Effect of chronic consumption of nuts on oxidative stress: a systematic review of clinical trials.

Nuts consumption has been associated with a protective effect against cardiovascular diseases and oxidative stress-related disorders. We aimed to perform a systematic review with clinical trials to assess the impact of chronic nuts consumption on oxidative stress and the possible mechanisms involved. Studies were identified by searching in three electronic databases: PubMed/MEDLINE, Scopus, and LILACS, and selected following PRISMA guidelines. Two authors perform searching and data extraction. A total of 16 articles were included (12 randomized clinical trials and 4 one or two-arm clinical trials). Nut doses were generally high (> 30 g/d), except for Brazil nuts (5-13 g/d). The follow-up time ranges between four weeks and six months, and the oxidized low-density lipoprotein (ox-LDL) was the most assessed biomarker. Eight articles reported improvement in oxidative stress biomarkers after nuts supplementation. Pathways regulated by selenium (e.g. glutathione peroxidase activity and nuclear factor-E2-related factor 2 (Nrf2) regulation), monounsaturated fatty acids (e.g. reduction of LDL oxidation), and bioactive compounds (e.g. antioxidant activity) were described as mechanisms involved in these beneficial effects. No studies reported harmful effects of nut consumption, even in high doses. The chronic consumption of nuts seemed to be effective to change some oxidative stress biomarkers, however, this topic remains controversial because the benefits depends on nut type, nut dose, and population characteristics.