studies that examined the efficacy of plant sterols / stanols as cholesterol lowering agents in humans were identified by searching five databases pubmed , embase , medline , cochrane library and web of science using the terms  plant sterol  ,  plant stanol  ,  phytosterol  and  phytostanol  as words in the title , abstract or keywords . in addition , a manual search using reference lists of review articles ( 35 , 39 ) was performed . for non - english language literature , if available , the abstract written in english was used to extract the required information ; otherwise the trial was not included in the analysis . all citations were exported into reference manager software ( endnote version 8.0.2 ) and studies on plant sterols / stanols and cholesterol metabolism were identified . fifty - nine eligible randomized clinical trials published from 1992 to 2006 were identified from the five databases . randomized placebo controlled studies conducted to test the efficacy of plant sterols / stanols incorporated into food matrices on circulating cholesterol levels in adults were included in this meta - analysis . therefore , studies were first excluded from the meta - analysis for not measuring circulating ldl levels as a primary or secondary outcome , for having duration of intervention of less than two weeks , for examining children or adults who were homo- or heterozygote for sitosterolemia or who possessed a history of cardiovascular disease . studies were also excluded for having a co - intervention that could not be separated from plant sterol / stanol treatment , for incorporating plant sterols / stanols in the form of capsule or tablets , or for not having a control group or an appropriate control / placebo . in addition , studies were excluded if lipid profiling was done on non - fasting blood samples or if lipid profile data were published elsewhere . a total of 84 clinical trials met the first inclusion criteria and were then screened for the quality criteria ( fig . 1 ) . selection of randomized placebo controlled studies for meta - analysis of plant sterols and circulating cholesterol levels . randomized controlled studies were assessed for methodological quality with the jadad score as described in table 1 
 ( 40 ) . a jadad score of three or above , out of a maximum of five , was used to indicate that a study is of reasonable quality to be included in the meta - analysis ( 41 ) . calculation of jadad score to assess study quality . 
								 adapted from jadad et al . no data were directly obtained from the original authors . for studies that met the inclusion criteria and that possessed a jadad score of equal or more than three , data were extracted for parameters related to ( i ) trial design ; ( ii ) type of plant sterols / stanols ; ( iii ) dose ( g / day ) and duration of plant sterol / stanol treatment ; ( iv ) frequency and time of intake of plant sterols / stanols ; ( v ) food food carrier , to which plant sterols / stanols were incorporate ; ( vi ) characteristics of the study population ; ( vii ) the mean values and the standard deviations ( sd ) of ldl cholesterol levels ; and ( viii ) sample size . two reviewers ( ssa and rb ) independently identified articles for inclusion , assessed quality and extracted data . for studies that reported multiple time points for the same subjects , only endpoints for the longest duration of the intervention were used . for studies in which the outcomes were presented as percentage change from baseline , and no endpoint data were available ( 37 , 42 , 43 ) , endpoint data were imputed using the baseline values and percentage change from baseline and the sd of the baseline data for the endpoint sd . where studies reported absolute change from baseline and no endpoint data were available ( 26 , 44 , 45 ) , we imputed endpoints using baseline plus change for the mean and using the sd of the baseline data for the endpoint sd . the primary outcome for this meta - analysis was the difference in ldl cholesterol levels , reported in mmol / l , due to plant sterol / stanol treatment . for parallel arm designed trials , endpoint ldl cholesterol in the treatment group was subtracted from endpoint ldl cholesterol in the control group ( 46 ) . we did not use differences in changes from baseline as the primary outcome because this would imply imputing sds for changes from baseline for the majority of parallel studies , which is not recommended ( 46 ) . for crossover trials , the ldl cholesterol value at the end of the treatment period was subtracted from that at the end of the control period ( 46 ) . within - individual changes sds were extracted from the studies or , if not reported , derived from standard errors ( ses ) of mean , confidence intervals ( cis ) , paired t - value or p - value as provided ( 46 ) . if different treatments were tested within the same trial , they were evaluated as separate strata , as is described by  a , b , c and d  suffixes in tables and figures . to obtain the pooled treatment effect size ( es ) , es estimates and se were entered into revman 4.2 under the  generic inverse variance  outcome . a p - value  <  0.1 was used to indicate that significant heterogeneity was present ( 46 ) . estimates of the pooled treatment es of plant sterol / stanol containing food on ldl cholesterol levels and 95% cis were calculated by using both fixed effect and random effect models . if the test for heterogeneity was significant , we presented the results of the random effect models . we presented the es as mmol / l , and not as percentage difference , as most of the studies did not report the sd of the percentage difference in ldl values between the control and the treatment group or phases . the presence of publication bias was examined for using a funnel plot , in which the ses of the studies were plotted against their corresponding ess . studies that examined the efficacy of plant sterols / stanols as cholesterol lowering agents in humans were identified by searching five databases pubmed , embase , medline , cochrane library and web of science using the terms  plant sterol  ,  plant stanol  ,  phytosterol  and  phytostanol  as words in the title , abstract or keywords . in addition , a manual search using reference lists of review articles ( 35 , 39 ) was performed . for non - english language literature , if available , the abstract written in english was used to extract the required information ; otherwise the trial was not included in the analysis . all citations were exported into reference manager software ( endnote version 8.0.2 ) and studies on plant sterols / stanols and cholesterol metabolism were identified . fifty - nine eligible randomized clinical trials published from 1992 to 2006 were identified from the five databases . randomized placebo controlled studies conducted to test the efficacy of plant sterols / stanols incorporated into food matrices on circulating cholesterol levels in adults were included in this meta - analysis . therefore , studies were first excluded from the meta - analysis for not measuring circulating ldl levels as a primary or secondary outcome , for having duration of intervention of less than two weeks , for examining children or adults who were homo- or heterozygote for sitosterolemia or who possessed a history of cardiovascular disease . studies were also excluded for having a co - intervention that could not be separated from plant sterol / stanol treatment , for incorporating plant sterols / stanols in the form of capsule or tablets , or for not having a control group or an appropriate control / placebo . in addition , studies were excluded if lipid profiling was done on non - fasting blood samples or if lipid profile data were published elsewhere . a total of 84 clinical trials met the first inclusion criteria and were then screened for the quality criteria ( fig . 1 ) . selection of randomized placebo controlled studies for meta - analysis of plant sterols and circulating cholesterol levels . randomized controlled studies were assessed for methodological quality with the jadad score as described in table 1 
 ( 40 ) . a jadad score of three or above , out of a maximum of five , was used to indicate that a study is of reasonable quality to be included in the meta - analysis ( 41 ) . calculation of jadad score to assess study quality . 
								 adapted from jadad et al . no data were directly obtained from the original authors . for studies that met the inclusion criteria and that possessed a jadad score of equal or more than three , data were extracted for parameters related to ( i ) trial design ; ( ii ) type of plant sterols / stanols ; ( iii ) dose ( g / day ) and duration of plant sterol / stanol treatment ; ( iv ) frequency and time of intake of plant sterols / stanols ; ( v ) food food carrier , to which plant sterols / stanols were incorporate ; ( vi ) characteristics of the study population ; ( vii ) the mean values and the standard deviations ( sd ) of ldl cholesterol levels ; and ( viii ) sample size . two reviewers ( ssa and rb ) independently identified articles for inclusion , assessed quality and extracted data . for studies that reported multiple time points for the same subjects , only endpoints for the longest duration of the intervention were used . for studies in which the outcomes were presented as percentage change from baseline , and no endpoint data were available ( 37 , 42 , 43 ) , endpoint data were imputed using the baseline values and percentage change from baseline and the sd of the baseline data for the endpoint sd . where studies reported absolute change from baseline and no endpoint data were available ( 26 , 44 , 45 ) , we imputed endpoints using baseline plus change for the mean and using the sd of the baseline data for the endpoint sd . the primary outcome for this meta - analysis was the difference in ldl cholesterol levels , reported in mmol / l , due to plant sterol / stanol treatment . for parallel arm designed trials , endpoint ldl cholesterol in the treatment group was subtracted from endpoint ldl cholesterol in the control group ( 46 ) . we did not use differences in changes from baseline as the primary outcome because this would imply imputing sds for changes from baseline for the majority of parallel studies , which is not recommended ( 46 ) . for crossover trials , the ldl cholesterol value at the end of the treatment period was subtracted from that at the end of the control period ( 46 ) . within - individual changes sds were extracted from the studies or , if not reported , derived from standard errors ( ses ) of mean , confidence intervals ( cis ) , paired t - value or p - value as provided ( 46 ) . if different treatments were tested within the same trial , they were evaluated as separate strata , as is described by  a , b , c and d  suffixes in tables and figures . to obtain the pooled treatment effect size ( es ) , es estimates and se were entered into revman 4.2 under the  generic inverse variance  outcome . a p - value  <  0.1 was used to indicate that significant heterogeneity was present ( 46 ) . estimates of the pooled treatment es of plant sterol / stanol containing food on ldl cholesterol levels and 95% cis were calculated by using both fixed effect and random effect models . if the test for heterogeneity was significant , we presented the results of the random effect models . we presented the es as mmol / l , and not as percentage difference , as most of the studies did not report the sd of the percentage difference in ldl values between the control and the treatment group or phases . the presence of publication bias was examined for using a funnel plot , in which the ses of the studies were plotted against their corresponding ess . fifty - nine studies comprising 95 relevant strata were assessed as eligible for meta - analysis with > 4500 subjects . a summary of trial design and characteristics is shown in table 2 and table 3 . nr  =  not reported , nc  =  not clear , tx  =  treatment ; co  =  control ; w  =  women ; m  =  men . features of plant sterol intervention of randomized controlled studies of plant sterols / stanols . time of consumption of plant sterol / stanol enriched products . individual trial results and the pooled es for all trials plant sterol / stanol consumption decreased ldl levels by 0.31 mmol / l ( 95% ci , 0.35 to 0.27 , p=  <  0.0001 ) compared with placebo . between trial heterogeneity was evident ( chi - square test , p  =  < 0.0001 ; i 
				 = 65% ) . it was estimated that as 65% of the variability in the es is due to heterogeneity between the trials ( clinical and methodological diversity ) rather than chance . thus , we performed a subgroup analysis according to predefined criteria by subjects characteristics and study design features as summarized in table 4 . therefore , subjects were grouped into two groups , one included subjects with high baseline levels of ldl and the other group included subjects with low baseline levels of ldl , as defined according to atpiii ( 85 ) . a greater decrease in ldl levels was observed in subjects with optimal to borderline high levels of baseline ldl . the ldl cholesterol levels of the former decreased by 0.37 mmol / l ( 95% ci : 0.42 , 0.31 ) and those of the latter decreased by 0.28 mmol / l ( 95% ci : 0.31 , 0.25 ) . the placebo adjusted reduction in ldl levels produced by consumption of plant sterols was the same across all age groups . effect size and 95% ci in ldl cholesterol levels associated with consumption of plant sterol / stanol containing food products . pooled estimates of treatment effect on ldl cholesterol in subgroups of trials defined by subject characteristics and study design features there was evidence of a dose response effect . the minimum ( 0.25 mmol / l ; 95% ci : 0.32 , 0.18 ) and the maximum ( 0.42 mmol / l ; 95% ci : 0.46 , 0.39 ) reductions in ldl cholesterol levels were achieved by the intake of < 1.5g/ day and > 2.5 g/ day of sterols / stanols , respectively . 0.32mmol / l ( 95% ci : 0.36 , 0.28 ) for intakes of 1.52.0 g / d and 2.12.5 g / d , respectively . the effect of plant sterols / stanols on ldl cholesterol is influenced by the food carrier to which plant sterols / stanols are incorporated . we predefined the food product groups according to their fat content , i.e. low fat products contain 3 g or less fat per serving , as well as their physical form , i.e. liquid versus solid . therefore , we ended up with four groups , i.e. fat spreads , mayonnaise and salad dressing , milk and yoghurt , and other food group . other food products subgroup included studies testing the efficacy of plant sterols / stanols incorporated in chocolate and cereal bars , beverages , juices , meat and croissants and muffins . all these were included in one subgroup and not further analyzed because of an insufficient number of clinical trials . plant sterols / stanols incorporated into fat spreads , mayonnaise and salad dressing or milk and yoghurt reduced ldl cholesterol levels to a greater extent than plant sterols / stanols incorporated into other food products . compared to control , ldl levels were reduced by 0.33 ( 95% ci , 0.38 to 0.28 ) , 0.32 ( 95% ci , 0.40 to 0.25 ) , 0.34 ( 95% ci , 0.40 to 0.28 ) and 0.20 ( 95% ci , 0.28 to 0.11 ) mmol / l in the fat spreads , mayonnaise and salad dressing , milk and yoghurt , and other food products , respectively . other food product subgroups included studies testing the efficacy of plant sterols / stanols incorporated in chocolate ( 47 , 48 ) , orange juice ( 22 , 23 ) , cheese ( 49 ) , non - fat beverage ( 26 , 27 ) , meat ( 33 ) , croissants and muffins ( 21 ) , oil in bread ( 43 ) , and cereal bars ( 24 ) . the favorable effect of plant sterols / stanols on ldl cholesterol levels was also shown to be influenced by the frequency and time of intake of plant sterols . for instance , plant sterols / stanols consumed 23 times / day reduced ldl cholesterol levels by 0.34 mmol / l ( 95% ci : 0.38 , 0.18 ) while plant sterols / stanols consumed once per day in the morning did not result in a significant reduction in ldl levels . on the other hand , plant sterols / stanols consumed once / day with lunch or the principal meal reduced ldl levels by 0.30 mmol / l ( 95% : 0.39 , 0.21 ) . we found no evidence of publication bias in this meta - analysis , as indicated by the funnel plot symmetry ( fig . the present meta - analysis is the first systematic quantitative review of randomized clinical trials yielding information on factors that might affect efficacy of plant sterols / stanols as cholesterol lowering agents . since the meta - analyses of law ( 4 ) and katan et al . ( 5 ) examining plant sterol / stanol effects on circulating cholesterol levels , several studies have been conducted examining the action of various plant sterol / stanol containing products on blood cholesterol levels using different study designs . the present work shows that the intake of plant sterol / stanol containing food products was associated with a significant decrease in ldl cholesterol ( 0.31 however , the substantial heterogeneity among individual trials indicates that the effects of plant sterols / stanols on ldl cholesterol levels are not uniform . a larger reduction in ldl cholesterol levels was observed in subjects with a high to very high baseline levels of ldl , compared to those with optimal to borderline high baseline levels . some previous ( 35 , 36 ) , but not other studies ( 8 , 37 , 38 ) , have reported that the higher the baseline levels of ldl - cholesterol the more the reduction in ldl due to plant sterols consumption . the present meta - analysis has confirmed that baseline ldl cholesterol levels affect magnitude of reduction in ldl after plant sterol / stanol consumption which could explain the wide variation in responsiveness seen in previous studies . nevertheless , plant sterols / stanols do reduce ldl levels in individuals with normal to high baseline ldl levels as well as in adults across different age groups . therefore , everyone , excluding individuals with -sitosterolemia and heterozygote for the disease , can reduce his / her blood cholesterol levels by consuming plant sterols / stanols . a positive dose response relationship was apparent with the greatest reduction in ldl levels obtained with intakes of 2.5 g / day of plant sterols / stanols . ( 5 ) showed that there is little additional effect of plant sterols / stanols at doses higher than 2.5 g / day . it should be noted that studies included in the subgroups with intakes 2.1 g / day incorporated plant sterols / stanols mainly in fat spreads , while the other subgroups included a variety of food products , which could explain why heterogeneity was absent with intakes of 2.1g / day . plant sterols / stanols reduce ldl cholesterol through interfering with cholesterol absorption ( 9 , 5052 ) . because of their inert crystalline structure , pure plant sterols / stanols are not consistently effective in lowering cholesterol absorption . thus , plant sterols / stanols should be adequately formulated before use . the most accepted method used to optimize the effect of plant sterols / stanols on cholesterol absorption is esterification to fatty acids and dissolving plant sterols / stanols within food fats ( 53 ) . some studies have shown that free plant sterols / stanols when mixed with fat spread are also effective in reducing ldl cholesterol levels ( 51 , 54 ) . later on , plant sterols / stanols were added to low and non - fat food products . the results presented here show that compared with plant sterol / stanol containing fat spreads , mayonnaise and salad dressing , and milk and yoghurt , other plant sterol / stanol containing food products , including chocolate ( 47 , 48 ) , orange juice ( 22 , 23 ) , cheese ( 49 ) , non - fat beverage ( 26 , 27 ) , meat ( 33 ) , croissants and muffins ( 21 ) , oil in bread ( 43 ) , and cereal bars ( 24 ) demonstrated less of a ldl - reduction efficacy . this finding highlights the importance of food carrier and proper formulation of plant sterols / stanols . although milk and yoghurt drinks contain much less fat than fat spreads and mayonnaise , milk and yoghurt drinks demonstrated similar efficacy as of products with higher fat content . thus , the food carrier to which plant sterols / stanols are added does not have to contain a high fat content to be an effective means of release of plant sterols / stanols to compete with cholesterol absorption , given that a proper plant sterol formulation is provided . unfortunately , exact methods used to formulate plant sterols / stanols in the milk and yoghurt studies are not described in adequate detail . studies were reported only if they used free ( 15 , 17 ) or esterified ( 16 , 1820 , 34 ) sterols or stanols . it is also possible that plant sterols / stanols in milk may be more readily incorporated into milk globule membranes , thus more readily compete with cholesterol for transfer into the micelles , while in the other low fat foods plant sterols / stanols may be trapped in the center of the lipid droplets and not be available until the fat is digested ( 30 ) . future work is needed to identify proper formulation of plant sterols / stanols to improve their efficacy in food products other than those with high fat contents , i.e. vegetable and dairy spreads and mayonnaise , or milk and yoghurts . in a previous study from our group , consumption of a single dose of different preparations of plant sterols in the morning failed to lower ldl levels ( 32 ) . some studies have shown that consumption of single dose of plant sterols / stanols with lunch lowered ldl levels ( 31 , 33 ) . one study has tested the efficacy of plant stanol consumed at different frequencies . in the study by plat ( 31 ) subjects consumed the plant stanol enriched margarine at breakfast and at lunch and ate a cake or cookie containing plant stanol - enriched shortening within one hour after supper . the higher portion of plant stanol during the 3 times / day phase was given using a different food carrier and was consumed without a meal in comparison to the single dose phase , thus , multiple factors might contribute to the differences in results obtained between the study phases . additionally , the availability of plant stanol in the cakes and cookies might be affected by baking conditions . to what extent this affected the cholesterol lowering action of 3 times / day phase of plant stanol intake is unknown . to examine that question , we conducted a subgroup analysis looking at frequency and time of intake of plant sterols / stanols . the results of this meta - analysis show that the time of intake of a single dose of plant sterols / stanols may affect their cholesterol - lowering action as consumption of single dose with lunch or main meal , but not before or with breakfast , lowered ldl levels . the results of the subgroup analyses examining time of intake of plant sterols / stanols should be interpreted with caution , however . the number of subjects included in the individual subgroups was small and many of the included studies did not report data on time of intake , resulting in the potential to be misled by bias . the exact mechanisms responsible for the effects of plant sterols / stanols on ldl levels are still being investigated . based on current knowledge , plant sterols / stanols reduce solubilization of cholesterol in micelles and also may affects the site of absorption and intra - cellular trafficking of cholesterol ( 55 ) . the efficacy of plant sterols / stanols as a cholesterol - lowering agent may demonstrate a time - of - day variation , possibly coinciding with the diurnal rhythm of cholesterol metabolism . diurnal rhythm in cholesterol synthesis has been shown in humans ( 5658 ) , where cholesterol fractional synthetic rate values peaked at 6:00 h and were lowest during the daytime period . moreover , bile acid synthesis in humans has also a diurnal rhythm that is opposite from the diurnal rhythm of cholesterol synthesis ( 59 ) . / stanols and in particular single dose of plant sterols / stanols reduce ldl levels , and until there are more studies on consumption of plant sterols / stanols as single dose ; plant sterols should be consumed in two to three portions per day . in conclusion , plant sterol / stanol containing products significantly reduced ldl concentrations but the reduction was related to individuals baseline ldl levels , food carrier , frequency and time of intake . the contribution of the authors were as follow : ssa designed and implemented the search strategy , assessed study quality , extracted data , performed statistical analysis , interpreted the results and wrote and edited the manuscript . rib was involved in literature search , study selection and quality assessment , and data extraction . we would like to thank mrs mary cheang , a statistical consultant at the department of community health sciences , university of manitoba , for reviewing the method section and providing statistical advice . pjhj is a consultant for danone , unilever , forbes meditech , whitewave and enymotec inc . for parallel trials , endpoint ldl cholesterol in the treatment group was subtracted from endpoint ldl cholesterol in the control group ( 46 ) . for crossover trials , ldl cholesterol values at the end of the treatment period were subtracted from ldl cholesterol values at the end of the control period ( 46 ) . within - individual changes the estimates of es are :  for parallel trials : esii = tf  cf 
  esii = the effect size of a parallel design trial , tf = final ldl cholesterol mean in the treatment group cf = final ldl cholesterol mean in the control group  for crossover trials : esx = t  c esx = the effect size of a crossover design trial t  =  ldl cholesterol mean at the end of the treatment period c  =  ldl cholesterol mean at the end of the control period for parallel trials : the se of es for a parallel study was calculated as follows 
					 seii=(sdt)2/nt+(sdc)2/nc 
				 where seii = standard error of effect size for a parallel study sdt = standard deviation of ldl - cholesterol endpoints in the treatment group sdc = standard deviation of ldl - cholesterol endpoints in the control nt = sample size of the treatment group nc = sample size of the control group sds were extracted from the studies or , if not reported , derived from se of mean or ci for group mean , ( 46 ) as follows : standard error of group mean  =  sd/n  from ci for group mean : sd  =  n x ( upper limit - lower limit)/2 * t ( 1-confidence 
 level , 
 degree 
 of 
 freedom ) 
  t ( 1-confidence 
 level , 
 degree 
 of 
 freedom ) is the t - value associate with study confidence level , usually 95% , and sample size of group  for crossover trials ( 46 , 86 ) : the se of es for a crossover study was calculated as follows sex = standard error of effect size for a crossover study sd(diff)=standard deviation of difference between the treatment period and the control period sex was extracted from reported statistical values in the trial , paired t - value or p - value , ci from a paired analysis or imputed from a number of studies as follows : diff is mean of difference between control period and treatment period if only the exact p - value or the upper bounded p - value of the paired t - test was reported , then the correspondent t - value for that p - value was calculated by entering the p - value and the degree of freedom into a spreadsheet as follows:=tinv(p - value , 
 degree 
 of 
 freedom ) 
  sex=(upper limit  lower limit)/2 * t ( 1-confidence 
 level , 
 degree 
 of 
 freedom ) 
  t ( 1-confidence 
 level , 
 degree 
 of 
 freedom ) is the t - value associate with study confidence level , usually 95% , and degree of freedom  from imputed sd(diff ) : 

 imputed  sd(diff)=(sd2+sd2-(2rsdtsdc ) ) 
				 where sd(diff)=standard deviation of difference between the treatment period and the control period 
 sdt2 
						 = ldl - cholesterol variance at the end of the treatment period 
 sdc2 
						 = ldl - cholesterol variance at the end of the control period 
 r=0.81 which is within - individual correlation between the treatment and control periods that was calculated from a number of studies . treatment es and its se were calculated for every trial as described above . to obtain the pooled treatment es , the es estimates and se were entered into revman 4.2 under the  generic inverse variance  outcome . in the inverse variance method the weight given to each study is chosen to be the inverse of the variance of the effect estimate . a fixed effect meta - analysis using the inverse variance method calculates a weighted average as follows : 
 generic inverse variance weighted average=(esi / sei2)(1/sei2 ) 
 
 es 
 i is the effect size in study i , se 
 i is the standard error of that estimate and the summation is across all studies . calculation of within - individual correlation between the treatment and control periods for crossover studies 
 sd ( mmol / l)study idcontroltreatmentdifferencerabumweis 2006a ( 32)0.931.010.510.87abumweis 2006b ( 32)0.931.060.590.83noakes 2005a ( 16)0.740.710.320.91noakes 2005b ( 16)0.740.760.320.91jones 2003a ( 27)0.891.080.640.81jones 2003b ( 27)0.890.810.510.83judd 2002 ( 70)0.280.280.280.50jones 2000a ( 50)0.700.590.400.82jones 2000b ( 50)0.700.740.390.86average  =  0.81 
 where 
 r = within - individual correlation between the treatment and control periods and was calculated as follows : 
					 r=(control sd)2+(treatment sd)2-(difference sd)22(control sd)(treatment sd )
backgroundconsumption of plant sterols has been reported to reduce low density lipoprotein ( ldl ) cholesterol concentrations by 515% . 
 factors that affect plant sterol efficacy are still to be determined.objectivesto more precisely quantify the effect of plant sterol enriched products on ldl cholesterol concentrations than what is reported previously , and to identify and quantify the effects of subjects characteristics , food carrier , frequency and time of intake on efficacy of plant sterols as cholesterol lowering agents.designfifty-nine eligible randomized clinical trials published from 1992 to 2006 were identified from five databases . weighted 
 mean effect sizes were calculated for net differences in ldl levels using a random effect model.resultsplant sterol containing products decreased ldl levels by 0.31 mmol / l ( 95% ci , 0.35 to 0.27 , p=  <  0.0001 ) compared with placebo . between trial heterogeneity 
 was evident ( chi - square test , p  =  < 0.0001 ) indicating that the observed differences between trial results were unlikely to have been caused by chance . 
 reductions in ldl levels were greater in individuals with high baseline ldl levels compared with those with normal to borderline baseline ldl levels . 
 reductions in ldl were greater when plant sterols were incorporated into fat spreads , mayonnaise and salad dressing , milk and yoghurt comparing with other food products such as croissants and muffins , orange juice , non - fat beverages , cereal bars , and chocolate . 
 plant sterols consumed as a single morning dose did not have a significant effect on ldl cholesterol levels.conclusionplant sterol containing products reduced ldl concentrations but the reduction was related to individuals baseline ldl levels , food carrier , and frequency and time of intake .