Summary: The dietary inflammatory index (DII) is a score which can be applied to someone’s diet to measure its probable effect on inflammation in the body. In a randomised controlled trial in patients who had experienced a heart attack, we assessed whether following a Mediterranean diet improved DII score more than a conventional low-fat diet. We found that following a Mediterranean diet significantly improved DII score, i.e. the diet lead to a more anti-inflammatory diet potential, whereas the low-fat diet did not.

Chronic low-grade inflammation in the body is recognised to contribute to the development of chronic diseases, including cardiovascular disease. The dietary inflammatory index (DII) provides a method to assess the likely impact that one’s diet is having on inflammation¹.

Why assess the DII?

The DII is calculated based on intake of 45 diet parameters (nutrients or individual foods) known to influence levels of circulating inflammatory markers, in either an anti- or pro-inflammatory manner. The score can range from -9 to +8. The more negative a person’s score the more anti-inflammatory their diet potential is, and the more positive a person’s score the more pro-inflammatory their diet potential is. The DII provides a useful alternative to measuring levels of inflammatory markers which require invasive testing, are costly and not routinely available.

What did we do?

In Australia, a low-fat diet is recommended for the prevention of cardiovascular disease. However, we hypothesised that a Mediterranean diet is likely to have a higher anti-inflammatory potential due to its composition. To test if this was true, we assessed: (1) the DII scores of an Australian Mediterranean diet model² and a low-fat diet model, and (2) if DII score improved following intervention with these two alternate diet models in 56 patients who had experienced a heart attack. This pilot study from a randomised controlled trial, conducted at La Trobe University, Melbourne, Australia, has recently been published in Nutrition Research³.

What did we find?

Firstly, we found that our Mediterranean diet model had a markedly lower (more anti-inflammatory) DII score than the low-fat diet model. The Mediterranean diet score was -4.55, whereas the low-fat diet score was -0.33. Secondly, we found that the study group who followed the Mediterranean diet intervention significantly improved their mean DII score; it became more negative from -0.4 at the start to -1.7 after 6-months. By comparison, the study group on the low-fat diet group did not significantly improve their DII score (in fact it tended to become slightly more positive) after 6-months. These changes in DII score for the diet study groups are demonstrated in the figure.

Why did the Mediterranean diet have greater anti-inflammatory potential?

The 45 diet parameters which are used to calculate DII score include a range of macronutrients, vitamins, minerals, and flavonoids (types of bioactive substances found in plant foods), as well as herbs and spices. The composition of the Mediterranean diet lends itself to a higher composition of many of the healthy diet parameters that are included in the DII, whereas a low-fat diet does not necessarily include these foods or cuisine elements. For example, both a low-fat diet and Mediterranean diet promote vegetables, fruits and wholegrains; however, the Mediterranean diet specifically promotes extra virgin olive oil, nuts, legumes, oily fish, onion, garlic, leafy greens, herbs and red wine. These specific foods which are mostly plant-based and highly nutritious contribute to the diet’s anti-inflammatory potential.

What do these findings mean?

Other studies have demonstrated that people who have a lower (more anti-inflammatory) DII score have reduced levels of inflammatory markers, as well as a reduced risk of a range of chronic diseases, including cardiovascular disease⁴. This suggests that the improvement in DII score that was achieved in heart disease patients with our Mediterranean diet intervention is likely to lead to reduced inflammation and cardiovascular complications – but, more research is needed to test whether this is true. A low-fat diet is currently recommended in practice for prevention of cardiovascular disease in Australia. However, our findings demonstrated that implementation of a Mediterranean diet, which is higher in healthy fats, plant-based foods, and herbs and spices, would be likely to achieve a greater improvement in diet quality.

This study was supported by La Trobe University (Understanding Disease RFA Start-Up Grant, 2013), an Australian Government Research Training Program Scholarship and Northern Health PhD Scholarship (Dr Mayr), Cobram Estate (extra virgin olive oil), Almond Board (almonds), Jalna Dairy Foods (Greek yoghourt), Simplot (canned fish and legumes), Heinz (canned fish and legumes), and Carman’s (muesli bars).

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