Is a Western diet a risk factor for major depressive disorder?

By Shanet Susan AlexAug 8 2023Reviewed by Sophia Coveney

In an article published in the Nutrients journal, researchers investigated whether the Western diet (WD) was a risk element for major depressive disorder (MDD) patients.

Background

The most common cause of disability around the world now is depression, affecting around 300 million people. Depression is a psychiatric illness connected to inflammation.

The sickness behavior theory explains the connection between depression and inflammation. The more receptive areas of the blood-brain barrier (BBB), such as the choroid plexus and the circumventricular organs, may allow immune cells and cytokines to enter the central nervous system (SNC) during an inflammatory or infectious condition.

Additionally, a neural circuit is implicated in inflammation through the afferent fibers of the nerves. These signals cause psychological and somatic manifestations of inflammation, such as depressive mood and fever.

The WD, a high sugar and fat diet, is linked to inflammation. The numerous links between inflammation and WD have been examined thoroughly. WD contains excess nutrients like trans fatty acids (TFAs) and saturated fatty acids (SFAs). Further, it is deficient in protective nutrients like monounsaturated fatty acids (MUFAs), n-3 polyunsaturated fatty acids (n-3 PUFAs), antioxidants (AOs), minerals, and dietary fibers (DFs). 

However, whether MDD patients follow a WD and it operates as a risk factor for MDD is unknown.

About the study

In the present study, the investigators assessed whether WD could be a risk factor for MDD by conducting a transversal analysis of those with MDD and controls with no comorbidities. They carried out blood evaluations, such as C-reactive protein (CRP), an advanced glycation end-product (AGE) analysis, and a diet anamnesis.

The primary goal of the research was to demonstrate that MDD patients with no comorbidities harbored higher CRP levels than controls. The second objective was to determine whether their diet would be a risk factor by examining the ratio of anti-inflammatory (anti-inflammatory, gut-microbiome intervention (AGMI), DFs, AOs, and n-3 PUFA) and pro-inflammatory (TFAs, sugars, n-6 PUFA, and SFAs) nutrients as well as the AGE level and glycemic load. 

The overall pro-inflammatory component of the diet in MDD patients was determined. The team sought to demonstrate that the diet of MDD patients offered higher nutritional risk elements than those of the controls, assuming the control population had a WD.

Finally, the researchers conducted correlation analyses between the nutritional risk variables and the CRP levels in the multi- and univariate analyses to support the relationship between inflammation and nutrition in this setting.

Results

The team found that 34.37% of MDD patients demonstrated a CRP level over 3-10 mg/L that remained greater than controls following adjustments for body mass index (BMI), sex, smoking status, and age. The MDD patients had an excess of TFAs, SFAs, and sugar compared to controls.

They were deficient in monounsaturated fatty acids (MUFAs), n-3 PUFA, AOs, and DFs. Similarly, the MDD patients exhibited aggravating nutritional elements and a high glycemic load relative to the controls. 

In addition, the MDD patients had lower dietary consumption of protective micronutrients and their sources than controls for fruits and vegetables (F&V) and vitamin C. Depending on sex, this was also true for zinc, vitamins E and A, and magnesium.

CRP and nutritional factors were correlated in multivariate and univariate analysis models. A positive association was found for the CRP status of the MDD patients and TFAs, fat, short-chain fatty acids (SCFAs), n-6 PUFA, and free sugars (FSs), and a negative association for CRP status and F&V intake in the univariate model.

FSs, fat, TFAs, and SCFAs positively correlated with the CRP status in multivariate analysis contrary to F&V.

Hence, MDD patients displayed a raised CRP status and a WD trend that might have a role in maintaining an inflammatory state. 

Conclusions

According to the study findings, MDD patients with no comorbid conditions had higher CRP levels than controls, and this was particularly relevant for low-grade inflammation.

The diets of MDD patients displayed greater degrees of nutritional risk elements than the controls and harbored a general pro-inflammatory profile. The researchers discovered that a persistent high-glycemic-load diet, along with nutrient excesses and deficits, some of which were associated with sex, may be responsible for this dangerous profile. 

The correlation between the nutritional risk variables and the CRP level highlighted the WD-linked risk of maintaining an inflammatory environment. A newly emerging or pre-existing imbalanced diet may be made worse by MDD. This vicious cycle may prolong inflammation and oxidative stress alongside comorbid conditions like obesity and diabetes. 

In a nutshell, the present study emphasizes the significance of the general characteristics of WD and its management during MDD. Nonetheless, more research is needed to verify these findings.