Modifying knowledge and attitudes through persuasive communication in health via radio has produced encouraging results for public health planners. This study's objective was to measure the effect of an educational strategy on knowledge and attitudes towards nutrition in two marginalized communities in Guadalajara, Mexico. Two communities were randomly selected. In each community a group of individuals was invited to be exposed to radio broadcasts. Using a coded and structured instrument, knowledge and attitudes towards the contents of nutritional education for health were measured before and after the intervention in both groups. Group A (n = 37) was organized and exposed to the dynamics of the radio forum throughout the 4 months during which the project lasted. Group B (n = 33) was not organized, and listened to the radio program according to its own cultural dynamics. Median knowledge and attitudes (KA) for group A was 56.8 in the pre-test and 74.1 in the post-test (W: p = -0.05). In group B the KA results were 53.0 and 59.2, respectively (W: p = -0.05). The results emphasize the advantages of the radio forum as a health communications strategy for human nutrition.