Effects of dietary phytase on body weight gain, body composition and bone strength in growing rats fed a low-zinc diet B James P. McClung a,1,2 , Chad H. Stahl b,1 , Louis J. Marchitelli a , Nelson Morales-Martinez a , Katherine M. Mackin a , Andrew J. Young a , Angus G. Scrimgeour a, T a Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine (USARIEM), Natick, MA 01760, USA b Department of Animal Science, Iowa State University, Kildee Hall, Ames, IA 50011, USA Received 10 May 2005; received in revised form 30 June 2005; accepted 12 July 2005 Abstract Phytic acid, a major phosphorous storage compound found in foodstuffs, is known to form insoluble complexes with nutritionally essential minerals, including zinc (Zn). Phytases are enzymes that catalyze the removal of these minerals from phytic acid, improving their bioavailability. The objective of the present study was to determine the ability of dietary phytase to affect body weight, body composition, and bone strength in growing rats fed a high phytic acid, low Zn diet. Rats (n = 20) were fed either a control (AIN-93) or phytase supplemented (Natuphos, BASF, 1,500 phytase units (FTU)/kg) diet for a period of 8 weeks. Phytase supplementation resulted in increased (P b .05) bone and plasma Zn, but no change in plasma inorganic phosphorous or bone levels of Ca, Fe, or Mg. The addition of phytase to the diets resulted in a 22.4% increase (P b .05) in body weight at the end of the study as compared with rats fed a control diet. Dual x-ray absorptiometry (DXA) revealed that phytase supplementation resulted in increase lean body mass (LBM, P b .001) and increased bone mineral content (BMC, P b .001) as compared with feeding the control diet. Bone studies indicated that femurs and tibias from phytase supplemented rats had greater mass (P b .05) and were stronger (P b .05) than rats fed the control diet. This data suggest that the addition of phytase to low Zn diets results in improved Zn status, which may be responsible for beneficial effects on growth, body composition, and bone strength. D 2006 Elsevier Inc. All rights reserved. Keywords: Phytase; Zinc; Dual X-ray absorptiometry; Bone strength; Rats 1. Introduction Phytic acid (PA, myo -inositol hexakisphosphate) is a major phosphorous (P) storage compound found in cereals, legumes and seeds [1]. The structure of PA includes six ionizable protons that allow for the formation of insoluble complexes with multivalent cations, including calcium (Ca), zinc (Zn), copper (Cu), magnesium (Mg) and iron (Fe) [2,3]. The ability of PA to form insoluble complexes with these nutritionally essential minerals results in diminished bioavailability. In particular, Zn bioavailability is diminished by PA [4–6], and numerous reports have demonstrated reduced Zn absorption and status in animals consuming feed with high levels of PA [7–9]. Further- more, high-PA diets have been associated with reduced Zn status in humans [10,11]. The implications of dimin- ished Zn status due to poor dietary bioavailability are severe, as Zn is an essential trace element known to incor- porate into over 300 proteins, including those responsible for DNA and RNA replication, protein synthesis and gene transcription [12]. Phytases are phosphohydrolases that catalyze the removal of P and other multivalent cations from PA [13]. Many mammals, including rats, pigs and humans, have endogenous phytase activity within the small intestine, 0955-2863/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jnutbio.2005.07.003 B The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. Any citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement of approval of the products or services of these organizations. T Corresponding author. Tel.: +1 508 233 5155; fax: +1 508 233 4869. E-mail address: angus.scrimgeour@us.army.mil (A.G. Scrimgeour). 1 These authors contributed equally to this work. 2 This research was performed while the author held a National Research Council Research Associateship Award at USARIEM. Journal of Nutritional Biochemistry 17 (2006) 190 – 196