Eating more fruits/vegetables and less dietary fat rank among the most important nutrition recommendations for health improvement. Telephone counseling is an increasingly popular means of delivering support for diet modification. Using a best-evidence synthesis, the purpose of this review was to assess the effectiveness of telephone-based counseling on improving dietary fat, fruit, and vegetable consumption for adults. Online databases and article bibliographies were searched to produce relevant randomized-controlled trials published during the past 5 years. Nine studies were ultimately included and the weight of the evidence indicated that telephone-based counseling promotes significantly greater improvements in fruit/vegetable consumption (median effect size=0.41) and dietary fat intake (median effect size=0.22) relative to usual care. Improvements were especially pronounced among women with (or at high risk for developing) cancer. In some studies, telephone-based counseling was also associated with greater improvement in blood lipid levels and weight. Based on these findings, several design considerations (eg, population focus, counseling intensity) for program managers are proposed. Telephone-based counseling was found to be a moderately effective intervention, but there are not enough studies yet to draw conclusions on other research questions, such as how advantageous telephone-based counseling is over traditional forms of dietary counseling. At present, telephone-based counseling may best be used as a complement to clinical care and a means to broaden the outreach of nutrition services.