Most people who contract Covid recover within a few weeks. But for some people, symptoms can develop later, or persist for a long time after the initial infection. A recent review of the evidence on long Covid suggests the condition affects at least 65 million people around the world, occurring after at least 10% of Covid infections, and affecting all age groups.

Common long Covid symptoms include fatigue, shortness of breath, and difficulties with memory and concentration (“brain fog”). Symptoms can worsen with physical or mental exertion. We’re still learning about long Covid, and treatment options are very limited.

Recently, some people, for example on social media, have been talking about a variety of diets as ways to manage long Covid symptoms. But what are these diets, and what does the evidence say?

The process by which the immune system protects us from harmful pathogens is called inflammation. But too much inflammation can be a bad thing. Scientists believe that many of the symptoms associated with long Covid arise from chronic inflammation.

So an anti-inflammatory diet involves avoiding foods that elicit inflammation, such as fried foods, refined carbohydrates, sugar, red and processed meats, and lard.

Instead, it focuses on foods that reduce inflammation, such as tomatoes, olive oil, green leafy vegetables, nuts, fatty fish and fruits such as strawberries and blueberries. These foods are high in antioxidants and compounds which help protect against inflammation.

Histamine is a compound released by cells, often in response to an injury or an allergic reaction. If we have hay fever or are stung by a bee, we might take an antihistamine.

Many of these symptoms are similar to those reported with long Covid. Some scientists have proposed that the increased inflammatory responses seen with long Covid could be caused by increased histamine release by dysfunctional immune cells, which we’ve seen before with other conditions.

A low histamine diet involves restricting the intake of food and drinks considered high in histamine for several weeks, before gradually reintroducing them to test tolerance. These include alcohol, fermented foods, dairy products, shellfish, processed meats and aged cheese, as well as wheat germ and a range of fruit and vegetables.

Plant-based eating refers to diets where the majority of energy is derived from plant foods, such as vegan and vegetarian diets. Plant-based diets are beneficial to markers of inflammation and may favourably alter immune function.

For example, compounds called polyphenols found in fruits and vegetables may improve the functionality and activity of natural killer cells, an immune cell that patrols the body recognising abnormal cells.

Though some long Covid sufferers have touted the benefits of a plant-based diet, its usefulness to alleviate long Covid symptoms has not yet been examined in clinical trials.

Some diets, such as a low histamine diet, are not currently backed up by enough data when it comes to the management of long Covid.

But a varied Mediterranean diet or well-managed plant-based diet can provide certain nutrients which have positive effects on immune function and may protect against chronic inflammation. That said, more research is still needed as to how these diets may affect long Covid.