Use of barium sulphate as a continuous marker for faeces

Steatorrhea and Hyperoxaluria in Severely Obese Patients Before and After Roux-en-Y Gastric Bypass

BACKGROUND AND AIMS

Hyperoxaluria after Roux-en-Y gastric bypass (RYGB) is generally attributed to fat malabsorption. If hyperoxaluria is indeed caused by fat malabsorption, magnitudes of hyperoxaluria and steatorrhea should correlate. Severely obese patients, prior to bypass, ingest excess dietary fat that can produce hyperphagic steatorrhea. The primary objective of the study was to determine whether urine oxalate excretion correlates with elements of fat balance in severely obese patients before and after RYGB.

METHODS

Fat balance and urine oxalate excretion were measured simultaneously in 26 severely obese patients before and 1 year after RYGB, while patients consumed their usual diet. At these time points, stool and urine samples were collected. Steatorrhea and hyperoxaluria were defined as fecal fat >7 g/day and urine oxalate >40 mg/day. Differences were evaluated using paired 2-tailed t tests.

RESULTS

Prior to RYGB, 12 of 26 patients had mild to moderate steatorrhea. Average urine oxalate excretion was 61 mg/day; there was no correlation between fecal fat and urine oxalate excretion. After RYGB, 24 of 26 patients had steatorrhea and urine oxalate excretion averaged 69 mg/day, with a positive correlation between fecal fat and urine oxalate excretions (r = 0.71, P < .001). For each 10 g/day increase in fecal fat output, fecal water excretion increased only 46 mL/day.

CONCLUSIONS

Steatorrhea and hyperoxaluria were common in obese patients before bypass, but hyperoxaluria was not caused by excess unabsorbed fatty acids. Hyperphagia, obesity, or metabolic syndrome could have produced this previously unrecognized hyperoxaluric state by stimulating absorption or endogenous synthesis of oxalate. Hyperoxaluria after RYGB correlated with steatorrhea and was presumably caused by excess fatty acids in the intestinal lumen. Because post-bypass steatorrhea caused little increase in fecal water excretion, most patients with steatorrhea did not consider themselves to have diarrhea. Before and after RYGB, high oxalate intake contributed to the severity of hyperoxaluria.

The contribution of malabsorption to the reduction in net energy absorption after long-limb Roux-en-Y gastric bypass

BACKGROUND

Roux-en-Y gastric bypass (RYGB) restricts food intake, and when the Roux limb is elongated to 150 cm, the procedure is believed to induce malabsorption.

OBJECTIVE

Our objective was to measure total reduction in intestinal absorption of combustible energy after RYGB and the extent to which this was due to restriction of food intake or malabsorption of ingested macronutrients.

DESIGN

Long-limb RYGB was performed in 9 severely obese patients. Dietary intake and intestinal absorption of fat, protein, carbohydrate, and combustible energy were measured before and at 2 intervals after bypass. By using coefficients of absorption to measure absorptive function, equations were developed to calculate the daily gram and kilocalorie quantities of ingested macronutrients that were not absorbed because of malabsorption or restricted food intake.

RESULTS

Coefficients of fat absorption were 92 ± 1.3% before bypass, 72 ± 5.5% 5 mo after bypass, and 68 ± 8.7% 14 mo after bypass. There were no statistically significant effects of RYGB on protein or carbohydrate absorption coefficients, although protein coefficients decreased substantially in some patients. Five months after bypass, malabsorption reduced absorption of combustible energy by 124 ± 57 kcal/d, whereas restriction of food intake reduced energy absorption by 2062 ± 271 kcal/d. Fourteen months after bypass, malabsorption reduced energy absorption by 172 ± 60 kcal/d compared with 1418 ± 171 kcal/d caused by restricted food intake.

CONCLUSION

On average, malabsorption accounted for ≈6% and 11% of the total reduction in combustible energy absorption at 5 and 14 mo, respectively, after this gastric bypass procedure.

Assessment of fat malabsorption

For the assessment of fat malabsorption, the standard method of measuring faecal fat excretion using a 5 day stool collection has been compared with the alternative methods: stool microscopy, a lipid tolerance test and a continuous marker technique for the estimation of fat content on a single stool sample. The lipid test, using an emulsion of arachis oil (Prosparol), was less reliable than had been expected with a sensitivity of 33% and a specificity of 45.4%. Stool microscopy using Oil Red O to stain fat globules had a sensitivity of 72.2% and a specificity of 95.4%. Fat estimation of a single stool sample using copper (1) thiocyanate showed a high correlation with that determined on a 5 day stool collection (p less than 0.001). It is concluded that lipid tolerance tests have little place in the estimation of fat absorption. In laboratories where faecal fats are not measured, microscopic examination of stool for fat globules provides a specific and relatively sensitive method for detecting steatorrhoea. The use of a continuous marker provides a method for assessing the degree of steatorrhoea on a single stool sample without the disadvantages of the conventional method of faecal fat analysis.

A simple and reliable method for calcium balance using combined period and continuous fecal markers

Calcium balances were determined in 13 patients during 2--4 3-day periods following both period marking (with carmine) and continuous marking (with polyethylene glycol or chromium). The reliability coefficient for the uncorrected fecal calcium (obtained from period marking) from one period to another was 0.82, whereas it was 0.97 for corrected fecal calcium (determined from recovery of continuous marker in 3-day fecal pools). Thus, the addition of continuous marking yielded a significantly more reliable measure of fecal calcium than obtainable by the use of period marking alone (p < 0.05); the error variance for corrected fecal calcium from one period to another was 3%, whereas it was 18% for uncorrected fecal calcium. It is concluded that a reliable measure of fecal calcium, and hence calcium balance, could be obtained by combined use of continuous and period markers, involving fecal collection over only one 3-day study period (marked by period marker), and correction of fecal calcium for the completeness of fecal collection (determined from continuous fecal marker).

Radio-opaque pellets as faecal markers for faecal fat estimation in malabsorption

Thirty-seven patients undergoing routine investigation for malabsorption were given radio-opaque pellets (ROP) which were compared with polyethylene glycol and chromic oxide as continuous faecal markers. Percentage recovery of all markers showed a wide range. The recovery of all markers was very similar, and radio-opaque pellet-corrected daily faecal fat correlated very closely with PEG-and chromic oxide-corrected fat results. Estimation of ROP is precise, simple, and minimises faecal handling. ROP are suitable for routine use in faecal fat studies and have advantages over markers used at present.

Comparison of radio-opaque pellets and chromium sesquioxide as inert markers in studies requiring accurate faecal collections

Radio-opaque pellets (ROP) similar to those currently used to measure gastrointestinal transit time have been compared with chromium sesquioxide to assess their suitability for use as inert markers in the gut. Five healthy subjects took both markers with every meal for two separate three week periods while taking metabolically controlled diets. Overall recovery of both markers was satisfactory; ROP 99.7 +/- 0.3% (SD) and chromium 97.8 +/- 1.6% (SD). A comparison of the amount for each marker recovered in 69 separate faecal collection periods of various lengths showed close agreement (R = 0.99) and the tail-off in marker excretion after cessation of ROP and chromium intake was similar, although slightly more prolonged for chromium. The amount of marker retained in the gut was 13.5% greater for chromium at the end of the three week study periods. Both markers proved satisfactory for correcting variations in faecal calcium output. The ROP, however, offer clear advantages over chromium in that they are considerably easier and quicker to measure, the method of measurement using x-rays does not alter the stools and faecal handling is minimised. The precision of ROP measurement is greater and, because of the variety of ROP available, they offer more flexibility for metabolic studies. In addition, stool by stool analysis is possible enabling simultaneous measurement of mean transit time to be made in experimental subjects.

The metabolic balance technique: a critical reappraisal

Twenty-six metabolic balance studies (MBS) of Ca, Mg, and P have been conducted in 11 postmenopausal women with osteoporosis and in 4 patients suffering from Paget's disease of bone. Subjects were given a liquid formula diet (LFD) matched as closely as possible to the patient's home diet. Studies lasted for 25 days, separated into 5-day periods by a carmine marker combines with Cr2O3 as continuous fecal marker. The balance studies were combined with a tracer technique using 47Ca to detect a possible loss of Ca by perspiration. The reliability of analytical methods necessary for mineral balances was tested. In 22 of the 26 MBS a steady state (SS) reflecting the patient's regular living conditions was demonstrated, while a non-SS situation possibly due to changes of physical activity was seen in four instances. The overall precision and accuracy of this balance method for Ca and P was found to be better than plus or minus 50 mg/day after four periods and plus or minus 40 mg/day after five periods, as related to an average daily intake of 920 mg Ca and 1230 mg P. For Mg (intake 190 mg/day), a precision of plus or minus 10 mg/day was recorded. The dermal loss of Ca was found to be less than 20 mg/day. As shown for Ca, Mg and P, the precision of a balance study is only little enhanced when the investigation is continued for more than four periods. At the present time is not possible to predict non-SS situations before starting such a study but a simple formula is proposed to detect those which were not performed under SS conditions.

Polyethylene glycol 4000 as a continuously administered non-absorbable faecal marker for metabolic balance studies in human subjects

The use of polyethylene glycol 4000 as a non-absorbable, continuously fed faecal marker is described. The intestinal handling and transit of polyethylene glycol is compared with that of chromium sesquioxide and barium sulphate. Polyethylene glycol is an acceptable non-absorbable faecal marker for calcium, phosphorus, and fatty acids, and has several features which commend its use in preference to insoluble chromium sesquioxide and barium sulphate particularly when marking water-soluble dietary constituents.

A ne method for studying gut transit times using radioopaque markers

A simple technique for measuring gastrointestinal transit times using radioopaque pellets of barium-impregnated polythene has been developed and validated. A normal range has been established by studying 25 normal subjects; all passed the first marker within three days and most passed 80% of the markers within five days.