The Effect of Dietary Protein on Bone during Weight Loss: A Meta‐Analysis and Systematic Review

Abstract

The pervasiveness of obesity and excess adiposity is an ever prevalent reality amongst US adults, decreasing quality of life and predisposing individuals to metabolic dysfunction. Weight loss is an effective and widely used strategy for decreasing adiposity and improving overall metabolic health. In particular, higher protein weight loss diets (≥25% of energy from protein or ≥1.0 g/kg/day; HP) are shown to retain lean mass and decrease fat mass more than normal protein weight loss diets (<25% of energy from protein or <1.0 g/kg/day; NP). However, weight loss is also shown to significantly decrease bone quantity and the impact of a HP weight loss diet on bone is both unclear and controversial. With individual studies reporting conflicting results, either an exacerbation or an attenuation of weight‐loss induced bone loss with higher protein intakes, a recommendation for total protein intake during weight loss for the preservation of bone health is uncertain. Currently, no comprehensive analyses of randomized controlled trials have investigated the effects of HP weight‐loss diets on bone outcomes. The purpose of this systematic review and meta‐analysis was to assess the effects of HP versus NP weight loss diets (≥12 weeks) on bone mineral density (BMD) and bone mineral content (BMC) in healthy adults (≥19 years old). Two independent researchers collected and assessed a total of 1799 citations spanning the years 1969 to 2015 from multiple literary databases (Pubmed, Cochrane, CINAHL, Scopus, and Web of Science). Out of 1310 abstracts, 108 full articles were acquired for further inspection and 29 met the inclusion criteria for the systematic review. Data from 10 of the 29 studies displaying differences in total protein intake were extracted and a random‐effects model meta‐analysis was conducted (STATA/SE 12 software; StataCorp LP., College Station, TX). Collectively, this systematic review included 1,940 individuals (79.2% women, ~46 years old) actively engaged in a weight loss intervention lasting on average 6.2 ± 4.2 months. Average total protein intake during HP weight‐loss diets was 99.5 ± 13.5g (1.24 ± 0.16 g/kg BW; 26.2 ± 4.4 % of energy from protein), which was largely achieved through the consumption of mixed protein‐rich whole food sources (59% of studies). Though the majority of studies concluded a significant decrease in bone quantity following active weight loss (62%), the current meta‐analysis revealed neither an exacerbation nor an attenuation of bone loss while utilizing a HP weight loss diet (total BMD, p=0.11; total BMC p=0.42). An apparent positive effect was noted for lumbar spine with HP weight loss diets (Lumbar BMD, p=0.053, weighted mean difference: 0.007 g/cm2, 95% CI: −0.001, 0.016). In conclusion, a higher protein weight loss diet is known to favorably influence soft tissue compartments; however it does not appear to influence weight loss induced bone loss.Support or Funding InformationUSDA‐NIFA #2011‐38420‐20038 (WWC)