Recent research published in the Journal of Affective Disorders sheds light on how consumption of ultra-processed foods (UPFs) is associated with increased depressive symptoms and reduced brain volume in brain areas associated with processing rewards. These relationships were discovered to be influenced by obesity and inflammation levels.
As its name suggests, UPFs are foods that have been altered significantly. These foods contain fewer nutrients, protein and dietary fiber, but have an increased energy density due to being high in fatty acids, sugars, and salt. UPFs also often contain additives to increase palatability, bolstering industrial sales and profits.
Recent studies have demonstrated that UPF consumption is associated with an increased risk of developing depression. Yet the mechanisms explaining how this occurs in the brain are unclear, with some research suggesting that inflammation within the frontolimbic network of the brain plays a role. The frontolimbic network involves the frontal lobe areas (involved in decision-making and planning) and the limbic system (involved with emotions and memory).
The study team, led by Oren Contreras-Rodriguez from Josep Trueta University Hospital in Spain, set out to unpack the relationship between UPF consumption and depressive symptoms.
The researchers firstly aimed to provide new insights by investigating how this UPF consumption-depression association is related to brain volumes in humans. Additionally, the team investigated the potential impact of obesity upon this association, as obesity has been found to be associated with higher consumption of UPFs. Finally, the study authors sought to investigate if biological signs of inflammation (inflammatory biomarkers) play a role in this UPF consumption-depression relationship.
Contreras-Rodriguez and colleagues recruited 152 adults who were roughly 50 years old on average. 63 were not obese, and 89 were obese.
These participants completed questionnaires on diet and depressive symptoms, and underwent magnetic resonance imaging (MRI) assessments to capture brain volume data. Laboratory tests were also administered, which measured inflammatory biomarkers such as the amount of white blood cells in the body.
The study team discovered a positive association between UPF consumption and depression. In other words, high UPF consumption was significantly linked with a higher presence of depressive symptoms.
Furthermore, UPF consumption was negatively linked with brain volume. Specifically, high UPF consumption correlated with lower volumes in the left amygdala and the posterior cingulate cortex of the brain.
The amygdala and the posterior cingulate cortex are involved in the brain’s reward system, playing a pivotal role in food choices, “[the] posterior cingulate cortex … receives information about actions being performed and whether the actions were rewarded through the information sent from the amygdala. In this way, the posterior cingulate cortex helps to adapt behavior to obtain rewards and avoid punishers.”
In other words, the amygdala and the posterior cingulate cortex process information about past experiences with food, influencing future decisions based on whether a particular food was considered rewarding or not, and UPF consumption may be modifying these processes.
When exploring only participants with obesity, higher UPF consumption was similarly associated with depressive symptoms, in addition to lower volumes in the amygdala and the posterior cingulate cortex.
However, additional areas involved in the mesocorticolimbic network were revealed to have reduced volume, one of which was the left ventral putamen. “Together with the amygdala, the ventral putamen has been associated with food-triggered motivation. The ventral putamen … is implicated in reward processing and habitual behavior, and plays a key role in the control of food intake, with its altered connectivity being associated with food craving in individuals with excess weight.”
Simply put, this brain region is important in driving the “wanting” of foods, and changing the connectivity of this region is associated with food cravings in obese individuals.
The dorsomedial frontal cortex was another brain region discovered to be of reduced volume.
“The dorsomedial frontal cortex participates in … cognitive control processes … it has been associated with the ability to resist the urge for an immediate reward (e.g., palatable foods such as UPF) versus maintaining the effort to achieve long-term goals (e.g., positive health).”
To simplify, this brain area is important in decision-making. In particular, this region controls the ability to resist immediate rewards such as tasty foods in favor of long-term goals like maintaining a healthy lifestyle, and UPF consumption could potentially be altering this.
Finally, UPF consumption was significantly positively associated with white blood cell levels – indicating greater inflammation. Additionally, the association between UPF consumption and depression was influenced by white blood cell levels. However, inflammation biomarkers did not influence the association between consumption of UPFs and brain volume.
Despite these significant findings, the study precludes any causal conclusions, as only correlational associations were revealed. For example, the study cannot definitively claim if eating UPFs directly contributes to depressive symptoms and brain volume changes. Another limitation is that the researchers employed food frequency questionnaires which relied on participant memory over a long period, and biases may have unintentionally influenced the data.
The study, “Consumption of ultra-processed foods is associated with depression, mesocorticolimbic volume, and inflammation”, was authored by Oren Contreras-Rodriguez, Marta Reales-Moreno, Sílvia Fernández-Barrès, Anna Cimpean, María Arnoriaga-Rodríguez, Josep Puig, Carles Biarnés, Anna Motger-Albertí, Marta Cano, and José Manuel Fernández-Real.