Anti-inflammation has garnered significant attention in recent years due to mounting evidence linking chronic inflammation to various diseases. Both consumers and researchers are increasingly aware of the importance of reducing inflammation for optimal health. The Dietary Inflammatory Index (DII) is a tool designed to measure the inflammatory potential of an individual's diet.
Understanding Inflammation: Acute vs. Chronic
Inflammation has two distinct phases: acute and chronic. Acute inflammation represents the body’s natural, protective response to injury and infection. In this phase, the immune system identifies a threat and initiates a response to prevent further damage. Chronic inflammation, however, is a long-term inflammatory state that has been associated with a variety of diseases.
What is the Dietary Inflammatory Index (DII)?
The Dietary Inflammatory Index (DII) is a scoring system that assigns a numerical value to 45 parameters, including individual foods, food components, and nutrients. This score indicates whether a person’s overall dietary pattern is considered pro-inflammatory or anti-inflammatory. The theoretical range of the DII is from -8.87 to +7.98, where negative scores indicate a more anti-inflammatory diet and positive scores indicate a more pro-inflammatory diet.
A more negative number is assigned to foods that contribute to anti-inflammatory benefits, while a more positive number is assigned to food components with pro-inflammatory properties. The DII emphasizes the importance of consuming nutrient-dense, whole foods rich in antioxidants, vitamins, and minerals.
History and Evolution of the DII
The development of the DII began in 2004, with the first version released in December 2009. However, this initial version had several drawbacks, including statistical bias, omission of flavonoids, and reversed scoring. A revised DII was released in 2014, quickly gaining favor as a research tool for studying diet-associated inflammation and health outcomes. The E-DII (Energy-adjusted DII) was developed later.
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The weights of the DII are published in the 2014 paper. Computing DII scores requires a nutrition database and normalizing dietary scores relative to the world standard food intake.
How the DII is Calculated
The DII calculation is based on a global database that provides a 'global daily mean intake' and 'standard deviation' for each food parameter. This database was built upon the analysis of relationships between food components and inflammation, as found in 1943 published articles. The 'global daily mean intake' and 'standard deviation' are used to calculate a Z-score for each individual's intake. This Z-score is obtained by subtracting the 'standard mean' from the reported intake amount and dividing by its standard deviation.
To adjust for potential right skewing in the data, the resulting value is then transformed into a percentile score. For a symmetric distribution centered around 0 (indicating no inflammation) and bounded between -1 (maximally anti-inflammatory) and +1 (maximally pro-inflammatory), each percentile score is doubled and then reduced by 1. This centered percentile value for each dietary parameter is then multiplied by its respective 'overall food parameter-specific inflammatory effect score' to derive the 'food parameter-specific DII score.' Finally, all of these 'food parameter-specific DII scores' are aggregated to determine the 'overall DII score' for each individual.
The DII encompasses 27 dietary components from NHANES, including carbohydrates, protein, total fat, alcohol, fiber, cholesterol, saturated fat, monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), niacin, folic acid, β-carotene, caffeine, energy, n-3 fatty acids, n-6 fatty acids, micronutrients such as vitamins (A, B1, B2, B6, B12, C, E) and minerals (Fe, Mg, Zinc, Selenium).
The DII and Chronic Diseases
The DII has been linked to many chronic diseases, including arthritis, many types of cancer, cardiovascular diseases, inflammatory bowel diseases, and diabetes. Evidence suggests that a high DII is associated with an increased risk of mortality from all causes, cancer, and cardiovascular disease, and it is also associated with an elevated risk of experiencing musculoskeletal and neurological conditions, such as joint pain, headaches, or migraines. Studies have shown that a high DII score is significantly related to BMI, hypertension and diabetes. Another study shows that DII is positively related to the inflammatory level of Japanese men, but this correlation is limited in women.
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DII and Chronic Pain
Chronic pain, defined as pain that persists or recurs for more than three months, affects approximately 20% of the global population. Recent research highlights the role of the immune system in chronic pain development, indicating that dietary factors may influence this process through immune system modulation. Dietary components can regulate the relationship between pain and inflammation, offering new avenues for pain relief. An individual's daily dietary habits are indicative of their risk for inflammation and oxidative stress. Systemic inflammation, influenced by the central nervous system, alters pain perception. Simultaneously, inflammation outside the central nervous system can increase pain sensitivity.
While some evidence suggests a connection between diet-induced inflammation and chronic pain, conclusive evidence is not yet established. The DII measures an individual's potential for dietary inflammation.
Strengths of the DII
The DII is designed to reflect all evidence from diverse populations using different research designs and dietary assessment methods. Despite having a lower weighting, the DII also incorporates evidence from experimental animals and cell cultures. Its widespread use in studies shows its effectiveness in examining the link between diet-related inflammation and diseases like heart conditions and certain cancers. The DII focuses on the nutritional value of food rather than just categorizing food types.
The new DII is improved in a number of ways. First, an improved scoring system has been applied to the forty-five ‘food parameters’, consisting of whole foods, nutrients and other bioactive compounds derived from a much larger literature review. Also, the new scoring algorithm avoids the arbitrariness resulting from using raw intake units to develop the DII by first standardizing the intake of food parameters to their corresponding world distributions and then calculating the centred percentiles. This method also dampens the effect of extreme values that otherwise could result in skewness of the DII scores. The DII is not limited to micronutrients and macronutrients, but also incorporates commonly consumed bioactive components including flavonoids, spices and tea. The overall score takes into account the whole diet, not just individual nutrients or foods. DII scoring is not dependent on specific population means or recommendations of intake; it is based on results published in the scientific literature.
Limitations of the DII
The DII is based upon an extensive literature search incorporating cell culture, animal and epidemiological studies on the effect of diet on inflammation. Because it is dependent on the published literature, there is the possibility that inclusion of significant findings is more likely than null findings. Despite this, slightly under one-third of all associations contributing to the calculation of the DII were null.
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People do not consume nutrients or even whole foods in isolation; so, while the DII does account for a large number of food parameters, the literature on which it is based tested the specific effects of dietary parameters one at a time.
Using the DII in Research
The DII is designed to be used with dietary data collected from different assessment methods. The ‘deluxe’ method would be an open-ended one providing data on all forty-five dietary parameters - e.g. either 24 h dietary recall interviews or food records.
Additional Lifestyle Changes
In addition to consuming a diet rich in anti-inflammatory foods, there are additional lifestyle changes that will make a positive impact on optimal overall health and decreased inflammation.
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