BackgroundA very low–carbohydrate (VLC) nutritional strategy may improve glycemic control and weight loss in adults with type 2 diabetes (T2D). However, the supplementary behavioral strategies that might be able to improve outcomes using this nutritional strategy are uncertain.ObjectiveThis study aims to compare the impact of adding 3 different supplementary behavioral strategies to a web-based VLC diet intervention. To our knowledge, this is the first trial to randomize participants to different frequencies of dietary self-monitoring.MethodsThe study included 112 overweight adults with T2D (hemoglobin A1c≥6.5%) taking no antiglycemic medications or only metformin. They received a remotely delivered 12-month VLC diet intervention. Participants were randomly assigned through a full factorial 2×2×2 design to supplementary strategies: either daily or monthly dietary self-monitoring, either mindful eating training or not, and either positive affect skills training or not. Our research goal was to determine whether 3 different supplemental strategies had at least a medium effect size (Cohend=0.5).ResultsOverall, the VLC intervention led to statistically significant improvements in glycemic control (−0.70%, 95% CI −1.04% to −0.35%;P<.001), weight loss (−6.82%, 95% CI −8.57% to −5.08%;P<.001), and depressive symptom severity (Cohend−0.67, 95% CI −0.92 to −0.41;P<.001). Furthermore, 30% (25/83) of the participants taking metformin at baseline reduced or discontinued their metformin. Only 1 Cohendpoint estimate reached 0.5; daily (vs monthly) dietary self-monitoring had a worse impact on depressive symptoms severity (Cohend=0.47, 95% CI −0.02 to 0.95;P=.06). None of the strategies had a statistically significant effect on outcomes. For changes in our primary outcome, hemoglobin A1c, the daily (vs monthly) dietary self-monitoring impact was 0.42% (95% CI −0.28% to 1.12%); for mindful eating, it was −0.47% (95% CI −1.15% to 0.22%); and for positive affect, it was 0.12% (95% CI −0.57% to 0.82%). Other results for daily (vs monthly) dietary self-monitoring were mixed, suggesting an increase in weight (0.98%) and depressive symptoms (Cohend=0.47), less intervention satisfaction (Cohend=−0.20), more sessions viewed (3.02), and greater dietary adherence (Cohend=0.24). For mindful eating, the results suggested a benefit for dietary adherence (Cohend=0.24) and intervention satisfaction (Cohend=0.30). For positive affect, the results suggested a benefit for depressive symptoms (Cohend=−0.32), the number of sessions viewed (3.68), dietary adherence (Cohend=0.16), and intervention satisfaction (Cohend=0.25).ConclusionsOverall, our results support the use of a VLC diet intervention in adults with T2D. The addition of monthly (not daily) dietary self-monitoring, mindful eating, and positive affect skills training did not show a definitive benefit, but it is worth further testing.Trial RegistrationClinicalTrials.gov NCT03037528; https://clinicaltrials.gov/ct2/show/NCT03037528