This study aimed to investigate the effects of prescriptive lifestyle advice with quantifiable dietary and physical goals compared to general lifestyle advice on weight and psychological outcomes in young women with overweight or obesity. A total of 203 women (body mass index 33.3_ 0.3, age 28_0.3 years) received either prescriptive or general lifestyle advice for weight loss over 12 weeks. Linear mixed models found that the prescriptive lifestyle advice group had significantly greater weight loss (4.2_ 0.4 kg vs 0.6_0.2 kg, P_0.001) compared to the general lifestyle advice group. However, the prescriptive lifestyle advice group also had greater attrition (48% vs 31%, P_0.05) compared to the general lifestyle advice group. Linear mixed models found that the prescriptive lifestyle advice group had greater improvement in psychological distress (_3.0_0.04 vs _1.1_0.01, P_0.05) and in selfesteem (3.2_0.8 vs _0.04_0.04, P_0.001) compared to the general lifestyle advice group. Changes in psychological distress and self-esteem remained significantly different between groups after correcting for weight loss. Food cravings decreased significantly over time without group differences (P_0.001 for time). Weight locus of control remained unchanged in either group (P_0.05). Drop-outs had greater baseline psychological distress (15.1_0.7 vs 12.5_0.4, P_0.01) and higher food cravings (2.42_0.07 vs 2.24_0.05, P_0.049) compared to completers. In conclusion, a prescriptive approach is associated with greater weight loss and greater improvements in psychological outcomes in young women compared to general lifestyle advice. However, these quantitative targets should be accompanied with qualitative advice on how they could be met in a variety of circumstances. ; Siew S. Lim, Robert J. Norman, Peter M. Clifton and Manny Noakes