bariatric surgery ( bibp and agb ) is routinely performed at the obesity centers of the institutions participating in this study .
patients are eligible for bariatric surgery if they meet the following criteria : 1865 years of age and a bmi > 40.0 kg / m alone or a bmi > 35.0
kg / m in the presence of comorbidities , plus a history of at least two previous dietary attempts followed by a relapse .
the clinical protocol includes a medical history , physical and biochemical evaluation , and a psychological and psychiatric evaluation performed to verify indications , contraindications , and safety of surgical procedures ( 3,8 ) .
for all subjects undergoing bibp or agb , after surgery the suggested diet is 970 and 1,090 kcal per day in women and men , respectively ; iron is supplemented on the basis of blood examinations performed during the 2nd month .
the diet includes 48% carbohydrates ( starch or bread ) , 33% proteins ( fat - free parts of different animals and fishes ) , and 19% lipids ( olive oil ) ; sweets , cakes , sweetened drinks , alcohol , and animal lipids are forbidden .
all foods have to be cooked without oil , butter , or other lipids ; in addition , bibp patients receive vitamin d3 at discharge ( two administrations per month ) , vitamin b12 ( 5,000 units once per month ) , and oral antidiarrheal drugs ( diphenoxylate or loperamide ) when there are > 10 bowel movements per day ( 3,8 ) .
this was a nonrandomized , self - selected , unblinded , active - comparator , bicenter , 6-month study .
the subjects , all caucasian , were informed about the nature and aims of the cholesterol metabolism evaluation protocol , and they signed a written informed consent .
the choice of surgical procedure was made by the patient together with the surgeon , after a full explanation of the risks and possible benefits of each procedure . in total , 10 subjects underwent bibp and 10 underwent agb .
after all interventions , subjects were re - evaluated by a dietitian and physician at 2-week intervals for 2 months and then monthly for up to 6 months , as previously described ( 3,8 ) . at baseline and 6
months after surgical procedures , the subjects were studied in the early morning in a recumbent position and after an overnight fast .
height and weight were measured to the nearest 0.5 cm and 0.1 kg , respectively .
a venous line was used for blood sampling , and another venous line on the opposite arm was used for infusions .
both venous lines were kept patent by a slow 0.9% nacl saline drip . after a blood drawing for metabolites , sequential infusions of deuterated oxysterols
were performed between 9:00 a.m. and 2:00 p.m. , according to a previously published protocol ( 9 ) .
serum samples were obtained from blood collected during the sequential infusions of the two hydroxysterols at 0 , 60 , 80 , 100 , and 120 min .
plant sterols ( campesterol and sitosterol ) were measured as biomarkers of cholesterol absorption , and lathosterol as a marker of cholesterol synthesis ( 10 ) .
7--oh - cholesterol and 27-oh - cholesterol are markers of bile acid metabolism , the former of direct intrahepatic metabolism and the latter of mainly extrahepatic catabolism ( 9 ) ; bile acid synthesis accounts for > 95% of cholesterol catabolism per day ( 9 ) .
plasma glucose was measured by the glucose oxidation method ( ysi , inc . , yellow springs , oh ) .
serum insulin was assayed by microparticle enzyme immunoassay ( abbott laboratories , pasadena , ca ) ( 8) .
total cholesterol , hdl cholesterol , and triglyceride levels were assayed by automated enzymatic methods ( roche , basel , switzerland ) .
non - hdl cholesterol was calculated as total cholesterol  hdl cholesterol ( 12 ) .
the homeostasis model assessment of insulin resistance [ homa - ir ] index was calculated as blood glucose ( mmol / l )  insulin ( u / ml )  22.5 ( 13 ) .
quantitative evaluation of lathosterol , campesterol , and -sitosterol in serum was performed by a gas - liquid chromatography / mass spectrometry ( gc / ms)based technique as previously described ( 14 ) . for determination of hydroxysterol
serum concentrations , after the addition of 250 ng 19-oh - cholesterol as internal standard to 0.2 ml serum , samples were hydrolyzed and extracted ( 15 ) . the organic phase was evaporated to dryness under a stream of nitrogen and purified by solid - phase extraction .
the fraction containing the hydroxysterols was dried and treated with trimethylsilylimidazole : piperidine ( 1:1 ) before analysis by gc / ms . deuterated ( d6 )
7--oh - cholesterol was obtained by chemical synthesis from deuterated ( d6 ) cholesterol , according to previously described methods ( 15 ) , and deuterated 27-oh - cholesterol was prepared by synthesis from kryptogenin , using the clemmensen reduction method , as previously described ( 16 ) .
homogeneous suspensions of the sterols in 5% human albumin were prepared on the same day of the infusion experiment ( final concentration of 3 and 6 mg / ml of deuterated 7-- and 27-oh - cholesterol , respectively ) and filtered through a 0.22-m millipore membrane immediately before infusion , under a laminar flow hood ( 14 ) .
serum samples , obtained from blood collected during the sequential infusions of the two hydroxysterols ( see above ) , were analyzed for deuterium enrichment of 7-- and 27-oh - cholesterol using gc / ms on extracted oxysterols as previously reported ( 14 ) .
the in vivo rate of appearance of the two hydroxysterols was calculated as milligrams per hour from the deuterated / natural sterol ion ratio and infusion rate using the equation described for the steady state by duane and javitt ( 17 ) .
intergroup comparisons and within - group differences were performed by student t test for unpaired and paired data , respectively ; changes before and after 6 months between the two surgical procedures were also compared by student t test for unpaired data .
p < 0.05 was considered statistically significant . the sample size allowed for the detection of a 50% difference or more between subjects undergoing restrictive or malabsorptive procedures in total cholesterol decrease , with a type 1 error of 0.05 and a power of 0.8 .
assuming a difference in cholesterol decrease of 50 mg / dl with an sd of 10 mg / dl ( 2,57 ) , and a rate of 1:1 between the two groups of subjects , 16 subjects were required . assuming 15% would be noncompleters , 20 subjects were included .
this was a nonrandomized , self - selected , unblinded , active - comparator , bicenter , 6-month study .
the subjects , all caucasian , were informed about the nature and aims of the cholesterol metabolism evaluation protocol , and they signed a written informed consent .
the choice of surgical procedure was made by the patient together with the surgeon , after a full explanation of the risks and possible benefits of each procedure . in total , 10 subjects underwent bibp and 10 underwent agb .
after all interventions , subjects were re - evaluated by a dietitian and physician at 2-week intervals for 2 months and then monthly for up to 6 months , as previously described ( 3,8 ) . at baseline and 6
months after surgical procedures , the subjects were studied in the early morning in a recumbent position and after an overnight fast .
height and weight were measured to the nearest 0.5 cm and 0.1 kg , respectively .
a venous line was used for blood sampling , and another venous line on the opposite arm was used for infusions . both venous lines were kept patent by a slow 0.9% nacl saline drip . after a blood drawing for metabolites , sequential infusions of deuterated oxysterols were performed between 9:00 a.m. and 2:00 p.m. , according to a previously published protocol ( 9 ) .
serum samples were obtained from blood collected during the sequential infusions of the two hydroxysterols at 0 , 60 , 80 , 100 , and 120 min .
plant sterols ( campesterol and sitosterol ) were measured as biomarkers of cholesterol absorption , and lathosterol as a marker of cholesterol synthesis ( 10 ) .
7--oh - cholesterol and 27-oh - cholesterol are markers of bile acid metabolism , the former of direct intrahepatic metabolism and the latter of mainly extrahepatic catabolism ( 9 ) ; bile acid synthesis accounts for > 95% of cholesterol catabolism per day ( 9 ) .
plasma glucose was measured by the glucose oxidation method ( ysi , inc . , yellow springs , oh ) .
serum insulin was assayed by microparticle enzyme immunoassay ( abbott laboratories , pasadena , ca ) ( 8) .
total cholesterol , hdl cholesterol , and triglyceride levels were assayed by automated enzymatic methods ( roche , basel , switzerland ) .
non - hdl cholesterol was calculated as total cholesterol  hdl cholesterol ( 12 ) .
the homeostasis model assessment of insulin resistance [ homa - ir ] index was calculated as blood glucose ( mmol / l )  insulin ( u / ml )  22.5 ( 13 ) .
quantitative evaluation of lathosterol , campesterol , and -sitosterol in serum was performed by a gas - liquid chromatography / mass spectrometry ( gc / ms)based technique as previously described ( 14 ) . for determination of hydroxysterol
serum concentrations , after the addition of 250 ng 19-oh - cholesterol as internal standard to 0.2 ml serum , samples were hydrolyzed and extracted ( 15 ) . the organic phase was evaporated to dryness under a stream of nitrogen and purified by solid - phase extraction .
the fraction containing the hydroxysterols was dried and treated with trimethylsilylimidazole : piperidine ( 1:1 ) before analysis by gc / ms .
deuterated ( d6 ) 7--oh - cholesterol was obtained by chemical synthesis from deuterated ( d6 ) cholesterol , according to previously described methods ( 15 ) , and deuterated 27-oh - cholesterol was prepared by synthesis from kryptogenin , using the clemmensen reduction method , as previously described ( 16 ) .
homogeneous suspensions of the sterols in 5% human albumin were prepared on the same day of the infusion experiment ( final concentration of 3 and 6 mg / ml of deuterated 7-- and 27-oh - cholesterol , respectively ) and filtered through a 0.22-m millipore membrane immediately before infusion , under a laminar flow hood ( 14 ) .
serum samples , obtained from blood collected during the sequential infusions of the two hydroxysterols ( see above ) , were analyzed for deuterium enrichment of 7-- and 27-oh - cholesterol using gc / ms on extracted oxysterols as previously reported ( 14 ) .
the in vivo rate of appearance of the two hydroxysterols was calculated as milligrams per hour from the deuterated / natural sterol ion ratio and infusion rate using the equation described for the steady state by duane and javitt ( 17 ) .
intergroup comparisons and within - group differences were performed by student t test for unpaired and paired data , respectively ; changes before and after 6 months between the two surgical procedures were also compared by student t test for unpaired data .
the sample size allowed for the detection of a 50% difference or more between subjects undergoing restrictive or malabsorptive procedures in total cholesterol decrease , with a type 1 error of 0.05 and a power of 0.8 . assuming a difference in cholesterol decrease of 50 mg / dl with an sd of 10 mg / dl ( 2,57 ) , and a rate of 1:1 between the two groups of subjects , 16 subjects were required . assuming 15% would be noncompleters ,
table 1 shows the clinical and metabolic data of obese subjects entering the study ; all variables were similar in the two groups , with no significant difference . clinical and metabolic details of obese subjects in the study , divided by surgical technique figure 1 shows that the decrease of bmi , homa - ir , and triglycerides was similar in the two groups ; a small but significant decrease was observed in hdl cholesterol levels in subjects undergoing bibp , but with no significant difference from subjects undergoing agb . also , blood glucose and insulin levels decreased in a significant manner , with no difference between bibp and agb ( not shown ) .
in contrast , total cholesterol and ldl cholesterol levels were affected in a different way by bibp and agb , with a clear intergroup difference .
p values between columns ( two - sided arrows ) indicate significance of intergroup differences .
figure 2 shows that non - hdl cholesterol , sitosterol , and campesterol levels decreased with bibp , but not with agb .
serum lathosterol increased with bibp , but not with agb , with a significant difference between bibp and agb .
changes of non - hdl cholesterol and of biomarkers of intestinal absorption of cholesterol ( sitosterol and campesterol ) and of cholesterol synthesis ( lathosterol ) induced by bibp and agb . baseline ( black columns ) and postsurgery ( white columns ) values are indicated .
p values between columns ( two - sided arrows ) indicate significance of intergroup differences .
figure 3 shows that the rate of appearance and serum levels of 7--oh - cholesterol increased with bibp , but not with agb , with a significant difference between bibp and agb .
the rate of appearance of 27-oh - cholesterol did not vary with either bibp or agb , but the trend was significantly different ; the serum levels of 27-oh - cholesterol decreased in a similar way with bibp and agb .
rate of appearance ( mg / h ) and serum levels ( g / dl ) of markers of bile acid metabolism before and after bibp and agb .
p values between columns ( two - sided arrows ) indicate significance of intergroup differences .
the aim of this study was to assess intestinal cholesterol absorption , cholesterol synthesis , and cholesterol catabolism in obese subjects undergoing two different surgical techniques , one based on pure malabsorption ( bibp ) and the other on restriction of the stomach ( agb ) .
the studies were performed under basal conditions and 6 months later , when the decrease of bmi was expected to be similar . although the decrease of blood glucose , insulin , homa - ir index , and triglycerides was similar between the two groups , significant differences between pre- and postsurgery cholesterol metabolism appeared in subjects undergoing bibp , but not in subjects undergoing agb . in particular , total cholesterol , ldl cholesterol , non - hdl cholesterol , campesterol , and sitosterol decreased , and lathosterol increased , together with the hepatic cholesterol catabolism pathway ( 7--oh - cholesterol ) .
this leads us to speculate that with malabsorptive surgery , cholesterol absorption decreases , which is associated with a clear decrease of ldl cholesterol ( and of non - hdl cholesterol ) . as a compensation , cholesterol synthesis increases , and
the increase in lathosterol , a marker of cholesterol synthesis , would also point to enhanced ldl receptor activity in the liver , which would lead to reduced circulating ldl levels .
in contrast , cholesterol absorption is unchanged in restrictive surgery , and ldl cholesterol shows a small but significant increase , if any .
the only effect of purely restrictive surgery is a decrease in extrahepatic cholesterol catabolism , parallel with an increase in ldl cholesterol , a finding that at present is unexplained .
these data , obtained at 6 months , can not be assumed as representative of the full picture of cholesterol metabolism afterward ; in any case , these data indicate that different technical surgical techniques have a different effect on cholesterol levels , independent of weight loss .
diet after surgery does not seem to be of importance , as differences between bibp and agb were negligible for the fat / cholesterol content ; in addition , fat and cholesterol do not affect intestinal absorption of cholesterol as measured through plant sterols ( 10 ) .
however , it is noticeable that the different effects of bibp and agb persist for up to 3 or 6 years ( 2,57,18 ) .
the cholesterol reduction that we and others have reported after bibp , bpd , or rygb is quite a dramatic phenomenon and is likely due to the major reduction in cholesterol and bile acid reabsorption in the intestine , and possibly due to altered regulation of the feedback mechanisms controlled by nuclear proteins such as lxr , fxr , and peroxisome proliferator  activated receptor ; these transcriptional factors are involved in bile acid and cholesterol metabolism in patients undergoing bibp , bpd , or rygb ( which cause malabsorption and also reduce bile reabsorption ) but not agb ( a purely restrictive bariatric procedure ) ( 19 ) .
it is also possible that reduced gastric volume and reduced production of gastric lipase , as well as reduced secretion of cholecystokinin ( which physiologically stimulates digestive enzyme secretion such as lipases and proteases ) , might result in a marked decrease in the hydrolysis of triacylglycerols , with a reduction of the absorption of free fatty acids ( 20 ) .
bpd and rygb include partial gastric resection , or functional gastric disconnection ; therefore , gastric bypass and bpd can not be regarded as purely restrictive or purely malabsorptive surgical techniques .
blood glucose and serum insulin levels decreased to a similar extent with the two techniques , as was the case for the homa - ir index .
these data indicate that changes of cholesterol absorption , synthesis , and catabolism were independent of glycemic control , insulin , and insulin resistance . in conclusion , compared with agb , bibp provides greater cholesterol lowering .
 objectivemalabsorptive bariatric surgery ( biliopancreatic diversion and biliointestinal bypass [ bibp ] ) reduces serum cholesterol levels more than restrictive surgery ( adjustable gastric banding [ agb ] ) , and this is thought to be due to greater weight loss . 
 our aim was to evaluate the changes of cholesterol metabolism induced by malabsorptive and restrictive surgery independent of weight loss.research design and methodsin a nonrandomized , self - selected , unblinded , active - comparator , bicenter , 6-month study , glucose metabolism ( blood glucose and serum insulin levels and homeostasis model assessment of insulin resistance [ homa - ir ] index ) and cholesterol metabolism ( absorption : serum campesterol and sitosterol levels ; synthesis : serum lathosterol levels ; catabolism : rate of appearance and serum concentrations of serum 7-- and serum 27-oh - cholesterol after infusions of deuterated 7-- and 27-oh - cholesterol in sequence ) were assessed in grade 3 obesity subjects undergoing bibp ( n = 10 ) and agb ( n = 10 ) . 
 evaluations were performed before and 6 months after surgery.resultssubjects had similar values at baseline . 
 weight loss was similar in the two groups of subjects , and blood glucose , insulin levels , homa - ir , and triglycerides decreased in a similar way . 
 in contrast , serum cholesterol , ldl cholesterol , non - hdl cholesterol , serum sitosterol , and campesterol levels decreased and lathosterol levels increased only in bibp subjects , not in agb subjects . 
 a significant increase in 7--oh - cholesterol occurred only with bibp ; serum 27-oh - cholesterol decreased in both groups.conclusionsmalabsorptive surgery specifically affects cholesterol levels , independent of weight loss and independent of glucose metabolism and insulin resistance . decreased sterol absorption leads to decreased cholesterol and ldl cholesterol levels , accompanied by enhanced cholesterol synthesis and enhanced cholesterol catabolism . compared with agb , bibp provides greater cholesterol lowering . 
RESEARCH DESIGN AND METHODS
Study protocol
Blood drawing and isotope infusion
Laboratory assays
Deuterated oxysterol infusions
Statistical analysis
Sample size and power calculation
RESULTS
CONCLUSIONS