Unlocking the Gut-Brain Connection: How Diet and Microbes Could Hold the Key to Preventing Parkinson’s Disease

Every nine minutes, someone in the United States is diagnosed with Parkinson’s disease (PD) [1]. Despite tremendous progress in the field, the exact mechanisms behind its pathological initiation and progression is still unclear– how do alpha-synuclein proteins begin building up within dopamine-producing neurons in the brain? New research suggests that researchers may have been previously looking in the wrong place.

Enter the gut-brain axis (GBA). The GBA is a highly integrated network of nerves connecting the central and enteric nervous system. Recent research proposes a potential relationship between our gut bacteria and the neurons influencing neurodevelopment and neuroregeneration– the GBA serves as the link between these two systems [2]. 

Three chief hypotheses could explain this fascinating pathway [1]. First, intestinal microbiota are known to not only break down complex food components that the body can't process, but also develop and regulate the immune system [3]. Motile immune cells in the gut are designed to migrate where needed in the body– including moving towards the brain. Second, researchers predict that the vagus nerve, a key connector of the brain to various organs and digestive tract, could be the conduit for the microbiome connection to the brain. Finally, the microbiome-gut-brain connection could be complemented by chemical communication through  metabolites, or small molecules made by the microbiome to break down food, drugs, and other substances [1].

Many researchers have noted that symptoms in the gut are often the first ones to manifest in PD patients. Dysregulation of the brain-gut-microbiota axis in PD may be associated with gastrointestinal symptoms that precede motor symptoms, supporting the hypothesis that gut could be the source of pathological PD progression [4]. Also, researchers have found alpha-synuclein aggregation in the guts of many PD patients– this led them to sequence the microbiomes of individuals with PD over the years, discovering that beneficial bacteria like Prevotella, Faecalibacterium, and Roseburia are reduced in those with the disease compared to people without it [3].

This connection hints that gut bacteria could help detect neurodegenerative and neurodevelopmental diseases early on. It also suggests that changing the gut microbiome might offer a new way to treat diseases that have been difficult to manage. 

So what’s the answer to potentially preventing PD? While researchers are still determining exactly how the gut and brain are linked in Parkinson's disease, the gut-brain axis is proving to be a critical piece of the puzzle. One of the most exciting aspects of this research is the role diet plays in shaping the gut microbiome. By increasing fiber-rich foods, such as fruits, vegetables, and whole grains, we can support beneficial bacteria that may protect against disease [5]. As scientists continue to explore how gut bacteria influence brain health, dietary interventions could become a key part of preventing or slowing the progression of Parkinson’s. Though research is still in the early stages of delineating this complex relationship, it offers a promising new direction for treatment and prevention strategies that could one day change the lives of millions.

Graphic by Haynes Lewis

Reviewed by Laila Khan-Farooqi

References

[1] Backman, I. (n.d.). Does Parkinson’s Disease Begin in the Gut? Retrieved October 10, 2024, from https://medicine.yale.edu/news-article/does-parkinsons-disease-begin-in-the-gut/ 

[2] Ambrosini, Y. M., Borcherding, D., Kanthasamy, A., Kim, H. J., Willette, A. A., Jergens, A., Allenspach, K., & Mochel, J. P. (2019). The Gut-Brain Axis in Neurodegenerative Diseases and Relevance of the Canine Model: A Review. Frontiers in Aging Neuroscience, 11, 130. https://doi.org/10.3389/fnagi.2019.00130

[3] Klann, E. M., Dissanayake, U., Gurrala, A., Farrer, M., Shukla, A. W., Ramirez-Zamora, A., Mai, V., & Vedam-Mai, V. (2022). The Gut–Brain Axis and Its Relation to Parkinson’s Disease: A Review. Frontiers in Aging Neuroscience, 13. https://doi.org/10.3389/fnagi.2021.782082

[4] Mulak, A., & Bonaz, B. (2015). Brain-gut-microbiota axis in Parkinson’s disease. World Journal of Gastroenterology : WJG, 21(37), 10609–10620. https://doi.org/10.3748/wjg.v21.i37.10609

[5] Bicknell, B., Liebert, A., Borody, T., Herkes, G., McLachlan, C., & Kiat, H. (2023). Neurodegenerative and Neurodevelopmental Diseases and the Gut-Brain Axis: The Potential of Therapeutic Targeting of the Microbiome. International Journal of Molecular Sciences, 24(11), 9577. https://doi.org/10.3390/ijms24119577

The Changing Plate: How Globalization is Changing South Asian Diets and Health

In the world of global cuisine, South Asian tradition has garnered acclaim for its vibrant flavors, diverse ingredients, and health-promoting properties. However, in recent decades, the diets of South Asian immigrants in Western countries have undergone a dramatic transformation, driven by globalization and westernization. This shift has not only altered culinary traditions but has also led to significant health impacts, particularly concerning the rise of chronic diseases such as type 2 diabetes and cardiovascular disease [1, 6, 7].

The Traditional South Asian Diet

Historically, South Asian diets were characterized by whole grains, legumes, vegetables, fruits, and spices, with limited meat composition. This dietary pattern, developed over centuries, was culturally significant and nutritionally balanced. It provides a diverse range of essential nutrients, including fiber, vitamins, and minerals, while relatively low in saturated fats and refined carbohydrates [2, 4, 7, 9]. 

Park and Agarwala (2023) note in their study on cultural shifts and cardiovascular risk traditional South Asian diets were heart-healthy, emphasizing plant-based foods and reasonable portions. The use of spices like turmeric, ginger, and garlic not only enhanced flavor but also provided anti-inflammatory and antioxidant benefits. The traditional diet relied on nutrient-rich whole grains such as millet, brown rice, and whole wheat. The shift toward white rice, processed bread, and sugary snacks spikes blood sugar levels, which leads to insulin resistance and an increased risk of diabetes [1].

The Globalization Effect

As South Asians migrate to Western countries, their dietary habits have rapidly changed. The balanced diet of their ancestors has changed to increased processed foods, fast foods, and sugary beverages, often high in saturated fats, trans fats, sodium, and added sugars. Incorporation of ingredients such as heavy cream, deep-fried foods, and foods that are higher in saturated fats (such as paneer) have become increasingly prevalent. This shift is paired with the overconsumption of the excess carbohydrates already ingrained in South Asian diets, such as white rice, flatbreads, and deep-fried carbohydrate snacks made from bleached flour, all straying further and farther away from a focus on quality plant-based food [1, 2].

This dietary transition involves several significant changes, including:

1. Consuming more white rice and flour, replacing traditional whole grains.

2. Increased consumption of red meat and dairy products.

3. Greater incorporation of processed and convenience foods from Western wholesale stores and supermarkets.

4. Higher intake of sugary beverages and snacks.

Factors Driving Dietary Change

Several interconnected factors contribute to these dietary shifts among South Asian immigrants [9]:

1. Acculturation: As immigrants adapt to new environments, they often adopt local food habits. Lesser et al. (2014) found that greater acculturation is associated with increased consumption of convenience foods, sugar-sweetened beverages, and higher overall calorie intake [3]. 

2. Economic growth and rising incomes: Higher incomes allow greater access to processed foods and eating out.

3. Urbanization: The increasing availability of fast food and convenience foods in urban areas makes these options more accessible.

4. Cultural perceptions: Western foods are sometimes seen as symbols of modernity or higher status, causing people to indulge in them more often. 

5. Time constraints: Busy lifestyles in Western countries often lead to a reliance on convenience foods and relying on fast food. 

6. Globalization of food markets: The increased availability of non-traditional foods in Western and South Asian countries facilitates dietary changes.

7. Food marketing: Aggressive marketing of processed and fast foods influences consumer choices.

Health Consequences

The health consequences of this nutrition transition are severe and multifaceted. South Asian immigrants are experiencing dramatically increased rates of type 2 diabetes, developing the disease at younger ages and lower body mass indexes compared to other ethnic groups. Garduño-Diaz and Khokhar (2012) highlight that South Asians are at a higher risk of developing type 2 diabetes compared to Europeans, with a prevalence rate of 3-5 times higher [6].

Cardiovascular disease risk has also increased significantly. Park and Agarwala (2023) note that South Asians have a higher prevalence of cardiovascular disease compared to other ethnic groups, which is partly due to dietary changes [1].

The rise in obesity rates among South Asian immigrants is particularly concerning. Hu (2011) points out that the “thrifty gene hypothesis” may explain why South Asians are particularly susceptible to weight gain and metabolic disorders when exposed to Western diets. This genetic predisposition to store fat efficiently, previously advantageous in times of food scarcity, becomes detrimental in environments with abundant calorie-dense foods [7].

Microbiome Changes

Recent research has also highlighted the impact of dietary changes on the gut microbiome of South Asian immigrants. The shift to a Western diet is associated with changes in gut microbial composition, potentially increasing the risk of inflammatory bowel diseases and other health issues [5, 8]. This emerging field of research suggests that the health impacts of dietary acculturation may be even worse than previously thought and already have irreversible biological impacts. 

Cultural and Social Implications

The nutrition transition in South Asian communities is not just a matter of individual dietary choices; it's deeply intertwined with broader economic, social, and cultural changes. Ray and Srinivas (2012) in their book "Curried Cultures" explore how globalization has reshaped South Asian foodways, both in South Asia and in diaspora communities. Food acts as a lens through which to view broader social and cultural shifts [4].

Food often becomes a way to maintain connections to their cultural heritage. However, the pressures of acculturation and the convenience of Western foods can lead to the fading away of traditional dietary practices. This tension between maintaining cultural identity and adapting to new environments plays out daily in the food choices of South Asian immigrants [9].

The Need for Targeted Interventions

To address these health disparities and preserve valuable aspects of traditional South Asian diets, there is a critical need for targeted interventions:

1. Culturally appropriate dietary guidelines: These should blend healthy traditional and modern eating patterns, recognizing the cultural significance of food in the South Asian lifestyle.

2. Public health campaigns and education programs: Targeted campaigns for South Asian communities can promote healthier eating habits while respecting cultural food traditions. These can also spread awareness of the dire issue of increasing rates of type 2 diabetes and cardiovascular disease. Raising awareness about the risks associated with adopting Western dietary patterns and the benefits of maintaining aspects of traditional diets is crucial.

3. Improving food environments: Efforts to improve the availability and affordability of nutritious traditional foods in immigrant communities can make healthier choices more accessible.

4. Research: Continued research into the specific dietary needs and health risks of South Asian populations can inform more effective interventions. Medical professionals should also be trained with cultural competence and provide culturally aware care to their South Asian patients who are struggling with diet and mentioned chronic diseases. 

Conclusion

The globalization of food systems has profoundly impacted the diets and health of South Asian immigrants and diaspora in Western countries. While it has increased food diversity, it has also driven a shift towards less healthy dietary patterns that have significantly increased the risk of chronic diseases such as type 2 diabetes and cardiovascular diseases. Balancing cultural food traditions with the realities of Western food environments remains a crucial public health challenge for these communities.

As we move forward, we must recognize that many traditional South Asian dietary practices are naturally sustainable and healthy. By rediscovering and promoting these traditional practices while adapting to modern realities, we can work towards a healthier future for South Asian communities worldwide. The challenge lies in preserving the best aspects of traditional diets while navigating the complexities of modern food systems and lifestyles.

Addressing this issue requires a multifaceted approach involving public health initiatives, policy changes, and community engagement. It also calls for a deeper understanding of the cultural significance of food and the complex interplay between diet, identity, and health. By embracing this complexity and working collaboratively, we can hope to create healthier food environments that honor cultural traditions while meeting the nutritional needs of South Asian immigrants in the 21st century.

Reviewed by Leya Edwards-Headen

References 

[1] Park, J. K., & Agarwala, A. (2023). Cultural Shifts and Cardiovascular Risk: The Westernization of South Asian Lifestyle. The American Journal of Cardiology, 200, 247. https://doi.org/10.1016/j.amjcard.2023.06.056    

[2] Pingali, P. (2007). Westernization of Asian diets and the transformation of food systems: Implications for research and policy. Food policy, 32(3), 281-298. https://doi.org/10.1016/j.foodpol.2006.08.001

[3] Lesser, I. A., Gasevic, D., & Lear, S. A. (2014). The association between acculturation and dietary patterns of South Asian immigrants. PloS one, 9(2), e88495. https://doi.org/10.1371/journal.pone.0088495

[4] Ray, K., & Srinivas, T. (Eds.). (2012). Curried Cultures: Globalization, Food, and South Asia (Vol. 34). Univ of California Press. 

[5] D'Aloisio, L. (2024). A journey from India to Canada: the westernization of the gut microbiome is associated with dietary acculturation in Indian migrants (Doctoral dissertation, University of British Columbia). https://dx.doi.org/10.14288/1.0440970 

[6] Garduño‐Diaz, S. D., & Khokhar, S. (2012). Prevalence, risk factors and complications associated with type 2 diabetes in migrant South Asians. Diabetes/metabolism research and reviews, 28(1), 6-24. https://doi.org/10.1002/dmrr.1219 

[7] Hu, F. B. (2011). Globalization of diabetes: the role of diet, lifestyle, and genes. Diabetes care, 34(6), 1249-1257. https://doi.org/10.2337/dc11-0442 

[8] D'Aloisio, L. D., Shetty, V., Ballal, M., & Gibson, D. L. (2022). Following the Indian Immigrant: adoption of westernization results in a western gut microbiome and an increased risk of inflammatory bowel diseases. FEMS Microbiology Ecology, 98(12), fiac133. https://doi.org/10.1093/femsec/fiac133

[9] Gadgil, M. D., Kandula, N. R., & Kanaya, A. M. (2020). Acculturation is associated with dietary patterns in South Asians in America. Journal of immigrant and minority health, 22(6), 1135-1140. https://doi.org/10.1007/s10903-020-01016-3 

Gut Feelings: Tweaking the Microbiome for Mental Health Treatment

Who would’ve thought part of your digestive system could impact your brain? Since that discovery was made, it’s been a trend in recent years to study the connection between the gut and the brain, called the gut-brain axis. As connections between the brain and mental function are continuously being made, there is the potential to employ the gut-brain axis in mental health therapies. But like with any emerging field in medicine, it raises several ethical considerations that need to be worked through.

The human gastrointestinal tract is inhabited by trillions of microorganisms that are collectively known as the gut microbiome. These microorganisms have been found to play a significant role in human function, specifically in brain activity and mental health, through several mechanisms including neurotransmitter production, immune system regulation, and direct communication within the vagus nerve (1). Given this discovery, we can look at mental health disorders through the gut health lens. Conditions like depression and anxiety are being considered from the perspective of the microbiome (2). As a result, there are new approaches to treating these disorders and reducing the burden on the individuals living with them.

One of the more accessible ways of influencing the microbiome is with probiotics, beneficial bacteria that are usually found in fermented products. Researchers have even coined the term “psychobiotics” to represent the probiotics that induce mental health benefits, such as the Bimuno-galacto-oligosaccharides (B-GOS) and Bacteroides fragilis. Psychobiotics work in three ways: psychological effects on emotional processes, systemic effects on glucocorticoid stress response, and effects on neurotransmitters and proteins (3). An initial comprehensive meta-analysis found that probiotic supplementation had a significant reduction in depressive symptoms (4). Another study even found that a specific combination of probiotics reduced anxiety and improved cognitive ability in patients with Alzheimer’s disease (5).

Ethical questions arise when considering whether patients fully understand that probiotics are experimental treatments, not cures. It’s also important to examine if probiotics should then be considered as pharmaceuticals if they’re part of treating medical conditions, addressing the need to regulate how companies advertise their probiotic products so they don’t overstate their benefits.

A much more extreme treatment option is fecal microbiota transplantation (FMT), a procedure consisting of transferring healthy fecal matter from a donor into a recipient to restore a healthy balance to their microbiome. A case study study showed an improvement in treatment-resistant depression in one patient after FMT, an interesting result for potential future studies. Specifically, there was an increase in Firmicutes and Lachnospiraceae counts and a decrease in Bacteroidetes counts, showing how the microbiome was rebuilt in this patient (6). When using FMT, though, one of the main ethical concerns is the screening process for the donor. Because it is part of the microbiome that is being transferred, the vast-reaching effects of the gut-brain axis play a role in determining a donor because there could be unwanted effects that arise from the donor’s biology. The microbiome is also being drastically changed for the recipient through an invasive process, which puts forth the question of how bad a mental health condition must be before FMT becomes an option. Would the recipient still have the same personality and autonomy after such an immense change?

As with any new avenue of scientific exploration, the ethics of using the microbiome need to be considered at every step. But, this field holds promise, and research should continue to be performed in order to find new avenues for treating mental health disorders. 

Graphic by Ariha Mehta

Reviewed by Sanjana Anand

References 

1. Cryan, J. F., O'Riordan, K. J., Cowan, C. S. M., Sandhu, K. V., Bastiaanssen, T. F. S., Boehme, M., ... & Dinan, T. G. (2019). The microbiota-gut-brain axis. Physiological Reviews, 99(4), 1877-2013.

2. Valles-Colomer, M., Falony, G., Darzi, Y., Tigchelaar, E. F., Wang, J., Tito, R. Y., ... & Raes, J. (2019). The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, 4(4), 623-632.

3. Sarkar, A., Lehto, S. M., Harty, S., Dinan, T. G., Cryan, J. F., & Burnet, P. W. (2016). Psychobiotics and the manipulation of bacteria–gut–brain signals. Trends in Neurosciences, 39(11), 763-781.

4. Ng, Q. X., Peters, C., Ho, C. Y. X., Lim, D. Y., & Yeo, W. S. (2018). A meta-analysis of the use of probiotics to alleviate depressive symptoms. Journal of Affective Disorders, 228, 13-19.

5. Akbari, E., Asemi, Z., Daneshvar Kakhaki, R., Bahmani, F., Kouchaki, E., Tamtaji, O. R., ... & Salami, M. (2016). Effect of probiotic supplementation on cognitive function and metabolic status in Alzheimer's disease: a randomized, double-blind and controlled trial. Frontiers in Aging Neuroscience, 8, 256.

6. Cai, T., Shi, X., Yuan, L. Z., Tang, D., & Wang, F. (2019). Fecal microbiota transplantation in an elderly patient with mental depression. International Psychogeriatrics, 31(10), 1525-1526.