A recent study published in ACS Chemical Neuroscience examines the impact of high-fat diets (HFD) on impulsivity and inhibitory control, highlighting how such diets may alter brain functions and contribute to long-term behavioral changes.
Inhibitory control is the brain’s ability to suppress impulsive or compulsive behaviors, a skill critical for managing impulsivity, which is a hallmark of several psychological disorders, including attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), autism, and schizophrenia. Impulsivity itself can be broken down into different categories: impulsive action, impulsive choice (preferring immediate rewards over delayed, larger rewards), and reflection impulsivity (a sensory experience that remains untested).
While inhibitory control typically weakens during adolescence, its decline can be exacerbated by diet, substance use, and other environmental factors. Both high-fat and high-sugar diets have been linked to increased impulsive behaviors, potentially through mechanisms involving neuroinflammation, immune system activation, and changes to dopamine (DA) activity in certain brain circuits.
Prior studies have suggested that HFDs increase impulsivity by affecting the mesolimbic and frontostriatal pathways, which regulate behavior and reward. Dopamine receptors (DR1 and DR2) and cannabinoid receptors (CB1) are involved in regulating appetite and play a role in how HFDs affect the brain. Studies on adolescent rats, for instance, have shown mixed results, although certain areas like the nucleus accumbens appear to encourage increased fat intake. Consumption of an HFD over time can alter CB1 activity in the prefrontal cortex, a change that weakens as the diet continues. Furthermore, Brain-Derived Neurotrophic Factor (BDNF) levels rise initially with HFD consumption, though sex-based differences emerge with prolonged exposure.
The study aimed to understand how adolescent exposure to an HFD influences inhibitory control later in life. Researchers used Wistar laboratory rats, exposing them to either an HFD or a normal diet from postnatal day (PND) 33 to PND 77. At the end of the study period, various behavioral tasks were used to assess impulsivity, including the variable delay to signal task (VDS), the five-choice serial reaction time task (5-CSRTT), delay discounting task (DDT), and rodent gambling task (rGT). Afterward, the rats’ frontal cortex was examined for gene expression and sequencing, and their stool samples were analyzed for metabolomics and fatty acid composition.
The study revealed an increase in premature responses among rats exposed to the HFD, suggesting heightened motor impulsivity. These rats exhibited an inclination to make hasty decisions, even when faced with delays, compared to the control group. However, cognitive impulsivity—defined as the tendency to make impulsive decisions despite long-term consequences—was less affected by the diet.
Despite higher motor impulsivity, rats on the HFD were less inclined to take risks, showing fewer impulsive choices. These findings suggest that different types of impulsivity may be influenced by diet in different ways, with HFD consumption particularly affecting motor impulsivity over cognitive impulsivity.
Interestingly, the study found no significant changes in compulsive behaviors in HFD rats, a finding that aligns with previous research. However, there were observations of increased perseverative responses (repeated behaviors despite adverse outcomes) in cases where rats were allowed free access to fatty foods, pointing to the need for further investigation.
Changes in the expression of genes related to food regulation and dopamine systems were noted, especially in male rats. For instance, DRD1 (a gene associated with dopamine regulation) and endocannabinoid system genes exhibited long-term changes, indicating an altered response to food rewards and the DA system. Additionally, BDNF expression increased in males but decreased in females, which correlated with deficits in inhibitory control. This suggests that adolescent females may be more vulnerable to impulsivity as a result of HFD consumption.
The study also found that HFD consumption affected gut metabolism, with increased fatty acid levels and decreased glucose and glycerol concentrations. However, no significant changes were found in omega-3 fatty acids, which have been shown to reduce ADHD-like behaviors and impulsivity in earlier studies.
This study demonstrates that a high-fat diet consumed during adolescence can lead to long-lasting deficits in inhibitory control, particularly in terms of motor impulsivity. However, cognitive impulsivity remained relatively unchanged. The findings point to a complex relationship between diet, brain function, and impulsivity, involving alterations in neuroplasticity, dopamine regulation, and gut metabolism. Future studies are essential to uncover the precise mechanisms by which HFDs influence impulsivity and related brain changes.
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