Background <p>Nutritional status and lifestyle during the preconception phase, the months and years before conception, may have substantial impact on the health of the next generation. Diet quality during these years has been a neglected in previous dietary assessments.</p> Methods <p>The PREPARED study is a digital intervention with a randomised controlled trial design with the aim to assess its effectiveness on diet quality and micronutrient adequacy. Individuals with a Norwegian identification number without biological children aged 20–35 were recruited using social media platforms. Data was collected digitally using a dietary screener which was recoded into a diet quality score (DQS) and a 24-hour recall recoded into binary variables to compare adherence to the average requirement defined by the Nordic Nutrition Recommendations 2023. The intervention group received access to a digital resource where all components were created using the Determinants of Nutrition and Eating framework (DONE), with new weekly content across 6 months.</p> Results <p>From the total sample of 1374, the follow-up sample consisted of 186 participants (13.5%) (Control: 99, Intervention: 87) on DQS, and 150 (10.9%) on micronutrient adequacy. The mean difference between intervention and control in total diet quality score was + 1.0 (IQR − 3.0, 4.9) (adjusted <i>p</i> = 0.63). The results showed no improvement in diet quality or change in proportion of participants reaching average requirements between the intervention and control group.</p> Conclusions <p>We found no evidence towards having a healthier diet in any of the groups at the end of the trial, and there were no differences in proportions reaching average requirement for selected micronutrients. The substantial loss to follow-up might have had a significant impact on the results. Improving or developing strategies for recruitment and keeping retention rates is an important area for future intervention studies.</p> Trial registration <p>ISRCTN44294662 (04.02.2021).</p>