Scientists from the University of Chicago studied how diet is linked to symptoms of borderline personality disorder (BPD), a mental condition in which a person has difficulty managing emotions, relationships are unstable, and impulsivity is elevated. The work was published in the journal Nutritional Psychiatry.
The study involved 57 adults aged 18 to 65 with a diagnosis of BPD who were being recruited for a clinical trial of a medication. The mean age was 32, about 72% were women, and roughly half identified as white. Participants completed a questionnaire on how often over the past year they ate foods high in saturated fat and added sugar, underwent tests of impulsivity and decision-making, and had a clinical interview.
After adjustment for age, race, depression and suicidal thoughts, it emerged that the more saturated fat a person consumed, the more points they scored in the computerized gambling game Cambridge Gambling Task, that is, the greater their propensity for risk. And those who ate more foods combining saturated fat and added sugar reported higher motor impulsivity, a tendency to act without thinking. Added sugar on its own was not linked to any of the measures.
Contrary to the authors' expectations, diet was not linked to overall BPD symptom severity, other aspects of impulsivity, or decision-making. The researchers explain this by a possible mismatch of time periods: diet was assessed over a year, while symptoms were assessed over the past week. In addition, demographic differences were found: black participants ate more saturated fat than members of other groups, and people without depression or recent suicidal thoughts consumed more saturated fat than those who had such conditions.
It is important to emphasize: the study was cross-sectional, meaning data on diet and symptoms were collected at a single point in time. Such a design does not allow causal relationships to be established. It is unknown whether fatty and sweet food leads to impulsivity or, conversely, impulsive people more often choose such food. In addition, the sample was small and included only those seeking treatment as part of a clinical trial, and participants self-reported their diet over a full year, which may be inaccurate. Medication use, psychotherapy, body mass index and physical activity were also not taken into account.
The authors conclude: "Consumption of saturated fat and added sugar over the past year may be linked to domains relevant to BPD (impulsivity, risky behavior). Since causality cannot be inferred due to the cross-sectional design, future studies should test whether improving diet can lead to a reduction in BPD symptoms."