1 School of Human Nutrition, McGill University, Ste Anne de Bellevue, QC.
2 Department of Medicine, Division of General Internal Medicine, McGill University, Montreal, QC.
3 Department of Medicine, Division of Clinical Epidemiology, McGill University, Montreal, QC.
4 Department of Health, Kinesiology and Applied Physiology, Concordia University, Montreal, QC.
5 Montreal Behavioural Medicine Centre, CIUSSS-NIM, Montreal, QC.

Background: Adequate nutrition is important for bone health, especially for bone mineral accretion.

Objective: The primary objective tested whether increasing dairy intake using the motivational interviewing technique (MInt) improves lumbar spine (LS) bone mineral density (BMD) after 2 years in post-pubertal adolescents with habitual dairy intake of < 2 dairy servings/day.

Design: Participants (14-18.9 y) were randomized to: Group 1 (control), group 2 (target of 3 dairy servings/d), or group 3 (target of = 4 dairy servings/d) for 12 months with groups 2 and 3 using MInt, with an additional 12-month non-intervention follow-up. The primay outcome was LS BMD, and secondary outcomes: whole body (WB), total hip (TH), and 33% distal radius BMD using dual-energy x-ray absorptiometry, bone geometry using peripheral quantitative computed tomography, and bone biomarkers.

Results: Ninety-four adolescents (16.6 ± 1.5 y) were recruited. Seventy-six (80.9%) completed the 12-month assessments. From baseline to 12 months, dairy intake in female groups 2 and 3 increased by 107% and 208%, respectively; and by 48% and 153% in males of group 2 and 3, respectively. In females, group 3 had greater increases in THBMD (4.3 to 7.5%) compared to control (3.7 to 4.9%, P = 0.04) and group 2 (0.0 to 1.7%, P = 0.04) at 12 and 24 months. No effects due to dairy intake were observed for DXA outcomes in males or radial and tibial volumetric BMD in both sexes. None of the bone biomarkers were different among the dairy groups in females or males.

Conclusion: MInt effectively increased dairy intake with benefits to bone health only in female adolescents with previously low calcium intake who consumed 4 dairy serving or more/day for 12 months. Larger studies are required to explain the lack of intervention effect in males.This trial was registered at ClinicalTrials.gov as. NCT02236871.