Called the POLA index, the tool is based on the assumption that individual nutrients interact with the cells of our immune system and with the intestinal microbiome, modulating the body's immune response and, for example, affecting resistance to various types of infections, including COVID-19.

The index from Dr. Paweł Jagielski's team at the Department of Nutrition and Drug Research of the Jagiellonian University Medical College in Kraków assesses the immunomodulatory potential of the diet and identifies people whose nutrition includes numerous nutrient deficiencies relevant to the proper functioning of the immune system.

Based on the POLA index results, nutritionists and doctors will be able to recommend changes in patients' nutritional behaviour to improve immune response and reduce the risk of infection.

Dr. Jagielski, the first author of the study published in Nutrients (https://doi.org/ 10.3390/NU14204227), said: “Our index is a proposal addressed, tp among others, nutritionists whose patients or customers want to find out whether they comply with nutrition standards for ingredients related to the optimal functioning of the immune system.

“In a relatively easy way, they can propose some changes in the quantity and quality of the consumed products for the benefit of the patient's immune system. Another idea is to use the POLA index in scientific research concerning the relationship between diet and the risk of developing selected diseases, including respiratory tract infections.”

The inspiration for scientists was the COVID-19 pandemic. The dynamic increase in the frequency of SARS-CoV-2 infections initiated the global search for protective strategies against the new pathogen. Dr. Jagielski's team also dealt with this topic: from July 2020 to January 2021 the scientists conducted a research project to assess nutritional behaviour, physical activity, body composition and intestinal microbiome composition of vegetarians and people eating traditionally. 

In 2021, the study was expanded to include the influence of the above factors on the risk of developing COVID-19. The study (https://naukawpolsce.pl/en/news/news%2C91564%2Cdiet-can-reduce-risk-covid-19-polish-scientists-show.html) ended with the conclusion that a properly balanced diet can be an effective means of reducing this risk in healthy, physically active and non-obese young people.

The continuation of the project was the attempt to develop an index, based on which it would be possible to determine which nutrients, and thus which food products, were particularly important in supporting the function of the immune system, and which were detrimental.

In their work, the researchers used the current literature and previous results.

The researchers said: “Numerous studies have shown that many modifiable and non-modifiable factors affect the work of the immune system. Non-modifiable factors cannot be changed or controlled; they include genetic, age and physiological features.

“At the other extreme there are modifiable factors, which can be changed to varying degrees; they include nutritional behaviour, physical activity, body weight, sleep length and stress.

“It has been known for some time that diet components have an immunomodulatory effect. In addition, various nutritional deficiencies (both quantitative and qualitative ones) can result in changes in body weight, increased oxidative stress, inflammation and intestinal dysbiosis (intestinal microbiome disorder - ed. PAP). All these factors may translate into greater susceptibility of the body to viral infections and the more severe clinical course of some diseases.”

Ultimately, the POLA index is based on 15 nutrients and the amounts of consumed vegetables, fruits and nuts. 

Dr. Jagielski said: “It is calculated on the basis of 5 nutritional diaries.

“Depending on the obtained total points, a person is classified to one of three groups: BIM (beneficial immunomodulation), UBIM (unbeneficial immunomodulation) or HUBIM (highly unbeneficial immunomodulation).”

As for the components of the diet that the POLA index takes into account, they include fat-soluble vitamins (A, E and D), water-soluble vitamins (C and B), selected minerals (including zinc, iron, magnesium), precursors of polyunsaturated fatty acids Omega-3 and Omega-6 (linoleic acid and α-linoleic acid) and fibre. 

Dr. Jagielski said: “There is more and more scientific evidence that the optimisation of the diet in terms of immunomodulatory components can help prevent or alleviate some diseases, including viral respiratory tract infections.”

He added that this primarily includes ingredients supplied with a daily diet, not with supplements.

Although the concept of immunomodulation is well known, there were no tools that would help assess the impact of diet on the immune system. The only available similar index is DII (Dietary Inflammatory Index), which measures the inflammatory potential of the diet.

However, DII primarily evaluates anti-inflammatory or pro-inflammatory properties, while the POLA index has been designed to additionally include numerous biologically active compounds, which are mainly found in vegetables, fruits and nuts, and which are not yet included in nutritional databases, although they clearly affect the immune response.

Jagielski said: “DII is an approved tool for assessing pro-inflammatory and anti-inflammatory properties of the diet, while our goal was to develop an index that, based on the consumption of individual nutrients from food products, will measure the immunomodulatory potential of the diet, to put it simply, it will show nutritional behaviour that should ensure the optimal function of our immune system.

“The food we consume, especially vegetables, fruits, nuts, contains numerous compounds with antioxidant, antiviral, antibacterial, anti-inflammatory properties, which synergistically support the optimal function of the immune system, and in a broader aspect affect - our health.”

To confirm the effectiveness of the POLA index in practice, scientists from the Jagiellonian University Medical College verified it on a group of 95 adults, without comorbidities, on a traditional or vegetarian daily diet, and assessed their risk of developing COVID-19.

It also turned out that people on a diet with beneficial immunomodulation (BIM) - according to the POLA index - had about 80 percent lower risk of developing COVID-19 compared to people on a highly unbeneficial immunomodulation (HUBIM) diet.

The researchers said: “A healthy lifestyle, including a well-balanced diet, moderate physical activity, maintaining a proper body weight and dealing with stress, contribute to the optimal functioning of our immune system. On the other hand, many lifestyle factors, such as abnormal nutritional behaviour, smoking, alcohol abuse, obesity or insufficient sleep, can lead to a weaker immune response. 

“Our index was developed based on a similar assumption, namely that a properly balanced diet ensures the optimal functioning of the immune system, and bad eating habits contribute to impairment of its function.”

Although for now the POLA index has only been evaluated in the context of COVID-19, according to the researchers from Kraków it has a much broader use. And given that our immune system is constantly exposed to various pathogens, it can be an extremely useful tool. However, further research is needed in order to implement it in clinical practice.

Dr. Jagielski said: ”We would like the POLA index to be used to assess the immunomodulatory potential of the diet depending on the consumption of nutrients that strengthen immunity. In everyday practice, it can be used as a useful tool for nutritionists to identify people whose diet is poor in ingredients that ensure the optimal functioning of the immune system and correcting changes in their nutritional behaviour, which results in the optimal function of the immune system and reduced risk of infection. We would also like the POLA index to be used by scientists who study the relationship between diet, immune system and the occurrence of infectious respiratory diseases.”

PAP - Science in Poland, Katarzyna Czechowicz

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