Dietary Glutamic Acid, Obesity, and Depressive Symptoms in Patients With Schizophrenia

Abstract

Introduction: Schizophrenia is a lifelong condition associated with several comorbid conditions such as physical illnesses like obesity, as well as co-occurring psychiatric symptoms such as depression. Research regarding susceptibility to some of these comorbidities has primary focused on genetic risks or neurotransmitters and very little work has been done to understand environmental factors such as diet. In particular, understanding the role of dietary glutamic acid consumption on co-morbidities in patients with schizophrenia is important, as evidence suggests that glutamic acid consumption may directly influence glutamatergic neurotransmission; a key neurotransmitter related to schizophrenia, its associated co-morbidities, and depression. Therefore, the aim of this study was to examine the potential relationship between dietary glutamic acid and depressive symptomatology in patients with schizophrenia, stratified by obesity status, due to its relationship with inflammation, antipsychotic use, and depressive symptoms.Methods: Subjects included in this analysis, were part of a parent cross-sectional study in which included three dietary recalls analyzed using protocols outlined as part of the National Health and Nutrition Examination Surveys (NHANES) standardized criteria. Additionally, body mass index (BMI), and Beck Depression Inventory were obtained at this visit. Subjects with a BMI ≥ 30 kg/m2 were included in the obesity group, and the relationship between glutamic acid consumption and BDI scores was analyzed after controlling for age, race, sex, antidepressant and antipsychotic use, and animal and vegetable protein intake which provide natural forms of dietary glutamic acid.Results: A total of 168 participants were included in this study, of which 42.5% were female and 52.9% were White. The mean BMI for the group as a whole was 33.5 ± 8.7 (kg/m2) and the mean BDI was 14.5 ± 10.2 (range 2–50). No differences were found between obesity groups, other than a greater hyperlipidemia, hypertension, and lower waist to hip ratio. Overall, no relationship was found between dietary glutamic acid and BDI scores, However, for non-obese participants, diets higher levels of glutamic acid were associated with greater depression symptomatology (p = 0.021).Conclusion: These preliminary results indicate a possible correlation between dietary glutamic acid a depressive symptoms in non-obese patients with schizophrenia, although further research is needed to specifically examine this relationship.

Development of a Derivatization Reagent with a 2-Nitrophenylsulfonyl Moiety for UHPLC-HRMS/MS and Its Application to Detect Amino Acids Including Taurine

“…Moreover, a bivalve with large edible parts also contains a large amount of Glu. Excessive Glu intake may exacerbate the depressive symptoms of obese schizophrenia [17].…”

Glutamate and depression: Reflecting a deepening knowledge of the gut and brain effects of a ubiquitous molecule

“…While endogenous brain glutamate has been linked to the pathophysiology of psychiatric conditions such as schizophrenia and mood disorders, the possible role of dietary glutamate (Table 1 ) in the development of neuropsychiatric conditions is still being evaluated[ 42 ]. There have been suggestions that the consumption of diets containing high concentrations of monosodium glutamate could increase body levels of glutamic acid, resulting in hyperglutamatergic neurotransmission, which could possibly contribute to the development of depression[ 43 ]. Also, a few studies have reported that factors such as chronic stress that reduce brain levels of glutamate and glutamine causing hypoactive glutamatergic signaling in the mouse prefrontal cortex are also associated with the development of depression[ 44 ], suggesting that regarding brain glutamatergic transmission a delicate balance always needs to be maintained.…”

“…The relationship between dietary monosodium glutamate and depression has been examined by a few studies[ 35 , 43 , 47 ]. The results of a clinical analysis that examined the relationship between the consumption of a diet high in glutamic acid and the development of depressive symptoms in a group of persons with schizophrenia revealed that in non-obese patients the consumption of high dietary glutamic acid was associated with an increase in depressive symptoms, although this was linked to the susceptibility of persons with one psychiatric condition to develop other co-morbidities[ 42 ].…”

Commentary: Dietary Glutamic Acid, Obesity, and Depressive Symptoms in Patients With Schizophrenia

“…The result is that consuming large amounts of glutamate in food, even when it raises plasma glutamate, does not elevate brain glutamate levels. The articles Kumar et al (1) cite to support glutamate administration affecting brain function involve giving direct systemic injections to animals, thus bypassing gastrointestinal metabolism (17)(18)(19)(20)(21)(22). Such injections produce abnormally large increments in plasma glutamate, sufficient to overwhelm the BBB barrier to glutamate [17-fold increments or more are required (23)].…”

“…Kumar et al (1) collected self-reported 24-h recalls of foods and beverages consumed by patients with schizophrenia. From these data, they estimated 24-h intakes of dietary protein and the glutamic acid present in dietary protein.…”