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

Abstract

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 PUFArich 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 E 2 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 E 2 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.Calcium absorption: Bone metabolism: Conjugated linoleic acid: Polyunsaturated fatty acid While dietary factors, such as Ca, Mg, Na, Cu, non-digestible oligosaccharides and vitamins D and K, amongst others, have attracted considerable attention

Effect of dietary supplementation with conjugated linoleic acid on markers of calcium and bone metabolism in healthy adult men

“…For example, Li et al (1999) showed that CLA supplementation (10 g/kg diet) of young growing male rats reduced bone mineralization, possibly by reducing the biosynthesis of PGE 2 by bone, while Kelly et al (2003) found no effect of CLA supplementation, at the same dietary level, on markers of bone formation or bone resorption in young growing male rats, despite a reduction in biosynthesis of PGE 2 . Kelly & Cashman (2004) however, report that CLA reduced markers of bone resorption (urinary pyridinium crosslinks) in ovariectomized rats.…”

“…Watkins et al (1997) found that a dietary source of anhydrous butterfat (a rich natural source of CLA) stimulated the rate of bone formation in young growing chicks. Similarly, the effect of CLA on bone mass, ash or mineral content in studies with experimental animals is also conflicting, with some studies showing an increase with CLA ( (pigs)), while others found no effect (Li et al, 1999;Kelly et al, 2003;Kelly & Cashman, 2004 (rats) and Demaree et al, 2002;Ostrowska et al, 2003 (pigs)). As already mentioned, CLA is a collective term describing a mixture of positional and geometric isomers of linoleic acid, with conjugated double bonds, which may be of cis or trans configuration at positions 9 and 11 or 10 and 12 (Lawson et al, 2001).…”

“…In experimental rats, dietary supplementation with CLA lowered ex vivo PGE 2 production in bone organ culture from ovariectomized rats as well as reducing the levels of urinary pyridinium crosslinks (markers of bone resorption) (Kelly & Cashman, 2004). In young rats, on the other hand, CLA supplementation, while lowering ex vivo PGE 2 production in bone organ culture, either reduced (Li et al, 1999) or had no effect on markers of bone formation (Kelly et al, 2003), and had no effect on markers of bone resorption (Kelly et al, 2003). CLA supplementation did, however, significantly increase the efficiency of intestinal Ca absorption in the young rats fed a n-3 polyunsaturated fatty acids (PUFA)-rich diet (Kelly et al, 2003).…”

“…There has been no other report of the effect of CLA on Ca metabolism in humans. Kelly et al (2003) recently showed that CLA supplementation (containing cis-9,trans-11 and trans-10,cis-12 CLA isomers in a 50:50 ratio) significantly increased the efficiency of intestinal Ca absorption in young growing rats fed a n-3 PUFA-rich diet, but not in rats fed a n-6 PUFA-rich diet. A preliminary investigation of the dietary ratio of n-3 to n-6 fatty acids in a subset of subjects (n ¼ 30) participating in the present study showed that the diet was rich in n-6 fatty acids (B8.6:1 n-6:n-3), which may have limited any potential stimulatory effect of CLA on intestinal Ca absorption.…”

“…In young rats, on the other hand, CLA supplementation, while lowering ex vivo PGE 2 production in bone organ culture, either reduced (Li et al, 1999) or had no effect on markers of bone formation (Kelly et al, 2003), and had no effect on markers of bone resorption (Kelly et al, 2003). CLA supplementation did, however, significantly increase the efficiency of intestinal Ca absorption in the young rats fed a n-3 polyunsaturated fatty acids (PUFA)-rich diet (Kelly et al, 2003). This effect on Ca absorption in experimental animals has been confirmed in studies using the human intestinallike Caco-2 cell model (which has been shown to be a useful in vitro model for predicting Ca absorption in human subjects; Fleet & Wood, 1999).…”