unveiled on the PM’s behalf, whilst Mrs May was on holiday, something which critics say reflects a lack of commitment.

The debate over the perils of sugar has simmered away for decades.

Action on Sugar, an expert-led charity which seeks to reduce UK free sugar intake to under 5% of total energy intake, believes a sugar tax is a necessary tool to combat obesity and poor health.

A celebrity endorsement in the form of Jamie Oliver has promoted the campaign for a levy on fizzy drinks, whilst the Scientific Advisory Committee on Nutrition (SACN) reported that the NHS could save £500m a year if the daily maximum intake of sugar was halved and sugary drinks consumption was minimised.

In contrast, People Against Sugar Tax argues that sugar is already taxed in the form of VAT, and represents the patronising action of a nanny state.

Despite the debate on government action, there is a consensus that excess sugar consumption is a cause of obesity, and obesity heightens the risk of developing many serious diseases including diabetes, cardiovascular disease, various cancers, and premature death.

READ MORE: Jamie Oliver’s 'Sugar Tax' – the icing on the austerity cake    

Treating obesity and its consequences alone currently costs the NHS £5.1bn every year, according to a Public Health England report on sugar reduction.

Yet, in the face of these unnerving facts, obesity has become the norm in the western world. According to government statistics, the majority of adults in England are now either overweight or obese, whilst one in three 10-11 year olds and one in five 4 to 5-year-old children are obese or overweight.

If we focus a little higher than the waistline, and consider the effect of sugar on the brain, would this change public attitudes towards obesity and alter behaviour?

How sugar affects the brain

The brain needs sugar (in the form of glucose) to survive and is a metabolically greedy organ. Even at rest, the brain consumes around 20% of the body’s total energy supply, despite only accounting for about 2% of body weight.

The hypothalamus is the brain's major metabolic control center and is sensitive to how much glucose is in the bloodstream. It works in tandem with the pea-sized pituitary gland at the base of the brain to control hormone release and maintain stable blood glucose levels.

The brain runs a slick operation, regulating glucose metabolism with exquisite control; an imbalance can cause neurological chaos. Large changes in blood glucose concentration (hyper- or hypo- glycaemia), which can occur in diabetics, can cause depression, confusion, unconsciousness and in extreme rare cases, brain death.

Alas, no brain is safe from the nasty effects of excess sugar.

The brain of a dementia patient. Credit: Peter Byrne / PA Archive/ PA Images. All rights reserved.  

Excess sugar can harm memory function

High sugar intake can cause memory problems by disturbing the hippocampus, the brain’s memory hub, even in otherwise healthy young people, research has shown.  

And it’s not just adult brains at risk.

Children’s mental abilities are also impaired by refined carbohydrates, which includes all sugars and starches, except those in natural whole foods such as fruit. For example, in a study of 6-7 year-old schoolchildren in Tehran, those who ate a high amount of refined carbohydrates scored worse on non-verbal tests of intelligence.

Even short-term high sugar consumption can be harmful.

Scientists at the University of California fed a group of rats water spiked with fructose for six weeks, equivalent to around one litre of soft drinks a day in humans.  A separate group of rats were given non-spiked water.

After six weeks, the animals who had consumed fructose took twice as long to navigate a maze compared to the non-spiked rats. This suggests that the fructose caused memory impairments, the scientists concluded in the study published in the Journal of Physiology. The scientists also found that hundreds of genes in the hypothalamus (the metabolic control hub), and the hippocampus (the memory hub) were altered in the fructose-fed rats.

"Our findings illustrate that what you eat affects how you think,” said the lead scientist from UCLA's Brain Research Institute.

Excess sugar and brain diseases

The risk of developing Alzheimer’s disease is increased by a high-sugar dietDementia is a public health priority, with the World Health Organisation (WHO) suggesting that the number of people living with dementia will triple by 2050.

Although scientists can’t predict who will and won’t develop dementia later in life, obese middle-aged people have twice the average risk of developing dementia in older age, recent studies show.

The risk of developing Alzheimer’s disease is increased by a high-sugar diet and is also increased two-fold with diabetes. In the face of a dementia epidemic, scientists are urgently trying to work out what it is about sugar that puts the brain at risk in the hope that they can intervene.

Excess sugar also seems to affect the brains ability to heal after injury.

Consuming high amounts of artificial sugar not only puts you at an increased risk of having a stroke (when poor blood flow to the brain causes cell death), it also affects post-stroke recovery. People with higher blood glucose levels tend to recover less well, and have a higher rate of post-stroke infections. Similarly, patients with pre-existing high blood-sugar levels and diabetes have poorer outcomes after a head injury.

Although this paints a picture sufficiently dismal to make you resist that mid-afternoon sugar fix, what many of these studies lack is a clear cause and effect. High sugar consumption could instead be a surrogate for other poor health behaviours, and may be a cover for the true brain assassin.

To get closer to cause and effect, greater experimental control is needed, and hence, animal studies. Highly-controlled animal studies indeed corroborate the evidence from patients; rats fed a high-fructose diet recovered less well from a head trauma, scientists at UCLA in California have shown.

“Our findings suggest that fructose disrupts plasticity — the creation of fresh pathways between brain cells that occurs when we learn or experience something new”, Fernando Gomez-Pinilla, a professor of neurosurgery and integrative biology and physiology at UCLA said.

Evidence suggests obesity is harmful to the brain. Credit: Clara Molden / PA Archive/ PA Images. All rights reserved.

An obese brain is a damaged brain?

Excess sugar may inflict a multi-pronged insult to the brain. Long-term excess sugar consumption commonly results in obesity, which is associated with worse memory and thinking skills, according to research evidence.

For example, a study of middle-aged people showed that a higher body mass index (BMI) was associated with poorer performance when asked to remember a list of numbers. Whereas we all get cognitively slower as we grow older, a higher BMI speeds up cognitive ageing.

This is especially worrying given the concomitant increasing ageing population and increasing prevalence of obesity in the UK today.

READ MORE: Is our ageing population the problem we think it is?

To understand what is causing these impairments, scientists have used brain imaging techniques to compare the brains of obese people to those who are a healthy weight.

Brain regions communicate with each other via neural ‘white matter’ highways. Both the functioning, and the communication pathways of the hippocampus memory hub may be disturbed by obesity, evidence suggests.

White matter pathways in the human brain, visualised using diffusion magnetic resonance imaging(MRI). Credit: Flickr / Alfred Anwander, MPI-CBS. Wellcome Images. Some rights reserved (CC BY-NC-ND 2.0)

Dr Claudia Metzler-Baddeley, a neuroscientist at Cardiff University Brain Research Imaging Centre, looked at these white matter neural pathways and how their structure related to BMI. She found that the structure of the fornix, a C-shaped bundle of neural fibers which carry messages from the hippocampus, was related to BMI.

The emerging picture of poor brain health related to excess sugar consumption is worthy of alarm. Clearly an effective national and worldwide strategy to target the obesity epidemic and the throng of harmful effects on health is desperately needed.

Less obvious is whether the government’s sugar tax will be sufficient to achieve this. Sugar is only one slice of the proverbial pie, with an emerging field dedicated to the harmful effects of sedentary lifestyles on the brain.

The opportunity to fund health programmes for schoolchildren – many of which have been eradicated by austerity cuts –  through the collected sugar tax should be welcomed as a step forward in a very long path ahead.