There are many health and economic consequences for patients with osteopenia, the precursor to osteoporosis. A range of treatments may provide positive outcomes for otherwise healthy adults, including dietary and exercise approaches, either alone or in combination. The primary aim of this systematic review was to evaluate the effect of dietary approaches (including diet alone, diet with dietary supplements, both with or without physical activity intervention) on bone mineral density (BMD) to treat adults aged ≥18 years who were classified as having osteopenia. Six databases (Ovid MEDLINE including Ovid Medline in process, Cochrane Library, EMBASE, CINAHL Plus, Web of Science and Scopus) were searched systematically to identify randomised controlled trials of dietary approaches to treat osteopenic adults published from 1994 to November 2014. Study eligibility was determined, and included studies were assessed for risk of bias. Outcome data, particularly the primary outcomes of BMD T-and Z-scores or other measures of bone density, were combined narratively. The searches yielded 3511 papers, with three studies fulfilling the inclusion criteria. These studies included 254 participants, all free-living post-menopausal females with confirmed osteopenia. Vitamin D interventions were tested in all included studies, with none showing significant differences between intervention and placebo groups on BMD. This review has identified a lack of evidence to guide clinical practice in this area. Opportunities exist for future research to determine the effect of nonpharmacological approaches to osteopenia treatment in healthy populations, especially research that considers younger-aged and male populations, physical activity, habitual dietary intake and key bone health nutrients.