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SOS study

Bariatric surgery has beneficial effects on liver

Sustained weight loss has a beneficial long-term effect on chronic liver damage

Bariatric surgery has beneficial effects on liver function according to the latest paper from the Swedish Obese Subjects (SOS) study. The paper, published online in Plos One, found that surgery results in a sustained reduction in transaminase levels, and a long-term benefit in obese individuals.

“These data indicate that sustained weight loss has a beneficial long-term effect on chronic liver damage and that this effect is proportional to the weight loss reduction,” the authors write.

A transaminase is a type of enzyme whose activity is frequently measured, as part of a standard series of tests, to determine liver function. There are a number of different types of transaminases; the two commonly measured medically are alanine transaminase (ALT) and aspartate transaminase (AST). ALT is primarily localized to the liver and is considered a more specific test for liver damage.

Obesity is associated with elevated serum transaminase levels and non-alcoholic fatty liver disease and weight loss is a recommended therapeutic strategy.

As bariatric surgery is known to be effective in obtaining and maintaining weight loss, the aim of the study was to examine the long-term effects of bariatric surgery on serum transaminases in the prospective, controlled study, the SOS study.

SOS study

The SOS study is a non-randomised, matched, prospective, controlled, intervention trial that is comparing the long-term effects of bariatric surgery and usual care in obese subjects. The study includes 4,047 obese individuals of which 2,010 individuals had bariatric surgery and 2,037 individuals matched in a control group of enrolled based on 18 matching variables.

Individuals in the surgery group underwent either non-adjustable or adjustable banding (n=376), vertical banded gastroplasty (n=1,369) or gastric bypass (n=265). Subjects in the control group received the conventional treatment for obesity (advanced lifestyle modification, other or no treatment

Changes in serum transaminase levels and body weight were calculated as the difference between follow up (two or ten years) and baseline values. In addition, incidence of high transaminase during follow-up, as well as remission from high transaminase at baseline were analysed.

Specifically, the high transaminase group was defined by AST levels ≥33 U/L or 29 U/L and ALT levels ≥43 U/L or 30 U/L in men or women, respectively, as cut-offs. These transaminase cut-off levels have been shown to define NAFLD, indicated as liver fat content >5.6% by proton magnetic resonance spectroscopy in individuals with alcohol intake ≤20 (men) or ≤10 g/day (women).

Follow-up data were available for 3,102 (87%) persons after two years, and for 2,157 (60%) after ten years.

Results

A total of 3,570 individuals (control group, n=1,795; surgery group, n=1,775) from the overall SOS study population were included in the study.

Individuals in the surgery group were younger had higher body weight, BMI, blood pressure, glucose and liver transaminase levels compared to the control group. No differences in other parameters including alcohol consumption and use of lipid- and blood glucose-lowering medications were observed in the two treatment groups.

For incidence and remission calculations, the SOS individuals were stratified in groups with low (LT) and high serum transaminase (HT) levels. At baseline, the prevalence of HT levels was 46% (n=818) in the surgery group and 36% (n=645) in the control group (p<0.001).

Bariatric surgery was associated with a significant and sustained decrease in body weight compared to the control group.

After two years, both ALT and AST were reduced in the surgery group, while there was no change in the control group. After ten years, this pattern remained for ALT, while there was an increase in AST, which was significantly smaller in the surgery group than in the control group.

In addition, serum transaminase level changes were positively correlated to body weight changes at both 2- (ALT: r=0.500, p<0.001; AST: r=0.289, p<0.001) and 1- year (ALT: r 0.357, p<0.001; AST: r=0.160, p<0.001) follow up when the surgery and control groups were pooled.

The investigators report that serum AST level were related to weight loss, however, there was no further reduction in AST levels beyond weight loss of more than 10kg at 2-year follow-up. At 10-year follow up, the AST levels were associated with weight change, but compared to baseline there was no reduction in the AST levels irrespective of the weight change categories. Weight gain was associated with increased serum transaminases at both 2- and 10-year follow-up.

The incidence of HT was lower in the surgery compared to the control group at both 2-year (6% and 21%, for surgery and control groups, respectively p<0.001) and at 10-year (18% and 27%, p<0.001) follow up. A reduced risk for HT onset was observed in the surgery group at 2 and 10 years (OR: 0.26 (95% confidence interval 0.18–0.36, p<0.001) and 0.61 (95% confidence interval 0.46–0.81, p<0.001, respectively).

In addition, remission from HT was more common in the surgery group compared to the control group (80% and 39%, for surgery and control groups, respectively after 2-years, p<0.001, and 63% and 47%, respectively after 10-years, p<0.001).

Conclusion

“These data suggest that bariatric surgery has a long-term protective effect against chronic liver damage,” the authors write. “The effects after 10 years were smaller than after 2 years and this is likely due to the weight regain observed 10 years after bariatric surgery.”

They also note that the relationship between changes in transaminase levels and changes in body weight showed that weight gain was associated with a significant increase of transaminase levels, with ALT showing a continuous linear reduction with increasing weight loss at the 2-year follow up which was maintained at the 10 year follow up.

When changes in AST levels were examined, a reduction related to weight loss was observed at the 2-year but not at the 10-year follow up. The reason for this unexpected finding is unknown but it may be due to factors that have changed over time (e.g., age, environmental factors, lifestyle habits, medications) and influenced transaminase differently [23]. Nonetheless, it is worth noting that despite the absence of reduction at 10-year follow up, the AST levels remained lower in the surgery when compared to the control group.

Furthermore, the long-term effect of bariatric surgery on HT incidence and remission was examined. The incidence of and the remission from HT at both 2- and 10-year follow up were significantly more favourable in the surgery group compared to the control group. Similarly, the prevalence of an ALT/AST ratio <1, an index of severe liver disease [20], was lower in the surgery group compared to the control group at both 2- and 10-year follow up.

Although the authors acknowledge that a limitation of the report is that the effect of bariatric surgery on transaminase levels was not a predefined endpoint of the SOS study, “taken as a whole, these data suggest that weight reduction has a positive effect on liver transaminases and chronic liver damage,” they note.

“It may be speculated that sustained weight loss obtained by bariatric surgery reduces liver damage and may possibly prevent hepatic long-term sequelae,” they write. “Further longitudinal studies, using more sensitive techniques to assess chronic liver disease, are warranted to confirm these data. In conclusion, this report shows that bariatric surgery is associated with long-term reduction of serum transaminases in obese individuals.”

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