Exploring the Impact of Unhealthy Diets on Brain Chemistry and Structure

A May 2024 study highlights the profound impact that diet quality can have on mental health and brain structure. The study “Adherence to unhealthy diets is associated with altered frontal gamma-aminobutyric acid and glutamate concentrations and grey matter volume: preliminary findings” delves into this complex relationship, focusing on how diet influences neurochemistry and brain morphology.

The study looked at 30 adults divided into two groups: those who ate a healthy Mediterranean diet and those who didn’t. They used special brain scans to check the levels of certain brain chemicals (glutamate and GABA) in the medial prefrontal cortex, and to measure the size of certain brain areas (grey matter volume).

The medial prefrontal cortex (mPFC) is located at the front of the brain, just behind the forehead. It is part of the prefrontal cortex, which is involved in complex cognitive behaviour, decision-making, and moderating social behaviour. The mPFC specifically plays a role in functions such as emotional regulation.

Below is a summary of the key findings:

1. Diet Quality and Neurotransmitter Balance:
   • The study found that individuals with lower diet quality had reduced concentrations of GABA and elevated levels of glutamate in the mPFC. GABA is an inhibitory neurotransmitter, while glutamate is excitatory, and their balance is crucial for normal brain function.
   • An imbalance, particularly reduced GABA and increased glutamate, is often observed in anxiety and depression.
2. Impact on Grey Matter Volume:
   • Participants with lower diet quality also exhibited reduced grey matter volume in the right precentral gyrus (rPCG). Grey matter is essential for processing information in the brain and executing actions.
   • The reduction in grey matter volume is concerning as it suggests that poor diet quality could lead to structural brain changes that might affect cognitive and emotional functions.
3. Rumination and Brain Structure:
   • The study noted a significant negative correlation between rumination (repetitive, negative thinking) and rPCG-grey matter volume. This implies that individuals who ruminate more tend to have lower grey matter volume in this brain region.
   • Additionally, there was a marginally significant association between rumination and elevated mPFC-grey matter volume concentrations, further linking diet, brain chemistry, and mental health.

What does this tell us?

These findings suggest that poor dietary habits can negatively affect brain chemistry and structure, potentially leading to or exacerbating mental health issues. The observed changes in neurotransmitter levels and grey matter volume highlight just how important diet is in maintaining brain health.

• Excitatory/Inhibitory Balance: The balance between GABA and glutamate is crucial for preventing excitotoxicity, which can lead to neuronal damage. Diets rich in unhealthy fats and low in beneficial nutrients may disrupt this balance.
• Grey Matter Volume: Reduced grey matter volume can impair cognitive functions and is associated with various psychiatric conditions. The study’s results indicate that diet quality could be a modifiable factor influencing brain structure.

Mood-Food Interactions

Although this study was admittedly small, it further emphasizes the need for dietary interventions as part of integrative mental health treatment strategies. Nutritional psychiatry, which focuses on the impact of diet on mental health, plays a crucial role in this approach. We should be promoting high-quality diets rich in nutrients like polyphenols, fibre, antioxidants, and monounsaturated fats. This type of approach could help support better mental health outcomes and protect against the structural brain changes as well as imbalances in GABA/Glutamate, as seen in this study.