According to a newly published study, eating a poor quality diet can lead to changes in the brain that are associated with depression and anxiety. This research was a first-of-its-kind study carried out by the University of Kings College London, and is published in Nutritional Neuroscience. https://www.tandfonline.com/doi/full/10.1080/1028415X.2024.2355603 in which brain chemistry and structure was evaluated in relation to diet in 30 study volunteers.
They found that when someone eats a poor quality diet, there is a reduction in GABA (gamma aminobutyric acid) and an elevation of glutamate — (both neurotransmitters), along with reduced grey matter volume in the frontal area of the brain.
Researcher Dr Piril Hepsomali, of the University of Reading, says, “We can eat ourselves well! Ultimately, we see that people who have an unhealthy diet — high in sugar and saturated fat — have imbalanced excitatory and inhibitory neurotransmission, as well as reduced volume of grey matter in the frontal part of the brain. This part of the brain is involved in mental health issues such as depression and anxiety.”
The exact way in which this affects the brain in this way is still being studied. Following the observations of prior animal studies, it appears that obesity and diets that are high in saturated fats cause changes in glutamate and GABA metabolism and neurotransmission. Also, alterations of the gut microbiome due to this dietary pattern is thought to have an impact on the cells that regulate GABA and glutamate production.
These types of unhealthy diets also make the blood glucose higher resulting in higher levels of the hormone insulin, with negative health consequences. This increases glutamate in the brain and plasma, reducing GABA production and release. Having a diet high in fat and cholesterol causes changes in cell membranes that alter the release of neurotransmitters. And these changes in brain chemistry might lead to the changes in the brain grey matter volume observed in the study.
Dr. Hepsomali continues, “I would like to note that GABA and glutamate are intimately involved in appetite and food intake, too. Reduced GABA and/or increased glutamate might also be a driving factor in making unhealthy food choices. So, there may be a circular relationship between eating well, having a healthier brain and better mental wellbeing, and making better food choices to eat well.”
Brain scans show changes in neurotransmitters and grey matter volume in people who have poor diets high in sugar and saturated fat, versus those who eat a Mediterranean style diet, widely considered a healthier dietary pattern. The researchers also found that these changes are also associated with rumination, a part of the diagnostic criteria for conditions affecting mental health, such as depression and anxiety.
Journal Reference – Piril Hepsomali, Adele Costabile, Marieke Schoemaker, Florencia Imakulata, Paul Allen. Adherence to unhealthy diets is associated with altered frontal gamma-aminobutyric acid and glutamate concentrations and grey matter volume: preliminary findings. Nutritional Neuroscience, 2024; 1 DOI: 10.1080/1028415X.2024. 235560 University of Singapore, Yong Loo Lin School of Medicine
Mental disorders such as depressive and anxiety disorders, affect around 300 million people globally. Subclinical symptoms associated with mental disorders such as low mood, worry, and anxiety are even more prevalent.Ruminative negative thinking, defined as uncontrolled, excessive and repetitive thinking about one’s problems, past experiences and worries about the future have been shown to be a factor in common mental disorders. These afflictions are associated with impaired frontal excitatory/inhibitory balance and reduced grey matter volume. Larger grey matter volume is associated with people who adhere to high quality diets. There have also been other studies that have shown altered GABA and glutamate in relation to diet quality. In this study, they examined the associations between diet quality, and frontal cortex neuro-chemistry and structure.
Unhealthy diets affect GABA and GLUTAMATE via their impact on glucose and insulin levels. Western diets rich in saturated fat and cholesterol increases the average glucose and plasma insulin levels, and high glucose increases glutamate release reducing GABA production. These diets change alter cell membranes and damage the organelles and protein structures, and neurotransmitter release. Also, unhealthy intestinal microbiome environments with reduced abundance of good bacteria such as Bacteroidetes may also explain these findings due to GABAergic and glutamatergic receptor activity of the microbiome-gut-brain axis. Due to GABA’s role in regulating food intake and appetite, reduced frontal GABA and/or increased frontal Glutamate concentrations increase neuronal hyperexcitability, resulting in making unhealthy food choices. Evidence from other studies in obesity and overeating supports this idea.
Other recent systematic research reviews have shown a positive correlation with lower diet quality diets and reduced frontal brain volume. These results could reflect a loss of neuronal homeostasis and an increase in neuroinflammation, and subsequently neuronal dysfunction or death in individuals who follow unhealthy diets. It is also felt that high levels of cholesterol may interfere with the supply of oxygen-rich blood supply to the brain (via the accumulation of plaques), leading to neuronal health deficits. And conversely evidence shows that adhering to healthy diets such as the Mediterranean diet high in antioxidants, anti-inflammatory nutrients, and fibre were generally associated with preserved brain structures.
Future research needs to be done with larger numbers of study participants to confirm these findings, and to assess whether higher adherence to healthy diets may restore the E/I balance and reverse the impact of excitability on grey matter volume and on disorders such as anxiety and depression.
Another Large Study About Diet and Mental Health
In a study involving over 13,000 participant residents of Singapore, spanning nearly to 20 years, higher consumption of fruits during midlife was associated with lower odds of depression later in life. The study was published in the Journal of Nutrition, Health and Aging, giving us insight into the potential benefits of eating sufficient fruit in reducing the risk of depressive symptoms later in life.
The researchers studied 14 fruits that are the most commonly consumed in Singapore. They found that the consumption of most fruits – oranges, tangerines, bananas, papayas, watermelons, apple and honey melon, were associated with reduced likelihood of depression. The association could possibly be the high levels of antioxidants and anti-inflammatory micronutrients in fruits — such as vitamin C, carotenoids and flavonoids — which have been shown to reduce oxidative stress and inhibit inflammatory processes in the body that may affect the development of depression.
Principal Investigator of the study Professor Koh Woon Puay of the Signapore School of Medicine said, “Our study underscores the importance of fruit consumption as a preventive measure against ageing-related depression. In our study population, participants who had at least 3 servings of fruits a day, compared to those with less than one serving a day, were able to reduce the likelihood of ageing-related depression significantly by at least 21%. This can be achieved by eating one to two servings of fruits after every meal. We did not see any difference in our results between fruits with high and low glycemic index. Hence, for those with diabetes, they can choose fruits with low glycemic index that will not raise blood sugars as much as those with high index.”
The study participants at an average age of 51 years, answered a detailed questionnaire regarding how often they consumed 14 fruits and 25 vegetables. Over twenty years later those participants at an average age of 73 years, were evaluated for depressive symptoms. This research team found that higher consumption of fruits, was associated with lower odds of depression.
As populations age worldwide there is an increased prevalence of late-life depression among older adults. This is related to underlying neurodegenerative changes in the brain associated with ageing. The needs of this growing group of people has encouraged researchers to evaluate how the risk of late-life depression might be lessened, and the evidence is growing that dietary factors may play a major role in protecting against depression in aging. They are still trying to answer the question- Could a specific diet or food items consumed earlier in life have an impact on mental well-being in later years?
