Diet assessment methods in the nurses' health studies and contribution to evidence-based nutritional policies and guidelines

Objectives. To review the contribution of the Nurses' Health Studies (NHSs) to diet assessment methods and evidence-based nutritional policies and guidelines. Methods.We performed a narrative review of the publications of the NHS and NHS II between 1976 and 2016. Results. Through periodic assessment of diet by validated dietary questionnaires over 40 years, the NHSs have identified dietary determinants of diseases such as breast and other cancers; obesity; type 2 diabetes; cardiovascular, respiratory, and eye diseases; and neurodegenerative and mental health disorders. Nutritional biomarkers were assessed using blood, urine, and toenail samples. Robust findings, from the NHSs, together with evidence from other large cohorts and randomized dietary intervention trials, have contributed to the evidence base for developing dietary guidelines and nutritional policies to reduce intakes of trans fat, saturated fat, sugar-sweetened beverages, red and processed meats, and refined carbohydrates while promoting higher intake of healthy fats and carbohydrates and overall healthful dietary patterns. Conclusions. The long- Term, periodically collected dietary data in the NHSs, with documented reliability and validity, have contributed extensively to our understanding of the dietary determinants of various diseases, informing dietary guidelines and shaping nutritional policy.