Nancy I. Williams is an American kinesiologist who is a professor at Pennsylvania State University. Her research considers the physiological mechanisms that underpin energy balance, exercise performance and bone health. She is a former president of the American Kinesiology Association and Fellow of the American College of Sports Medicine.

Williams is from New Jersey. She attended Shawnee High School.^[1] Williams studied biology at Bucknell University before moving to Ohio State University for a graduate degree.^[1] Williams moved to the Boston University for her doctoral research, where she focussed on anatomy and physiology.^[2] After earning her doctoral degree, Williams moved to the University of Pittsburgh, where she worked as a postdoctoral researcher in reproductive sciences.^[3]

Williams studies women's health and exercise.^[4] In 1997, Williams joined the faculty at Pennsylvania State University, where she was promoted to full professor in 2009.^[5] In 2012 Williams was made Head of Department of Kinesiology at the Pennsylvania State University College of Health and Human Development.^[6][7] Her research includes randomized controlled trials to understand the female athlete triad. She has shown that up to 60% of women recreational athletes experience menstrual dysfunction.^{[citation needed]} She has explored how weight loss impacts the acute-exercise induced suppression of appetite.^[8] She serves on the Board of Directors of the Female and Male Athlete Triad.^[9]

In 2019 Williams was elected President of the American Kinesiology Association.^[5]

• 1994 National Institutes of Health Individual National Research Service Award^{[citation needed]}
• 1998 Elected Fellow of the American College of Sports Medicine^{[citation needed]}
• 2001 Department of Defense Breast Cancer Research Program Career Development Award^{[citation needed]}
• 2011 Elected Fellow of the National Academy of Kinesiology^[10][11]

• Souza, Mary Jane De; Nattiv, Aurelia; Joy, Elizabeth; Misra, Madhusmita; Williams, Nancy I.; Mallinson, Rebecca J.; Gibbs, Jenna C.; Olmsted, Marion; Goolsby, Marci; Matheson, Gordon; Panel, Expert (2014-02-01). "2014 Female Athlete Triad Coalition Consensus Statement on Treatment and Return to Play of the Female Athlete Triad: 1st International Conference held in San Francisco, California, May 2012 and 2nd International Conference held in Indianapolis, Indiana, May 2013". British Journal of Sports Medicine. 48 (4): 289. doi:10.1136/bjsports-2013-093218. ISSN 0306-3674. PMID 24463911.
• Williams, Nancy I.; Helmreich, Dana L.; Parfitt, David B.; Caston-Balderrama, Anne; Cameron, Judy L. (2001). "Evidence for a Causal Role of Low Energy Availability in the Induction of Menstrual Cycle Disturbances during Strenuous Exercise Training". The Journal of Clinical Endocrinology & Metabolism. 86 (11): 5184–5193. doi:10.1210/jcem.86.11.8024. ISSN 0021-972X. PMID 11701675.
• De Souza, Mary Jane; Leidy, Heather J.; O’Donnell, Emma; Lasley, Bill; Williams, Nancy I. (2004). "Fasting Ghrelin Levels in Physically Active Women: Relationship with Menstrual Disturbances and Metabolic Hormones". The Journal of Clinical Endocrinology & Metabolism. 89 (7): 3536–3542. doi:10.1210/jc.2003-032007. ISSN 0021-972X. PMID 15240643.