title: Soy protein supplementation increases serum insulin-like growth factor-I in young and old men but does not affect markers of bone metabolism.
abstract: Recent studies suggest that soy protein (SP) protects bone in women; however, its effects on bone metabolism in men have not been investigated. Healthy men (59.2 +/- 17.6 y) were assigned to consume 40 g of either SP or milk-based protein (MP) daily for 3 mo in a double-blind, randomized, controlled, parallel design. Serum insulin-like growth factor-I (IGF-I), which is associated with higher rates of bone formation, was greater (P < 0.01) in men supplemented with SP than in those consuming MP. Serum alkaline phosphatase and bone-specific alkaline phosphatase activities, markers of bone formation, and urinary deoxypyridinoline excretion, a specific marker of bone resorption, were not different between the SP and MP groups. Furthermore, because substantial reductions in bone density occur in men at approximately 65 y of age, data were analyzed separately for men >/=65 y and those <65 y of age. The response to protein supplementation was consistent in the two age groups. The effects of SP on serum IGF-I levels suggest that SP may positively influence bone in men. Longer-duration studies examining the effects of SP or its isoflavones on bone turnover and bone mineral density and content in men are warranted.
authors.affiliation: Departments of Nutritional Sciences and Statistics, Oklahoma State University, Stillwater, OK 74078, USA.
authors.forename: Dania A
authors.initials: DA
authors.lastname: Khalil
authors.forename: Edralin A
authors.initials: EA
authors.lastname: Lucas
authors.forename: Shanil
authors.initials: S
authors.lastname: Juma
authors.forename: Brenda J
authors.initials: BJ
authors.lastname: Smith
authors.forename: Mark E
authors.initials: ME
authors.lastname: Payton
authors.forename: Bahram H
authors.initials: BH
authors.lastname: Arjmandi
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000097:blood / Q000378:metabolism; D000596:Amino Acids / Q000652:urine; D015415:Biomarkers / Q000097:blood / Q000652:urine; D015519:Bone Density / Q000187:drug effects; D001862:Bone Resorption / Q000175:diagnosis / Q000652:urine; D001842:Bone and Bones / Q000378:metabolism*; D004032:Diet / Q000592:standards; D019587:Dietary Supplements; D004311:Double-Blind Method; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D008894:Milk Proteins / Q000008:administration & dosage; D010024:Osteoporosis / Q000517:prevention & control; D030262:Soybean Proteins / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D015415:Biomarkers; D008894:Milk Proteins; D030262:Soybean Proteins; D007334:Insulin-Like Growth Factor I; C036020:deoxypyridinoline; D000469:Alkaline Phosphatase