Skim milk powder enhances trabecular bone architecture compared with casein or whey in diet-induced obese rats.

OBJECTIVE: We previously showed that skim milk powder (SMP) prevents weight gain more so than casein or whey alone. Dairy foods and changes in body mass can affect bone architecture; therefore, our objective was to examine the effect of dairy proteins on bone structure in the tibia of dietary-induced obese rats.

METHODS: Twelve-week-old diet-induced obese Sprague-Dawley rats were randomized to one of six diets that varied in protein source (casein, whey, or SMP), Ca level (0.67% or 2.4%), and energy density (high-fat/high-sucrose [HFHS], or normal energy density [NE]). After 8 wk, body composition was assessed via dual energy x-ray absorptiometry and trabecular and cortical bone parameters of the tibia were assessed using micro-computed tomography and mixed model analysis.

RESULTS: Rats fed SMP with 2.4% calcium had significantly lower body mass and fat mass than all other groups. The ratio of bone volume to total volume (BV/TV) was significantly higher when the HFHS diet was supplemented with SMP and 2.4% calcium compared with whey (+66.7%) or casein (+32.6%). The HFHS diet group had 49.3% greater BV/TV compared with the NE groups. Increasing the amount of calcium resulted in a significant increase in BV/TV (188.9%) in the HFHS diet groups but not in the NE groups.

CONCLUSION: The intake of skim milk powder supplemented with calcium enhances trabecular bone architecture in obese rats consuming HFHS diet to a greater extent than with either casein or whey protein alone. Bioactive ingredients in complete dairy may contribute to these effects.