Eating low-calorie sweetened products – especially when hungry or tired – may lead to a higher likelihood of seeking high-calorie alternatives later, due to a newly discovered signal in the brain, according to new research from the Yale University School of Medicine.

The results of the study, published on 23 September 2013 in The Journal of Physiology, implied that it is difficult to food the brain by ingesting ‘energyless’ sweet flavours. The researchers found that the pleasure in consuming sweet solutions is driven to a great extent by the amount of energy provided. That is, greater reward in the brain is attributed to sugars compared to artificial sweeteners.

“The consumption of high-calorie beverages is a major contributor to weight gain and obesity, even after the introduction of artificial sweeteners to the market,” said Professor Ivan de Araujo, lead author of the study from the Yale University School of Medicine. “We believe that the discovery is important because it shows how physiological states may impact on our choices between sugars and sweeteners,” he said.

Specifically, the researchers said their study implied that people frequently ingesting low-calorie sweet products in a state of hunger or exhaustion may be more likely to ‘relapse’ and choose high calorie alternatives in the future.

“The results suggest that a ‘happy medium’ could be a solution,” Professor de Araujo said. “Combining sweeteners with minimal amounts of sugar so that energy metabolism doesn’t drop while caloric intake is kept to a miniumum” he said.

Brain signal picks sugar

The study identified a specific physiological brain signal that is critical for determining choice between sugars and sweeteners. This signal regulates dopamine levels – a chemical necessary for reward signaling in the brain – and only arises when sugar is broken down into a form where it is usable as fuel for cells of the body to function.

The research was performed in mice using a combination of behavioural testing involving sweeteners and sugars, while measuring chemical responses in the brain circuits for reward. The researchers believe the findings are likely to be similar in humans.

“According to the data, when we apply substances that interfere with a critical step of the ‘sugar-to-energy pathway’, the interest of the animals in consuming artificial sweetener decreases significantly, along with important reductions in brain dopamine levels,” Professor de Araujo said.

“This verified by the fact that when hungry mice – who thus have low sugar levels – are given a choice between artificial sweeteners and sugars, they are more likely to completely switch their preferences towards sugars even if the artificial sweetener is much sweeter than the sugar solution,” Professor de Araujo said.

The researchers said that now they knew dopamine cells were critical in the sugar or sweetener choice, they hoped to identify the associated receptors and pathways in the brain.

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