Summary: After twelve days of daily sugar intake, researchers observed significant changes in both the brain’s dopamine and opioid systems in pigs. Opioid-system changes appeared immediately after the very first exposure to sugar.
Source: Aarhus University
The debate over whether certain foods can be addictive remains contentious. Researchers at Aarhus University investigated how repeated sucrose intake affects brain reward circuitry by studying minipigs that consumed sugar water. Their findings indicate that sucrose alters the brain’s reward systems in ways that resemble the changes caused by addictive drugs. These results were published in the journal Scientific Reports.
Cravings for tasty foods are familiar to many people; the urge to snack on chocolate or sweets can be difficult to resist. The question addressed by this study is whether those strong desires reflect changes in brain chemistry similar to addiction.
“There is no doubt that sugar has several physiological effects, and there are many reasons why it is not healthy. But I have been in doubt of the effects sugar has on our brain and behaviour; I had hoped to be able to kill a myth,” says Michael Winterdahl, Associate Professor at the Department of Clinical Medicine at Aarhus University and one of the study’s main authors.
The research followed seven female Göttingen minipigs that were given two liters of sucrose solution each day for twelve consecutive days. The team used positron emission tomography (PET) to image the animals’ brains before any sucrose exposure, after the first exposure, and again 24 hours after the final (twelfth) exposure. This schedule allowed the researchers to track both immediate and short-term changes in neurotransmitter receptor availability.
After the 12-day exposure period, the study found substantial reductions in the availability of μ-opioid receptors and dopamine D2/3 receptors across multiple brain regions. These declines were observed in the striatum, nucleus accumbens, thalamus, amygdala, cingulate cortex, and prefrontal cortex—areas closely linked to reward processing, motivation, and emotion. In contrast, opioid-system activity increased after a single sucrose exposure, evidence consistent with acute opioid release associated with pleasurable experiences.
When the brain encounters a meaningful stimulus—whether a natural reward like social contact or a learned accomplishment—it can release neurotransmitters that generate feelings of pleasure and reinforcement. Both natural rewards and pharmacological agents can activate the same reward circuitry, involving dopamine and opioid signaling. Winterdahl explains that if an artificial stimulus such as sugar reliably produces a stronger or more immediate reward signal, it can overshadow natural sources of pleasure.
We chase the rush
“If sugar can change the brain’s reward system after only twelve days, as we saw in the case of the pigs, you can imagine that natural stimuli such as learning or social interaction are pushed into the background and replaced by sugar and/or other ‘artificial’ stimuli. We’re all looking for the rush from dopamine, and if something gives us a better or bigger kick, then that’s what we choose,” Winterdahl explains.
Animal models are commonly used to study how specific substances affect reward circuitry. Rodents are frequently employed, but the minipig offers important advantages for translational imaging studies. The pig brain is gyrated like the human brain and is larger than a rodent brain, enabling clearer imaging of deeper structures using human clinical scanners. Furthermore, the controlled laboratory setting allowed the researchers to isolate sucrose intake as the primary variable, avoiding confounding lifestyle factors that complicate human studies, such as diet variability, social experiences, or changes in daily activities.
The PET imaging used two radioligands: [11C]carfentanil to assess μ-opioid receptor availability and [11C]raclopride to assess dopamine D2/3 receptor availability. Voxel-wise binding potentials were calculated using the cerebellum as a reference region. Statistical mapping and regional analyses revealed that after twelve days of sucrose access, both tracers showed significantly lowered binding potential in reward-related regions, suggesting down-regulation or decreased availability of those receptors. After just one sucrose exposure, the opioid tracer showed decreased binding in the nucleus accumbens and cingulate cortex, which is consistent with acute opioid release.
Source:
Aarhus University
Media Contacts:
Professor Michael Winterdahl – Aarhus University
Image Source:
The image is in the public domain.
Original Research (open access):
“Sucrose intake lowers μ-opioid and dopamine D2/3 receptor availability in porcine brain.” Michael Winterdahl, Ove Noer, Dariusz Orlowski, Anna C. Schacht, Steen Jakobsen, Aage K. O. Alstrup, Albert Gjedde & Anne M. Landau. DOI: 10.1038/s41598-019-53430-9.
Abstract (summary)
Excessive sucrose consumption can produce addiction-like craving that may contribute to the obesity epidemic. Opioids and dopamine mediate the rewarding effects of both drugs of abuse and palatable foods. Using PET imaging with [11C]carfentanil and [11C]raclopride in seven anesthetized female minipigs, researchers measured receptor availability before sucrose exposure, after the first exposure, and after 12 daily exposures. After 12 days of sucrose access, binding potential of both tracers declined significantly in reward-related brain regions, consistent with receptor down-regulation. After a single sucrose exposure, reduced [11C]carfentanil binding in nucleus accumbens and cingulate cortex indicated opioid release. The observed reductions in opioid and dopamine receptor availability may help explain the reinforcing, potentially addictive, properties associated with sucrose intake.