Fructose could lead to lower brain reward than glucose

24-Jun-2015 - Last updated on 25-Jun-2015 at 11:52 GMT

Consumption of isoglucose, which can have a slightly higher fructose content than ordinary sugar, is likely to increase when quotas are removed in 2017

Fructose may lead to overeating by creating fewer reward signals in the brain, suggests a small pilot study published in PLOS ONE.

Researchers from the University of Basel looked at how fructose and glucose – the sugars that make up sucrose, or ordinary table sugar, in a 1:1 ratio – affect interactions between the digestive tract and the brain. They found that among the 12 healthy male participants, fructose stimulated the brain’s reward system less effectively than glucose, as measured by MRI analysis.

“The study may provide the first key findings about the lack of satiety and rewarding effects triggered by fructose,” said lead authors Dr Bettina Wölnerhanssen and Dr Anne Christin Meyer-Gerspach.

Fructose occurs naturally in fruits and vegetables, while glucose – pure grape sugar – is a primary source of fuel for most organisms, including humans. They affect the body differently, with glucose causing a rapid spike in blood insulin, and fructose having a more limited effect.

However, the researchers behind this latest study claim that the way fructose is used in industrially produced foods and drinks could be harmful to health, with its smaller effect on satiety possibly leading to overeating and obesity. They say this is of particular concern as high fructose corn syrup – known as isoglucose or glucose-fructose syrup in Europe – has become more widely used in soft drinks and processed foods, and more ubiquitous in western diets.

“Fructose consumption from industrially produced foods is increasing worldwide, and this may be accompanied by adverse metabolic consequences,” they wrote.

The high fructose corn syrup used in US soft drinks has slightly higher fructose content than sucrose, with 55% fructose and 42% dextrose, while the HFCS usually found in food products is 42% fructose and 58% glucose.

Currently isoglucose use in Europe is governed by a sugar quota system, which limits production to 5% of the total EU sugar quota – but according to some analysts, it could take up to 30% of the market when sugar quotas are reformed in 2017.

“The global obesity problem supports the urgent need for research that aims to understand the basic mechanisms that regulate food intake, appetite and body weight. However, it is unclear how different behavioural and physiological responses to glucose and fructose are mirrored in the neural system including sensory, cognitive and reward processes,” wrote the study’s authors.

“Therefore, we are exploring the role of ingested nutrients in triggering adaptive processes in the brain by uncovering the temporal relations between gut and brain signals that control eating and feeding behaviour and energy consumption.”

Director of Sugar Nutrition UK, Dr Alison Boyd, said that satiety was a worthwhile area for sugar nutrition research, but questioned the study’s validity due to its small scale.

“Its scientific validity is inherently limited at this stage, and conclusions about the impact of fructose on the human body simply cannot be drawn,” she told FoodNavigator.

“In general, it is extremely important to understand that laboratory conditions, where liquid nutrients are given through feeding tubes, cannot simply be translated into everyday eating where a range of different foods are consumed. The most common source of fructose, after all, is unsurprisingly fruit.”

Source: PLOS ONE

doi:10.1371/journal.pone.0130280

“Dissociable Behavioral, Physiological and Neural Effects of Acute Glucose and Fructose Ingestion: A Pilot Study”

Authors: Wölnerhanssen BK, Meyer-Gerspach AC, Schmidt A, Zimak N, Peterli R, Beglinger C, et al.