Types of Diets vs. Inflammation: a Brief Overview

The consumption of high-calorie diets, a sedentary lifestyle, and malnutrition have become very common these days. These habits culminate in a state of chronic metabolic inflammation called metaflammation. This condition is increasing in the population and contributes to the development of several non-communicable diseases (NCDs), which comprise diseases that are not spread through infection but are typically caused by unhealthy behaviors, such as cardiovascular diseases, cancers, chronic lung illnesses, and diabetes. These lifestyle-associated diseases represent a growing public health problem that is spreading around the globe. Recently, research groups have been dedicated to unraveling the impacts of diet on health and disease. It is already known that some specific foods can have effects on inflammation. Careful selection of foods of an anti-inflammatory nature, avoiding pro-inflammatory foods, is essential for disease prevention and the maintenance of a healthy state. An anti-inflammatory diet plan consists of a pattern of eating that focuses on consuming whole, plant-based foods that are rich in healthy fats and phytonutrients, preventing cellular stresses, inhibiting the release of pro-inflammatory mediators, promoting healthy gut microbiota, and preventing surges in blood glucose. Diets can be classified as pro-inflammatory or anti-inflammatory (Figure 1). Some of these diets are discussed below.

Figure 1. Pro-inflammatory and anti-inflammatory diets and their main distribution in the world. (Stromsnes, Correas, Lehmann, Gambini, & Olaso-Gonzalez, 2021)

Pro-inflammatory Diet: The Western Diet

Since the industrial revolution in the 19th century, the population of industrialized countries has undergone drastic changes in lifestyle. Technological advances have facilitated a sedentary lifestyle and the population's access to industrially produced food. This resulted in excessive food consumption, combining a hypercaloric diet with reduced physical activity, leading to a reduction in the quality of life of the population and a greater tendency to develop diseases.

The composition of the Western dietary pattern is based on a large consumption of pre-packaged foods, refined grains, and sugars (high-sugar drinks, candy, and sweets), red and processed meat, fried foods, butter, and other high-fat dairy products, as well as a high consumption of salt, which overall contribute to weight gain and the proliferation of visceral adipose tissue. A growing body of evidence demonstrates that increased adipose tissue mass contributes directly to an increase in systemic inflammation. Adipose tissue can release pro-inflammatory factors, contributing to the development of NCDs including diabetes, heart disease, and obesity (Berg & Scherer, 2005).

Anti-Inflammatory Diets: Mediterranean, Nordic, Asian, and Chinese Traditional Diets

In 2015, National Geographic Fellow Dan Buettner determined five places across the world labeled as blue zones: Okinawa (Japan); Ogliastra Region, Sardinia (Italy); Nicoya Peninsula (Costa Rica); Ikaria (Greece); and Loma Linda (California) (Buettner, 2015). In these locations, the concentration of centenarians is higher than usual, with a low prevalence of chronic diseases or health conditions such as obesity, cancer, and cardiovascular diseases (for instance heart attacks and strokes) (Marston, Niles-Yokum, & Silva, 2021). The common characteristic of the people who lived in the blue zones is their lifestyle habits, including regular physical activity, life purpose, low stress, engagement in spirituality or religion, and engagement in family and social life. The diet adopted in these areas is based on moderate calorie intake, a plant-based diet, and moderate alcohol intake, which seems to be very relevant to explaining the longevity and low prevalence of NCDs in these populations. These observations have paved the way for several studies to be carried out with the aim of evaluating the role of diet in the prevention of inflammation and related diseases. It is worth noting that the unique genetic patterns of these populations may also contribute to their longevity and lower rates of NCDs, and researchers have taken this aspect into account in their studies.

The Mediterranean Diet (MD) is inspired by the traditional dietary patterns of countries bordering the Mediterranean Sea, such as Italy and Greece, where Sardinia and Ikaria are located, respectively, regions belonging to the blue zones. The concept of the MD was first described by Dr. Ancel Keys, who started his studies back in 1960 and observed that populations living in multiple countries in the Mediterranean region had lower rates of heart disease compared to other Western countries (Keys et al., 1986). These populations shared a diet based mainly on vegetables and moderate consumption of wine. The traditional MD is characterized by a high intake of plant foods (legumes, fruits, vegetables, nuts, and seeds), bread and unrefined cereals, olive oil (especially virgin and extra-virgin olive oil); a moderate intake of dairy products (mostly cheese and yogurt); eggs, fish, and poultry consumed in low to moderate amounts; red meat consumed in low amounts; low consumption of alcohol (red wine when consumed) (Merra et al., 2020).

Figure 2. Characteristics of Mediterranean diet. (Merra et al., 2020)

Another anti-inflammatory diet that has attracted the attention of researchers is the Nordic Diet (ND). The ND has many similarities with the MD, focusing on the abundant intake of fruits (berries, apples, pears) and vegetables (carrots, potatoes, cabbages), whole grain products, fish, and vegetable oil (canola oil instead of olive oil), limited use of saturated fat, and red and processed meat (Lankinen, Uusitupa, & Schwab, 2019).

Eastern societies are known for their extended longevity and healthy habits, including diet. For instance, one of the blue zones is in Japan, on the island of Okinawa, known as "the land of immortals". The Washoku, a traditional Japanese diet, is based on the high consumption of many types of fish and soybean products, associated with low consumption of animal fat and meat. The use of umami taste to enhance palatability prevents excessive consumption of refined sugar and salt. The use of frying is unusual, with steaming, boiling, and stewing being the main cooking methods in this diet. Portion sizes are generally small and mostly low in caloric density (Gabriel, Ninomiya, & Uneyama, 2018).

Table 1. Characteristic dishes and ingredients of the Japanese traditional diet. (Gabriel et al., 2018)

Finally, it is worth mentioning the traditional Chinese-based diet, the Jiangnan diet, consumed in some regions of China, especially in the south, where obesity and metabolic syndrome prevalence are lower. In the south of China, there is common consumption of vegetables and fruits in season, fresh fish and shrimp, and legumes; moderate consumption of whole-grain rice, plant oils (mainly rapeseed oil), red meat, and a relatively low consumption of salt. The use of soy-derived products is also frequent in this region, and steaming or boiling are the preferred cooking procedures (Wang, Lin, Bloomgarden, & Ning, 2020).

Figure 3. Jiangnan products and a representative dinner composition of Jiangnan diet. (Wang et al., 2020)

The anti-inflammatory properties of the diets discussed above are mainly attributed to the polyphenols present in fruits and vegetables, as well as cereals, legumes, and fish (to a lesser extent). Polyphenols are compounds that exhibit antioxidant properties, which means they protect our cells from damage caused by harmful molecules, such as inflammatory molecules and free radicals. The different compounds with anti-inflammatory activity and the foods with the highest concentrations of these compounds are described in Table 2.

Table 2. Representation of the main anti-inflammatory compounds and related foods. (Stromsnes et al., 2021)

Conclusions

To better understand the potential anti-inflammatory properties of a diet, it is essential to conduct comprehensive studies that analyze the dietary patterns of the population, considering genetic and environmental factors. Currently, numerous clinical trials are underway to assess the impact of diet on various diseases, including Alzheimer's disease, arthritis, cancer, infectious diseases, and more. However, examining the relationship between diet and the pathophysiology of different diseases is a complex task that requires significant investments, a qualified team of physicians and researchers, as well as the recruitment of patients for the study. Many of these studies are longitudinal, which means subjects are monitored over a period of time, which inherently requires substantial time to complete (years or decades). Furthermore, conducting multicenter studies in different geographic regions or countries is crucial for minimizing the influence of the population-specific genetic factor, as well as environmental factors, reducing the potential bias that may arise from studying a unique population.

Despite the acknowledged benefits of anti-inflammatory diets, such as the aforementioned examples, it is important to note that, in some locations, these diets have also undergone Westernization over the past few decades. Studies have shown that this shift towards a more Westernized diet has resulted in a subsequent increase in NCDs rates in those locations. On the other hand, as anti-inflammatory diets gain popularity, they have the potential to serve as lifestyle templates that can be adapted with country-specific and culturally appropriate variations in other regions, with consequent better overall health outcomes.

References

Berg, A. H., & Scherer, P. E. (2005). Adipose tissue, inflammation, and cardiovascular disease. Circ Res, 96(9), 939-949. DOI: https://doi.org/10.1161/01.RES.0000163635.62927.34

Buettner, D. (2015). The blue zones solution: Eating and living like the world's healthiest people. National Geographic Books.

Gabriel, A. S., Ninomiya, K., & Uneyama, H. (2018). The Role of the Japanese Traditional Diet in Healthy and Sustainable Dietary Patterns Around the World. Nutrients, 10(2). DOI: https://doi.org/10.3390/nu10020173

Keys, A., Menotti, A., Karvonen, M. J., Aravanis, C., Blackburn, H., Buzina, R., . . . et al. (1986). The diet and 15-year death rate in the seven countries study. Am J Epidemiol, 124(6), 903-915. DOI: https://doi.org/10.1093/oxfordjournals.aje.a114480

Lankinen, M., Uusitupa, M., & Schwab, U. (2019). Nordic Diet and Inflammation-A Review of Observational and Intervention Studies. Nutrients, 11(6). DOI: https://doi.org/10.3390/nu11061369

Marston, H. R., Niles-Yokum, K., & Silva, P. A. (2021). A Commentary on Blue Zones((R)): A Critical Review of Age-Friendly Environments in the 21st Century and Beyond. Int J Environ Res Public Health, 18(2). DOI: https://doi.org/10.3390/ijerph18020837

Merra, G., Noce, A., Marrone, G., Cintoni, M., Tarsitano, M. G., Capacci, A., & De Lorenzo, A. (2020). Influence of Mediterranean Diet on Human Gut Microbiota. Nutrients, 13(1). DOI: https://doi.org/10.3390/nu13010007

Stromsnes, K., Correas, A. G., Lehmann, J., Gambini, J., & Olaso-Gonzalez, G. (2021). Anti-Inflammatory Properties of Diet: Role in Healthy Aging. Biomedicines, 9(8). DOI: https://doi.org/10.3390/biomedicines9080922

Wang, J., Lin, X., Bloomgarden, Z. T., & Ning, G. (2020). The Jiangnan diet, a healthy diet pattern for Chinese. J Diabetes, 12(5), 365-371. DOI: https://doi.org/10.1111/1753-0407.13015

Visual Sources

Figure 1: Stromsnes, K., Correas, A. G., Lehmann, J., Gambini, J., & Olaso-Gonzalez, G. (2021). Anti-Inflammatory Properties of Diet: Role in Healthy Aging. Biomedicines, 9(8). [image]. DOI: https://doi.org/10.3390/biomedicines9080922

Figure 2: Merra, G., Noce, A., Marrone, G., Cintoni, M., Tarsitano, M. G., Capacci, A., & De Lorenzo, A. (2020). Influence of Mediterranean Diet on Human Gut Microbiota. Nutrients, 13(1). [image]. DOI: https://doi.org/10.3390/nu13010007

Figure 3: Wang, J., Lin, X., Bloomgarden, Z. T., & Ning, G. (2020). The Jiangnan diet, a healthy diet pattern for Chinese. J Diabetes, 12(5), 365-371. [image]. DOI: https://doi.org/10.1111/1753-0407.13015