Cholesterol saturation of bile after jejunoileal bypass increases more with a 1:3 than with a 3:1 jejunoileal ratio

Targeting bile acid metabolism in obesity reduction: A systematic review and meta-analysis

A systematic review and meta-analysis was conducted of studies that address the association of bile acid (BA) with obesity and of studies on the effects of treatment in patients with obesity on BA metabolism, assessed from systemic BA, fibroblast growth factor 19 (FGF19), 7α-hydroxy-4-cholesten-3-one (C4) level, and faecal BA. We searched PubMed, Embase, and the Cochrane Library from inception to 1 August 2019 using the keywords obesity, obese, body mass index, and overweight with bile acid, FGF19, FXR, and TGR5. Two reviewers independently searched, selected, and assessed the quality of studies. Data were analysed using either fixed or random effect models with inverse variance weighting. Of 3771 articles, 33 papers were relevant for the association of BA with obesity of which 22 were included in the meta-analysis, and 50 papers were relevant for the effect of obesity interventions on BA of which 20 were included in the meta-analysis. Circulating fasting total BA was not associated with obesity. FGF19 was inversely and faecal BA excretion was positively associated with obesity. Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) modulated BA metabolism, ie, increased BA and FGF19. Our results indicate that BA metabolism is altered in obesity. Certain bariatric surgeries including RYGB and SG modulate BA, whether these underlie the beneficial effect of the treatment should be investigated.

Bile acids in health and disease

Over the last quarter of a century Danish research on bile acids has comprised studies of their physical and chemical properties, their physiology, pathophysiology, metabolism, and kinetics, and their clinical applicability. In the beginning of the period a major contribution was made to the understanding of the factors involved in the solubility of cholesterol in bile. The growing international understanding of the potential importance of the bile acids in health and disease gave raise to a substantial Danish contribution in the 1970s and 1980s in parallel with international achievements. Emphasis was on the possible clinical implications of bile acids. Studies on physiology and pathophysiology were in focus. Patients who have had an intestinal bypass operation for obesity served as a model for obtaining new knowledge on various aspects of the properties of the bile acids. Also the analytical methods were improved. Important physiological research on the mechanisms of hepatic bile flow was conducted. An intestinal perfusion model served as a tool providing information on absorption kinetics and on transmucosal water and electrolyte movements. The gallstone disease, liver diseases, inflammatory bowel disease, fat malabsorption, and other intestinal disorders were studied. The 'idiopathic ileopathy' as a cause for bile acid malabsorption causing diarrhoea was established as a new disorder. Thus, in the time period concerned, substantial Danish contributions emerged on major and minor topics of the bile acid field.

Faecal steroids after jejunoileal bypass with 3:1 or 1:3 jejunoileal ratio

The faecal steroid excretion was assessed after jejunoileal bypass with a 3:1 ratio (n = 14) and with a 1:3 ratio (n = 9) between the jejunal and ileal segment left in continuity. The bile acid excretion with a 1:3 bypass was 49% of that with a 3:1 bypass (P less than 0.01), with a slight predominance of chenodeoxycholic over cholic acid in 1:3 compared with 3:1 bypass. The excretion of neutral steroids of cholesterol origin was slightly but insignificantly higher with a 1:3 bypass. Accordingly, the faecal bile acids contributed significantly less to total faecal steroids with a 1:3 bypass. The net sterol loss was higher, although not significantly so, with a 3:1 than with a 1:3 jejunoileal ratio. The study indicates that the 1:3, compared with the 3:1, jejunoileal ratio of the bypass reduces bile acid excretion considerably, whereas the effect on cholesterol turnover appears to be less pronounced.

Bile acid malabsorption after jejunoileal bypass is less compensated for with a 1:3 than with a 3:1 jejunoileal ratio

A previous study surprisingly showed that after jejunoileal bypass a ratio of 1:3 compared with 3:1 between the jejunal and ileal segment left in continuity resulted in a smaller synthesis rate, pool size, and postcibal jejunal levels of bile acids. These findings are reevaluated in the present study of 34 patients who either were waiting for or 3, 9, or 15 months earlier, had undergone bypass surgery with a 3:1 or 1:3 jejunoileal ratio. Compared with 3:1 bypass, the 1:3 bypass resulted in (i) greater reduction of the fasting bile acid pool, significant for chenodeoxycholic acid but not for cholic adic, (ii) less increase in synthesis rate of both bile acids, (iii) less decrease in relative content of taurine-conjugated bile acids in bile, and (iv) equal reduction of postcibal levels of bile acids in jejunum. We conclude that the increase in synthesis of bile acids compensates insufficiently for the excess fecal loss; the lower synthesis rate after bypass with a short jejunum relative to ileum in function may be due to an impaired stumulation of bile acid synthesis, the mechanism of which is unexplained.

Plasma cholesterol fractions after jejunoileal bypass with 3:1 or 1:3 jejunoileal ratio

Jejunoileal bypass results in a 40% reduction in total plasma cholesterol both with a 3:1 and with a 1:3 jejunoileal ratio of the segments left in continuity, in spite of a lower rate of cholesterol degradation to bile salts with a 1:3 jejunoileal ratio. We measured total cholesterol, total triglycerides, and high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol in plasma from 34 patients who either were waiting for or had had bypass surgery with 3:1 or 1:3 jejunoileal ratio 3, 9, or 15 months earlier. Total cholesterol and triglycerides were significantly reduced after bypass surgery but showed no significant difference between 3:1 and 1:3 bypass and no significant changes with time after surgery. The HDL cholesterol showed no significant differences between the groups except for a moderately decreased level in the 1:3 bypass group 3 months after surgery. LDL cholesterol was pronouncedly reduced in the bypass groups compared with the unoperated group and was not significantly related to the jejunoileal ratio of the bypass or to the time since surgery.