Table 1. Associations of dietary protein with measures of bone health in humans.

Author, year	Design	Population, n	Exposure or intervention	Outcome measure	Results	Interaction with calcium intake
Bone mineral density
Hannan et al. 2000 [7]	Longitudinal, FOP Study	Men and women; mean age 75 years; n=615	Total protein, animal protein, FFQ	Femoral neck; lumbar spine; 4-year change	Less loss over 4 years with greater protein intake	Not tested
McLean et al. 2011 [8]	Cross-sectional, FOP Study	Women; mean age 60; n=1639	Dietary acid load, FFQ	Femoral neck; lumbar spine	No associations in women	No significant interactions observed for either sex
		Men; mean age 61; n=1280			No associations in men
Mangano et al. 2013 [9▪]	Cross-sectional, NHANES	Women; mean age 69; n=907	Dietary acid load, average of two 24h recalls	Proximal femur; femoral neck; lumbar spine	Increase in proximal femur BMD with greater DAL	Significant inverse association at the proximal femur among men only, with intakes <800 mg/day
		Men; mean age 69; n=1218			No associations in men
Sukumar et al. 2011 [10]	RCT, 1-year intervention	Women; mean age 58 years; n=47	Weight loss trial: high protein diet (24%); normal protein diet (18%)	Volumetric BMD:radius; lumbar spine; total hip	High protein diet attenuated loss of BMD	Not tested
Zhu et al. 2011 [11]	RCT, 2-year intervention	Women; mean age 74 years; n=219	Whey protein supplement 30 g/day	Total hip; femoral neck	No significant differences in BMD between intervention and placebo groups	Not tested
Oh et al. 2013 [12▪]	Cross-sectional, Korean National Cohort	Women; mean age 60; n=1393	Total, animal, vegetable, dairy protein, FFQ	Calcaneal bone density, stiffness index	No significant associations	Not tested
		Men; mean age 59; n=1182			Positive association with meat protein intake
Kim et al. 2013 [13▪]	Cross-sectional, KNHANES IV	Men and women; age >19 years; n=6952	Total protein, 24h recall	Prevalence of lumbar spine osteoporosis	High protein intake associated with lower odds of osteoporosis	Not tested
Risk of falls or fracture
Sahni et al. 2010 [4]	Longitudinal; (12-year FU), FOP Study	Men and women; mean age 71 years; n=3656	Total, animal and plant protein; FFQ	Risk of hip fracture	Greater animal protein associated with reduced risk of hip fracture	High intake of animal protein associated with reduced risk among those with calcium ≥800 mg/day
Misra et al. 2011 [14]	Longitudinal (11-year FU), FOP Study	Men and women; mean age 75 years; n=946	Total protein; FFQ	Risk of hip fracture	Lower risk of fracture with greater dietary protein	Not tested
Martinez-Ramirez et al. 2012 [15▪▪]	Matched case–control study	Men and women; age ≥65 years; n=167	Total, animal, plant, animal: plant ratio; FFQ	Low impact fracture	No significant association of any type of protein with fracture	Lower animal protein intake among controls with calcium <800 mg/day
Zoltick et al. 2011 [16]	Longitudinal (1-year FU), FOP Study	Men and women; mean age 75 years; n=807	Total, animal, plant; FFQ	Risk of falls	Total and animal protein associated with reduced odds of falling among individuals with ≥5% weight loss	Not tested
Markers of bone turnover
Josse et al. 2012 [17▪]	RCT, 16 weeks	Women; age 19–45 years; n=90	Three groups: high protein, high dairy; adequate protein, medium dairy; adequate protein, low dairy	OC, PTH, P1NP, 25(OH)D	High protein high dairy group significantly increased OC, P1NP, 25(OH) D and decreased PTH	High calcium intake (1600 mg/day) in the high protein high dairy group

25(OH)D, serum hydroxy vitamin D; BMD, bone mineral density; DAL, dietary acid load; FFQ, food frequency questionnaire; FOP, Framingham Osteoporosis Study; FU, follow-up; KNHANES, Korean National Health and Nutrition Examination Survey; NHANES, National Health and Nutrition Examination Survey; OC, osteocalcin; P1NP, procollagen 1 amino-terminal propeptide; PTH, parathyroid hormone; RCT, randomized controlled trial.