Approximately 30% of patients experience "Long-COVID" syndrome presenting with symptoms such as cognitive difficulties ('brain fog'), fatigue, dyspnea, autonomic dysfunction, depression and anxiety, lasting beyond 12 weeks causing significant disability, and threaten health and wellbeing of millions around the world. At the current time, there is no effective treatment for long-COVID. Walnuts contain a mixture of nutrients and phytochemicals include monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and alpha-linolenic acid (ALA). Walnut consumption was directly associated with cognitive function. The investigators have shown pomegranate that share the same phytonutrient ellagitannins as walnut and mixed nuts including walnuts could increase blood microbiome metabolites of tryptophan metabolite indole propionate and serotonin levels via change of gut microbiota and therefore play an essential role in gut-brain axis including cognitive function. The proposed pilot study will include 76 adults (ages \>40 years) with diagnosis of SARS-CoV2 infection presenting with long-COVID symptoms lasting longer than 12 weeks. They will be randomized 1:1 to usual care vs. an intervention group that will include 2 oz (57g) of walnuts daily into their habitual diet for 12 weeks. The investigators will compare the improvement in symptoms of cognitive complains of "brain fog", fatigue and depression of the active intervention group vs. usual care. The outcome of the investigation of the benefit of walnut consumption will provide important novel information on using dietary sources of polyunsaturated fatty acids and phytochemicals to mitigate the common symptoms of long-COVID. This application was submitted in response to the California Walnut Commission's commodity board topic.