Steatorrhea and Hyperoxaluria Occur after Gastric Bypass Surgery in Obese Rats Regardless of Dietary Fat or Oxalate

Abstract

Purpose To determine the effect of dietary fat and oxalate on fecal fat excretion and urine parameters in a rat model of Roux-en-Y gastric bypass (RYGB) surgery. Materials and Methods Diet-induced obese Sprague Dawley rats underwent sham (Control, n=16) or RYGB (n=19) surgery. Once recovered, animals were fed ad lib normal calcium, high fat (40%) diet with (Ox) or without (No Ox) 1.5% potassium oxalate for 5 weeks, then normal (10%) fat diet for 2 weeks. Stool and urine were collected after each period. Fecal fat was determined by gas chromatography and urine metabolites by assay spectrophotometry. Results Daily fecal fat excretion remained low in controls on either diet. RYGB animals, however, ingested similar food quantity as controls yet had 8-fold higher fecal fat excretion (p<0.001) and heavier stools (p=0.02). On high fat, RYGB Ox had 5-fold increase in urine oxalate excretion (p<0.001) while RYGB No Ox had 2-fold increase in urine calcium (p<0.01) versus controls. Lowering dietary fat in RYGB Ox animals led to a 50% decrease in oxalate excretion (p<0.01), a 30% reduction in urinary calcium, and an increase in urine pH by 0.3 units (p<0.001). Conclusions In this RYGB model, high fat feeding resulted in steatorrhea, hyperoxaluria, and low urine pH, partially reversible by lowering dietary fat and oxalate content. RYGB animals on normal fat and no oxalate diets excreted twice as much oxalate as age-matched, sham controls. Although RYGB-hyperoxaluria appears primarily gut and diet-mediated, secondary causes of oxalogenesis from liver or other mechanisms deserve further exploration.

The physiology underlying Roux-en-Y gastric bypass: a status report

“…In rats operated in our own laboratory, temporary malabsorption was also occasionally observed under conditions of high-fat feeding (e.g., 60% fat by calories), but the contribution to body weight loss seemed to be minor. A recent study by Canales et al (21) also indicated that fat malabsorption may be a direct consequence of RYGB surgery (21). In that study, it was, however, surprising that the relative fat absorption appeared to be higher when the rats were fed a 40% fat diet compared with a 10% fat diet; given that a limited capacity to absorb dietary fat in RYGB rats may have led to a ceiling effect for absolute fat transport capacity, we would have expected rather the opposite when fat absorption was expressed as percent absorption.…”

“…Under conditions of high-fat feeding, macronutrient maldigestion and malabsorption may, at least in part, contribute to the negative energy balance of RYGB compared with shamoperated rats (21,143); in other words, caloric malabsorption may contribute to the RYGB-induced body weight loss if animals are maintained on a high-fat diet (21, 132, 143). In rats operated in our own laboratory, temporary malabsorption was also occasionally observed under conditions of high-fat feeding (e.g., 60% fat by calories), but the contribution to body weight loss seemed to be minor.…”

Animal models of urinary stone disease

“…This study examined stool and urine for respective fecal fat content and [20] Free drinking of water with powdered 3% glycolic acid Hyperoxaluria Hypocitraturia CaOx crystal deposits Ethylene Glycol (EG) [16,21e29] 0 This study also found that all RYGB rats had a 250% increase in water consumption and a 2-fold increase in urine volume excretion, regardless of dietary oxalate or fat content. While postulated to be due to altered thirst mechanisms [46], it highlights a major difference compared to results from previous human studies that have shown significant decreases in urine volume post-RYGB [44,47,48]. Future studies are needed to further elucidate the impact of RYGB and urinary volume production.…”

“…Canales et al investigated the mechanism by which post-RYGB hyperoxaluria takes place by utilizing a diet induced obesity (DIO) model in male Sprague-Dawley rats followed by randomized intervention to either sham surgery (controls) or RYGB [46]. This study examined stool and urine for respective fecal fat content and [20] Free drinking of water with powdered 3% glycolic acid Hyperoxaluria Hypocitraturia CaOx crystal deposits Ethylene Glycol (EG) [16,21e29] 0 This study also found that all RYGB rats had a 250% increase in water consumption and a 2-fold increase in urine volume excretion, regardless of dietary oxalate or fat content.…”

Kidney Stones After Bariatric Surgery: Risk Assessment and Mitigation

“…Several groups have found experimental RYGB surgery to be associated with a development of a metabolic acidosis in rodents. 38,39 Likewise, the literature reports that citrate salts, such as potassium citrate, and alkali are able to play a role correcting hypocitraturia and metabolic acidosis. 15,28,32,40 Randomized controlled trials have demonstrated that potassium citrate is FIG.…”