A sweetener used in fizzy drinks, biscuits, cakes and ice cream could be fuelling ADHD in kids, according to new research.
Fructose lowers energy in cells, triggering a ‘foraging’ response similar to starvation which leads to risk taking and aggression.
Eating too much has been linked to cardiovascular disease, cancer, diabetes and dementia. It has been dubbed “the world’s deadliest sugar”.
Now scientists have found it sparks manic behaviour – and the reason can be traced back to human evolution.
Lead author Professor Richard Johnson, of the University of Colorado, said: “We present evidence fructose, by lowering energy in cells, triggers a foraging response similar to what occurs in starvation.”
It stimulates risk taking, impulsivity, novelty seeking, rapid decision making and aggressiveness to aid the securing of food for survival.
Over-activation of this process from excess sugar intake causes conditions ranging from ADHD to bipolar disorder – and even aggression, he explained.
Added Prof Johnson: “While the fructose pathway was meant to aid survival, fructose intake has skyrocketed during the last century and may be in overdrive due to the high amounts of sugar that are in the current Western diet.”
Fructose is found in fruit, where its effects are naturally counteracted. But when it is refined and added to sweeten products it is worse for you than glucose.
Prof Johnson said: “We do not blame aggressive behaviour on sugar, but rather note it may be one contributor.”
The World Health Organisation claims eating a small amount a day is fine. But most people in the UK consume too much – leading to the introduction of the ‘sugar tax’ in April 2018.
Experts say the sugary foods we should cut down on are sweets, cakes, biscuits, chocolate and fizzy drinks, many of which contain fructose.
Prof Johnson said: “Behavioural Disorders are common and are associated with obesity and the western diet.
“Excessive intake of fructose in the form of high fructose corn syrup and refined sugars may largely contribute to these conditions.”
He added: “The identification of fructose as a risk factor does not negate the importance of genetic, familial, physical, emotional and environmental factors that shape mental health.”
The cause of psychiatric disorders remain a mystery despite decades of research – and the key may lie in anthropology, he said.
For animals in the wild, the source of fructose was limited to that in honey and fruit, or to fructose generated in the body.
But the introduction of refined sugar and high fructose corn syrup has increased consumption 40-fold since the 1700s.
Prof Johnson said: “As such, western societies are eating much more fructose than nature intended. Indeed, overactivation of this ‘survival pathway” has had a major role in driving the epidemics of obesity and diabetes.
“One of the consequences of the fructose-based survival pathway is that it stimulates the foraging response.
“The foraging response shares similarities with certain behavioural disorders including ADHD, bipolar disorder or even aggressive behaviour.
“One study, for example, reported subjects who scored higher on ADHD traits tended to also show more exploratory behaviour, consistent with the idea ADHD may reflect a type of foraging response.
“Here we present the hypothesis the high intake of sugar may be a major stimulus of this foraging response that may assist in driving externalising behavioural disorders associated with impulsivity, attention deficit, hyperactivity and mania.”
Previous research found rats given fructose water for two months put on more weight than those given water spiked with glucose.
They also had higher levels of harmful fats in their bloodstream and unhealthy arteries.
Cooked starchy products with a ‘high glycaemic index’ such as white rice, pasta and potatoes, as well as salty foods, may also contribute as they can be converted to fructose in the body.
Prof Johnson said: “Some studies suggest uric acid produced during fructose metabolism may mediate some of these effects.”
He added: “Chronic stimulation of the pathway could lead to desensitisation of hedonic responses and induce depression.
“In conclusion, a hyperactive foraging response driven by high glycaemic carbohydrates and sugars may contribute to affective disorders.”
The study is published in Evolution and Human Behavior.