in this specification , the following expressions have the meanings assigned to them below : “ galacto - oligosaccharide ” means an oligosaccharide comprising two or more galactose molecules which has no charge and no n - acetyl residue ; “ infant formula ” means a foodstuff intended for the complete nutrition of infants during the first four to six months of life . ( article 1 . 2 of the european commission directive 91 / 321 / eec of 14 may 1991 on infant formulae and follow - on formulae ); “ oligosaccharide ” means a carbohydrate having a degree of polymerisation ( dp ) ranging from 2 to 20 inclusive but not including lactose ; “ prebiotic ” means a selectively fermented ingredient that allows specific changes , both in the composition and / or activity in the gastrointestinal microbiota that confers benefits upon host well - being and health ( bouhnik et al , 2004 ); “ sialylated oligosaccharide ” means an oligosaccharide having a sialic acid residue with associated charge . suitable n - acetylated oligosaccharides include galnacα1 , 3galβ1 , 4glc and galβ1 , 6galnacα1 , 3galβ1 , 4glc . the n - acetylated oligosaccharides may be prepared by the action of glucosaminidase and / or galactosaminidase on n - acetyl - glucose and / or n - acetyl galactose . equally , n - acetyl - galactosyl transferases and / or n - acetyl - glycosyl transferases may be used for this purpose . the n - acetylated oligosaceharides may also be produced by fermentation technology using respective enzymes ( recombinant or natural ) and / or microbial fermentation . in the latter case the microbes may either express their natural enzymes and substrates or may be engineered to produce respective substrates and enzymes . single microbial cultures or mixed cultures may be used . n - acetylated oligosaccharide formation can be initiated by acceptor substrates starting from any degree of polymerisation ( dp ) from dp = 1 onwards . another option is the chemical conversion of keto - hexoses ( e . g . fructose ) either free or bound to an oligosaccharide ( e . g . lactulose ) into n - acetylhexosamine or an n - acetylhexosamine containing oligosaccharide as described in wrodnigg , t . m . ; stutz , a . e . ( 1999 ) angew . chem . int . ed . 38 : 827 - 828 . suitable galacto - oligosaccharides include galβ1 , 6gal , galβ1 , 6galβ1 , 4glc gal β1 , 6galβ1 , 6glc , galβ1 , 3galβ1 , 3glc , galβ1 , 3galβ1 , 4glc , galβ1 , 6galβ1 , 6galβ1 , 4glc , galβ1 , 6galβ1 , 3galβ1 , 4glc , galβ1 , 3galβ1 , 6gal1 , 4glc , galβ1 , 3galβ1 , 3galβ1 , 4glc , galβ1 , 4galβ1 , 4glc and galβ1 , 4galβ1 , 4galβ1 , 4glc . synthesised galacto - oligosaccharides such as galβ1 , 6galβ1 , 4glc galβ1 , 6galβ1 , 6glc , galβ1 , 3galβ1 , 4glc , galβ1 , 6galβ1 , 6galβ1 , 4glc , galβ1 , 6galβ1 , 3galβ1 , 4glc and galβ1 , 3galβ1 , 6galβ1 , 4glc , galβ1 , 4galβ1 , 4glc and galβ1 , 4galβ1 , 4galβ4glc and mixtures thereof are commercially available under the trade marks vivinal ® and elix &# 39 ; or ®. other suppliers of oligosaccharides are dextra laboratories , sigma - aldrich chemie gmbh and kyowa hakko kogyo co ., ltd . alternatively , specific glycoslytransferases , such as galactosyltransferases may be used to produce neutral oligosaccharides . suitable sialylated oligosaccharidesincludeneuacα2 , 3galβ1 , 4glc and neuacα2 , 6galβ1 , 4glc . these sialylated oligosaccharides may be isolated by chromatographic or filtration technology from a natural source such as animal milks . alternatively , they may also be produced by biotechnology using specific sialyltransferases either by enzyme based fermentation technology ( recombinant or natural enzymes ) or by microbial fermentation technology . in the latter case microbes may either express their natural enzymes and substrates or may be engineered to produce respective substrates and enzymes . single microbial cultures or mixed cultures may be used . sialyl - oligosaccharide formation can be initiated by acceptor substrates starting from any degree of polymerisation ( dp ) from dp = 1 onwards . preferably , the nutritional composition comprises 3 . 0 to 12 . 0 % of the oligosaccharide mixture , more preferably from 4 . 0 to 7 . 0 % of the oligosaccharide mixture . the nutritional composition preferably comprises at least 0 . 03 wt % of an n - acetylated oligosaccharide , at least 3 . 0 wt % of a galacto - oligosaccharide and at least 0 . 08 wt % of a sialylated oligosaccharide , more preferably at least 0 . 04 wt % of an n - acetylated oligosaccharide , at least 4 . 0 wt % of a galacto - oligosaccharide and at least 0 . 09 wt % of a sialylated oligosaccharide . a nutritional composition according to the invention preferably also comprises at least one probiotic bacterial strain . a probiotic is a microbial cell preparation or components of microbial cells with a beneficial effect on the health or well - being of the host . suitable probiotic bacterial strains include lactobacillus rhamnosus atcc 53103 obtainable from valio oy of finland under the trade mark lgg , lactobacillus rhamnosus cgmcc 1 . 3724 , lactobacillus paracasei cncm 1 - 2116 , lactobacillus reuteri atcc 55730 and lactobacillus reuteri dsm 17938 obtainable from biogaia , lactobacillus fermentum vri 003 , streptococcus salivarius dsm 13084 sold by blis technologies limited of new zealand under the designation k12 , bifidobacterium lactis cncm 1 - 3446 sold inter alia by the christian hansen company of denmark under the trade mark bb12 , bifidobacterium longum atcc baa - 999 sold by morinaga milk industry co . ltd . of japan under the trade mark bb536 , the strain of bifidobacterium breve sold by danisco under the trade mark bb - 03 , the strain of bifidobacterium breve sold by morinaga under the trade mark m - 16v , the strain of bifidobacterium ifantis sold by procter & amp ; gamble co . under the trade mark bifantis and the strain of bifidobacterium breve sold by institut rosell ( lallemand ) under the trade mark r0070 . the probiotic may be added in an amount between 10e3 and 10e12 cfu / g powder , more preferably between 10e7 and 10e12 cfu / g powder . preferably the nutritional composition according to the invention is an infant formula . the general composition of an infant formula according to the invention will now be described by way of example . the formula contains a protein source . the type of protein is not believed to be critical to the present invention provided that the minimum requirements for essential amino acid content are met and satisfactory growth is ensured . thus , protein sources based on whey , casein and mixtures thereof may be used as well as protein sources based on soy . as far as whey proteins are concerned , the protein source may be based on acid whey or sweet whey or mixtures thereof and may include alpha - lactalbumin and beta - lactoglobulin in whatever proportions are desired . the proteins may be intact or hydrolysed or a mixture of intact and hydrolysed proteins . it may be desirable to supply partially hydrolysed proteins ( degree of hydrolysis between 2 and 20 %), for example for infants believed to be at risk of developing cows &# 39 ; milk allergy . if hydrolysed proteins are required , the hydrolysis process may be carried out as desired and as is known in the art . for example , a whey protein hydrolysate may be prepared by enzymatically hydrolysing the whey fraction in one or more steps . if the whey fraction used as the starting material is substantially lactose free , it is found that the protein suffers much less lysine blockage during the hydrolysis process . this enables the extent of lysine blockage to be reduced from about 15 % by weight of total lysine to less than about 10 % by weight of lysine ; for example about 7 % by weight of lysine which greatly improves the nutritional quality of the protein source . an infant formula according to the present invention contains a carbohydrate source . any carbohydrate source conventionally found in infant formulae such as lactose , saecharose , maltodextrin , starch and mixtures thereof may be used although the preferred source of carbohydrates is lactose . preferably the carbohydrate sources contribute between 35 and 65 % of the total energy of the formula . an infant formula according to the present invention contains a source of lipids . the lipid source may be any lipid or fat which is suitable for use in infant formulas . preferred fat sources include palm olein , high oleic sunflower oil and high oleic safflower oil . the essential fatty acids linoleic and α - linolenic acid may also be added as may small amounts of oils containing high quantities of preformed arachidonic acid and docosahexaenoic acid such as fish oils or microbial oils . in total , the fat content is preferably such as to contribute between 30 to 55 % of the total energy of the formula . the fat source preferably has a ratio of n - 6 to n - 3 fatty acids of about 5 : 1 to about 15 : 1 ; for example about 8 : 1 to about 10 : 1 . the infant formula will also contain all vitamins and minerals understood to be essential in the daily diet and in nutritionally significant amounts . minimum requirements have been established for certain vitamins and minerals . examples of minerals , vitamins and other nutrients optionally present in the infant formula include vitamin a , vitamin 131 , vitamin b2 , vitamin b6 , vitamin b12 , vitamin e , vitamin k , vitamin c , vitamin d , folic acid , inositol , niacin , biotin , pantothenic acid , choline , calcium , phosphorous , iodine , iron , magnesium , copper , zinc , manganese , chloride , potassium , sodium , selenium , chromium , molybdenum , taurine , and l - carnitine . minerals are usually added in salt form . the presence and amounts of specific minerals and other vitamins will vary depending on the intended infant population . if necessary , the infant formula may contain emulsifiers and stabilisers such as soy lecithin , citric acid esters of mono - and di - glycerides , and the like . the infant formula may optionally contain other substances which may have a beneficial effect such as lactoferrin , nucleotides , nucleosides , and the like . finally , the formula will contain from 2 . 5 to 15 . 0 wt % of an oligosaccharide mixture consisting of n - acetylated oligosaccharide ( s ), galacto - oligosaccharide ( s ) and sialylated oligosaccharide ( s ) in amounts of at least 0 . 02 wt % of an n - acetylated oligosaccharide , at least 2 . 0 wt % of a galacto - oligosaccharide and at least 0 . 04 wt % of a sialylated oligosaccharide , the n - acetylated oligosaccharide ( s ) comprising 0 . 5 to 4 . 0 % of the oligosaccharide mixture , the galacto - oligosaccharide ( s ) comprising 92 . 0 to 98 . 5 % of the oligosaccharide mixture and the sialylated oligosaccharide ( s ) comprising 1 . 0 to 4 . 0 % of the oligosaccharide mixture . the infant formula may be prepared by blending together the protein source , the carbohydrate source and the fat source in appropriate proportions . emulsifiers may be added if desired . vitamins and minerals may be added at this point but are usually added later to avoid thermal degradation . any lipophilic vitamins , emulsifiers and the like may be dissolved into the fat source prior to blending . water , preferably water which has been subjected to reverse osmosis , may then be mixed in to form a liquid mixture . the liquid mixture may then be thermally treated to reduce bacterial loads . for example , the liquid mixture may be rapidly heated to a temperature in the range of about 80 ° c . to about 110 ° c . for about 5 seconds to about 5 minutes . this may be carried out by steam injection or by heat exchanger , e . g . a plate heat exchanger . the liquid mixture may then be cooled to about 60 ° c . to about 85 ° c ., for example by flash cooling . the liquid mixture may then be homogenised , for example in two stages at about 7 mpa to about 40 mpa in the first stage and about 2 mpa to about 14 mpa in the second stage . the homogenised mixture may then be further cooled to add any heat sensitive components such as vitamins and minerals . the ph and solids content of the homogenised mixture is conveniently standardised at this point . the homogenised mixture is transferred to a suitable drying apparatus , such as a spray drier or freeze drier , and converted to powder . the powder should have a moisture content of less than about 5 % by weight . the oligosaccharides may be added directly to the infant formula by dry mixing . preferably , the infant formula according to the invention is fed to the baby at every feed . the invention will now be illustrated by reference to the following examples . an example of the composition of an infant formula according to the present invention is given below . the effect of a nutritional composition according to the invention on lipogenesis and fat oxidation was investigated in germ free mice inoculated with a human baby microbiota ( hbm ). a total of 19 c3h female germ - free mice ( charles river , france ) were housed under the same environmental conditions and were fed with a standard semi - synthetic irradiated rodent diet ( reeves et al , 1993 ). at 8 weeks of age , the germ - free mice received a single dose of human baby microbiota ( hbm ) bacteria mixture and were assigned randomly to 2 groups which followed different nutritional interventions over a 2 week period . the hbm composition was previously reported ( martin et al , 2007 ). one group was kept as control , and was fed with a ‘ basal mix ’ diet containing in composition 2 . 5 % of a glucose - lactose mix ( 1 . 25 % each ) ( control group , n = 9 ). a second group of mice was fed with a diet containing 0 . 11 % n - acetylated oligosaccharides , 2 . 7 % galacto - oligosaccharides and 0 . 11 % sialylated oligosaccharides ( experimental group , n = 10 ). morning spot urines , blood plasma , and intact liver tissues were collected upon animal autopsy and snap - frozen prior to metabonomic analysis . metabonomics using high resolution spectroscopic methods with subsequent multivariate statistical analyses is a well - established strategy for differential metabolic pathway profiling and assessment of dietary intervention effects and efficacy ( martin et al , 2008 ; nicholson et al , 2005 ; rezzi et al , 2007b ; rezzi et al , 2007a ; stella et al , 2006 ). the metabolic profiles were mined with multivariate analytical methods to recover metabolic probes of oligosaccharide intervention , which serve as reference for describing and predicting groups of animals according to treatments ( table 1 ). table 1 and fig1 show that use of a nutritional composition according to the invention reduced triglyceride concentration in the liver . the control and experimental groups were compared using unpaired student &# 39 ; s t - test and the difference was statistical significant at 95 % confidence level . table 1 and fig2 show that use of a nutritional composition according to the invention also reduced lipogenesis and triacylglycerol incorporation into lipoproteins in the liver , the measure delta ct plotted on the y - axis in fig2 being the difference between the threshold cycle of the gene of interest and that of the endogenous reference gene . the decrease in expression levels in animals in the experimental group was significant at 99 . 9 % confidence level when using unpaired student &# 39 ; s t - test . higher urinary excretion of carnitine and acetyl - carnitine further showed enhancement of fatty acid oxidation ( table 1 ). these results together with higher betaine homocysteine methyl transferase metabolic activity in the liver ( table 1 ) indicated higher secretion of nascent lipoprotein particles , smaller in size and carrying less triacylglycerols . measures of triglycerides and activity of microsomal triglyceride transfer protein ( mttp ) and fatty acid synthase ( fas ) in the livers of mice in the control and experimental groups confirmed that mice in the experimental group had decreased hepatic triglycerides , lipogenic activities ( fas ) and incorporation of triglycerides into lipoproteins ( mttp ) ( fig2 ). the higher concentrations of carnitine and acetyl - carnitine and lower levels of l - aminoadipate and a - keto - isocaproate in urine of mice receiving prebiotic provide further evidence of a shift in lipid metabolism ( kliewer et al , 1997 ). in particular , carnitine is a well - characterized cofactor required for transformation of free long - chain fatty acids into acylcarnitines and their subsequent transport into the mitochondria ) matrix , where they undergo β - oxidation ( bremer , 1983 ). therefore , the results indicate enhancement of fatty acid oxidation ( table 1 ). these results show liver - specific changes in betaine hornocysteine methyl transferase ( bhmt ), metabolic pathways that closely interconnect choline , betaine and the formation of methionine from hornocysteine ( niculescu & amp ; zeisel , 2002 ). increased expression of bhmt has been reported as a potential mechanism contributing to higher apob secretion available for vldl assembly ( sparks et al , 2006 ). moreover , previous studies described that certain complex carbohydrate ( starch ) diets result in higher secretion of nascent vldl particles , smaller in size and carrying less triacylglycerols , and increased vldl apo b fractional catabolic rates ( fernandez et al , 1996 ). therefore , enhanced bhmt metabolism and lower mttp activities indicate higher apo b apoproteins synthesis and decreased transfer of lipids into nascent lipoproteins , which suggests the involvement of a similar mechanism in response to this intervention . the q y 2 value represents the predictability of the models , and relates to its statistical validity . data arc presented as area normalized intensities ( a . u .) of representative metabolite signals as means ± standard deviation ( sd ). the values for the hbm mice supplemented with prebiotics were compared to hbm control mice , *, and *** designate significant difference at 95 % and 99 . 9 % confidence level , respectively .
a nutritional composition for administration to an infant which composition comprises , on a dry matter basis , from 2 . 5 to 15 . 0 wt % of an oligosaccharide mixture consisting of n - acetylated oligosaccharide , galacto - oligasaccharide and sialylated oligosaccharide with the proviso that the composition comprises at least 0 . 02 wt % of an n - acetylated oligosaccharide , at least 2 . 0 wt % of a galacto - oligosaccharide and at least 0 . 04 wt % of a sialylated oligosaccharide and that the n - acetylated oligosaccharide comprise 0 . 5 to 4 . 0 % of the oligosaccharide mixture , the galacto - oligosaccharide comprise 92 . 0 to 98 . 5 % of the oligosaccharide mixture and the sialylated oligosacchardide comprise 1 . 0 to 4 . 0 % of the oligosaccharide mixture . the composition is useful for administration to an infant in the first six months of life to reduce the risk of obesity later in life .