A study of adults with borderline personality disorder in the Chicago area found that those who ate more foods high in both saturated fat and added sugar tended to report greater motor impulsiveness, a tendency to act without thinking. Higher saturated fat intake was also linked to more risk-taking on a gambling task, but diet was not associated with the overall severity of borderline personality disorder symptoms. The paper was published in Nutritional Psychiatry.

Borderline personality disorder, or BPD, is a mental health condition characterized by intense emotions, unstable relationships, difficulties with self-image, and impulsive behavior. People with BPD often struggle to regulate their emotions and may engage in risky behaviors, such as excessive spending, substance misuse, or binge eating. Although specialized psychotherapy can help, about half of adults with BPD do not respond to it, highlighting the need for additional approaches.

One potentially important but largely overlooked factor is nutrition. Research has linked diets high in saturated fat and added sugar, which are common in processed foods, to greater impulsivity. Such foods may also influence the brain’s reward system and inflammatory processes, potentially affecting how people experience and manage emotions.

At the same time, people may turn to highly palatable foods in response to stress or negative emotions, suggesting that the relationship between diet and psychological functioning could work in both directions. Research on diet in BPD is limited, but one study found that women with BPD ate fewer omega-3 fatty acids and fewer foods typical of a Mediterranean diet than healthy controls. In two clinical trials, omega-3 supplements combined with the medication valproic acid appeared to reduce some BPD symptoms, particularly anger.

Study authors Sophie Boutouis and Jon E. Grant of the University of Chicago wanted to examine the relationship between saturated fat and added sugar consumption and BPD symptoms, as well as differences in diet across demographic groups. They hypothesized that higher intake of saturated fat and added sugar would be associated with more severe BPD symptoms, more co-occurring psychiatric disorders, poorer decision-making, and greater impulsivity.

The participants were adults from the Chicago area who enrolled in a clinical trial testing the antipsychotic lumateperone as a treatment for BPD. To take part, they had to be between 18 and 65 years old, have a primary diagnosis of BPD, and have symptoms above a set severity threshold; people with schizophrenia, bipolar I disorder, or moderate or severe substance use disorders were excluded. The analysis used data collected at the trial’s first visit, before treatment began.

Of 60 eligible participants, 57 completed the diet questionnaire and were included in the analysis. Their average age was 32, about 72% were women, and about half identified as white.

Participants reported how often they had eaten various foods high in saturated fat and added sugar over the past year using the Dietary Fat and Free Sugar – Short Questionnaire, which produces separate scores for foods high in saturated fat, foods high in added sugar, and foods high in both. They also completed the Barratt Impulsiveness Scale and the Cambridge Gambling Task, a computerized test of decision-making in which risk-taking is measured by how many points participants bet. Clinicians assessed co-occurring psychiatric disorders and suicidal thoughts using the Mini-International Neuropsychiatric Interview and rated the severity of BPD symptoms over the past week.

After accounting for age, race, depression, and suicidal thoughts, participants who ate more saturated fat tended to bet more on the gambling task, indicating greater risk-taking. After accounting for age, those who ate more foods high in both saturated fat and added sugar tended to report greater motor impulsiveness. Added sugar intake on its own was not linked to any of the impulsivity, decision-making, or symptom measures.

Contrary to the main hypothesis, diet was not associated with the overall severity of BPD symptoms, other aspects of impulsivity, or other aspects of decision-making. The authors note that diet was measured over the past year while symptom severity was measured over the past week, which may help explain why no link emerged.

The researchers also found demographic differences. Black participants reported eating more saturated fat than participants from several other groups, and people who ate more foods high in both fat and sugar tended to be older. Participants without depression or recent suicidal thoughts reported eating more saturated fat than those with these conditions, and those with a substance use disorder reported eating less added sugar.

“Saturated fat and added sugar consumption in the past year may be associated with domains related to BPD (i.e., impulsivity, risk-taking behavior). As causality cannot be inferred due to the cross-sectional design of this study, future research should examine whether improvements in nutrition may lead to reductions in BPD symptoms,” the study authors concluded.

The study contributes to the scientific understanding of BPD. However, it should be noted that the study was conducted on a relatively small group of participants seeking treatment in a clinical trial, and results in other groups may differ. The study also did not examine participants’ medication or psychotherapy status, and, as the authors noted, its cross-sectional design does not allow causal inferences.

Because of this, it remains unknown whether high intake of fat and sugar contributes to impulsiveness or whether impulsiveness leads people to eat more of these foods. Other factors not measured in the study, such as body mass index or physical activity, could also play a role. Diet was self-reported over a full year, which can be difficult to recall accurately, and participants may have underreported unhealthy foods.

The paper, “Associations between dietary fat and sugar intake and impulsivity in adults with borderline personality disorder,” was authored by Sophie Boutouis and Jon E. Grant.