Volume 90, Issue 4, October (2003), pp. 743-750 © The Author 2003
doi:10.1079/BJN2003951

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The effect of polyunsaturated fatty acids, including conjugated linoleic acid, on calcium absorption and bone metabolism and composition in young growing rats

Owen Kelly¹, Siobhan Cusack¹, Christopher Jewell¹, Kevin D. Cashman^1,2
1Department of Food and Nutritional Sciences and
²Department of Medicine, University College, Cork, Republic of Ireland

 (Received 14 October 2002–Revised 13 May 2003–Accepted 2 June 2003)

The effect of polyunsaturated fatty acids (PUFA), in particular conjugated linoleic acid (CLA), on Ca and bone metabolism is unclear. In a 2×2 factorial design study, forty male 4-week-old rats were fed a control diet containing 70 g added fat (soyabean oil (SBO; n-6 PUFA-rich diet) or menhaden oil–safflower oil (MSO; n-3 PUFA-rich diet))/kg diet with 0 or 10 g CLA/kg for 8 weeks. Ex vivo prostaglandin E₂ biosynthesis by bone organ culture was significantly higher (P<0·001) in rats consuming SBO compared with MSO, irrespective of CLA. Addition of the CLA treatment to either diet further lowered (P<0·05) ex vivo prostaglandin E₂ production. Neither PUFA type nor CLA altered circulating or femoral mRNA levels of osteocalcin (a marker of bone formation) or insulin-like growth factor-I (a mediator of bone metabolism). While urinary pyridinium crosslinks levels (markers of bone resorption) were unaffected by CLA irrespective of PUFA type, they were significantly higher (P<0·05) in rats consuming SBO compared with MSO irrespective of CLA. Net fractional (%) and absolute (mg) Ca absorption were significantly (P<0·01 and P<0·05 respectively) higher in CLA-supplemented than unsupplemented animals fed on the n-3 PUFA-rich diet, whereas CLA had no effect in animals fed the n-6 PUFA-rich diet. There was no effect of CLA supplementation on bone mineral mass. In conclusion, CLA supplementation over 8 weeks appeared to enhance Ca absorption in young growing rats fed an n-3 PUFA-rich diet, but had no measurable effect on bone metabolism or bone mass over this time frame.

Keywords:
Calcium absorption, Bone metabolism, Conjugated linoleic acid, Polyunsaturated fatty acid

Abbreviations:
CLA, conjugated linoleic acid, GAPDH, glyceraldehyde phosphate dehydrogenase, IGF, insulin-like growth factor, MSO, menhaden oil–safflower oil, PG, prostaglandin, PUFA, polyunsaturated fatty acid, SBO, soyabean oil