The present study investigates the impact of a tailored nutrition intervention on the reduction of fat intake and on psychosocial determinants of fat intake. Furthermore, differences in impact between a family-based intervention (tailoring two family members, one adult and one child, simultaneously) and an individual-based intervention (tailoring one family member, one adult or one child) were studied. Analyses were conducted among 180 respondents, comparing 44 adolescents in the family condition with 50 adolescents in the individual condition and 44 parents in the family condition with 40 parents in the individual condition. Respondents in both conditions reported positive reactions towards the tailored fat feedback letters. Tailored fat feedback resulted in significantly more positive psychosocial determinants of fat intake and, among respondents with high fat intake at baseline, in a significant decrease in percent energy from fat. Parents in the family-based intervention group reported higher social support scores at post-test. No differences in post-test fat intake were found between the two study conditions. It is concluded that the results further illustrate the potential of tailored fat feedback, but the results do not provide evidence for superiority of family-based tailoring above individual-based tailored interventions for fat. Further research may be aimed at investigating the impact of comprehensive tailored family interventions, in which more than two family members participate.