Background/Objectives: Results from studies evaluating the sustainability of diets combining environmental and nutritional aspects have been diverse; thus, greenhouse gas emissions (that is, carbon footprint (CF)) of diets in line with dietary recommendations in free-living individuals warrants further examination. Here, changes in dietary CF related to changes in food choice during a weight loss trial among lactating women who received a 12-week diet intervention based on the Nordic Nutrition Recommendations (NNR) 2004 were analyzed. The objective of this study was to examine if a diet intervention based on NNR 2004 results in reduced dietary CF. Subjects/Methods: Changes in dietary CF were analyzed among 61 lactating women participating in a weight loss trial. Food intake data from 4-day weighed diet records and results from life cycle analyses were used to examine changes in dietary CF across eight food groups during the intervention, specified in the unit carbon dioxide equivalent (COsub.2eq/day). Differences in changes in dietary CF between women receiving diet treatment (D-group) and women not receiving it (ND-group) were compared. Results: There was no difference in change in dietary CF of the overall diet between D- and ND-group (P greater than 0.05). As for the eight food groups, D-group increased their dietary CF from fruit and vegetables (+0.06+ or -0.13 kg COsub.2eq/day) compared with a decrease in ND-group (-0.01+ or -0.01 kg COsub.2eq/day) during the intervention, P=0.01. Conclusions: A diet intervention in line with NNR 2004 produced clinically relevant weight loss, but did not reduce dietary CF among lactating women with overweight and obesity. Dietary interventions especially designed to decrease dietary CF and their coherence with dietary recommendations need further exploration. European Journal of Clinical Nutrition (2017) 71, 1241-1245; doi: 10.1038/ejcn.2017.63; published online 10 May 2017