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It is one of the scourges of life in the modern world: chronic inflammation. This unhelpful response by the body’s immune system is linked to accelerated ageing and conditions such as stroke and heart disease.

What if we could dampen it down by consuming certain foods, such as spinach, walnuts and salmon? That is the promise of anti-inflammatory diets, often advocated in vague terms by the media and nutrition industry. That might prompt eye-rolling from the scientifically minded. But recent research reveals that this approach isn’t as faddish as it sounds and paints a nuanced picture of the links between food, inflammation and our long-term health.

Inflammation is a crucial part of our response to injury and disease. But when the body continues to deploy it even when there is no trauma, this results in chronic inflammation. Exactly why this occurs is unclear, but genetics, environment and lifestyle play roles. It can be detected by measuring certain chemical markers in the blood, and has been increasingly linked with poor health.

“Chronic inflammation is a driver of many common diseases, including cardiovascular disease, cancer, arthritis and dementia,” says at Newcastle University in the UK. It has also been implicated in some mental health conditions.

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But how much influence can our diet have on this complex process? To find out, we first have to define exactly what an anti-inflammatory diet is. “This is a disputed area,” says Mathers. “There are several competing systems for characterising pro and anti-inflammatory diets.”

Mediterranean diet

One of the most widely used metrics is the (DII), first described in 2009. This classifies foods or the nutrients in them, such as carbohydrates and saturated fats, according to their tendency to increase or decrease those chemical markers in blood. Broadly speaking, anti-inflammatory foods feature heavily in the Mediterranean diet – fresh fruit, olive oil, green leafy vegetables, nuts and oily fish – while simple carbohydrates, fried foods, red meat, processed meat and high-fat dairy are pro-inflammatory.

Many of us now eat a diet that triggers inflammation. For instance, a study published in September of more than 34,500 adults in the US found that, overall, . Worryingly, this figure was higher for Black people, men, younger adults and people with lower education and income, leading the study’s authors to conclude that “socio-economic disparities in health may be partially explained by the inflammatory potential of diet”.

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But how does this process play out in the body? Here, the picture has become clearer over the past decade. We now know that key players are the microbes in our gut, which can break down constituents of food to produce compounds that either trigger or dampen inflammation. For example, plant fibre feeds certain microbes in the large intestine, enabling them to make short-chain fatty acids, “which have anti-inflammatory effects”, says at the University of Aberdeen in the UK. “A fibre-poor diet will be more pro-inflammatory.”

A number of clinical trials have convincingly demonstrated that anti-inflammatory diets (by far the best studied being the Mediterranean diet) can . A bigger challenge, however, is working out what difference this makes to our long-term health.

Anti-inflammatory diet impacts

The best picture we have of this is from two wide-reaching reviews from 2021, focusing on studies of diets that relied on the DII, ignoring other purported anti-inflammatory versions. One found that lower-DII diets cut the chance of having a heart attack, with “highly suggestive” evidence that low-DII diets reduce the risk of certain cancers, notably colorectal, and of all-cause mortality over the study period.

For most health outcomes, however, ranging from breast cancer to depression, there was little or no evidence for benefits.

The found “moderate certainty” for low-DII diets reducing cardiovascular disease, colorectal cancer and all-cause mortality.

Another way to investigate the health impacts of anti-inflammatory diets is to think about the effects of foods that shouldn’t be in them. Growing evidence suggests, for example, that a is . But though , it is one of many, including type 2 diabetes. As a result, the diets that seem to offer protection are those already recognised as broadly healthy: low in processed foods, saturated fats, salt and sugars.

“To actually talk about an anti-inflammatory diet, you’re really talking about a dietary pattern that is generally healthy,” says at Otago University in Dunedin, New Zealand. He says the foods typically included in anti-inflammatory diets would, in any event, be recommended by “any dietitian who’s worth their salt”.

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