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Surgical mechanisms

Study helps to explain mechanisms of duodenal switch

Results reveal that different postsurgical effects of GB vs. DS in terms of food intake, eating rate, energy expenditure and absorption

Duodenal switch induces greater body weight loss by reducing food intake, increasing energy expenditure and causing malabsorption, compared to bypass that induces body weight loss by increasing energy expenditure, according to a study in rat models, Mechanistic Comparison between Gastric Bypass vs. Duodenal Switch with Sleeve Gastrectomy in Rat Models, published online in the journal Plos One.

The authors state that although both gastric bypass (GB) and duodenal switch have been widely used in bariatric surgeries, the latter appears to be superior to GB in terms of weight loss. The procedures have shown different efficacy in individual patients and the underlying mechanisms are not yet clear; whether this is due to biological or behavioural factors.

The aim of the study was to better understand the mechanisms leading to body weight loss by comparing these two procedures in experimental models of rats.

Study

GB was performed without the Roux-en-Y reconstruction and the postsurgical anatomy was similar to mini-GB on humans, and DS was performed according to the rat anatomy.

Thirty-four rats, at 587.0±8.1g body weight, were randomly divided into experimental (GB and DS) as well as control groups (laparotomy, LAP): GB (14 rats), DS (7 rats), and LAP (13 rats). The body weight was not different between the groups before surgery (p=0.276). Because of markedly loss of body weight after DS, the group of DS rats, together with age-matched group of laparotomized rats (LAPDS, 7 rats), were followed up only for eight weeks, while GB rats and the rest of laparotomized rats (LAPGB, 6 rats) were followed up for 14 weeks.

Outcomes

LAP alone did not reduce body weight during the study period (maximum 14 weeks). GB caused approximately 20% weight loss throughout the study period (14 weeks). DS induced approximately 50% weight loss within 8 weeks.

With regard to food intake (Figures 1 and 2), LAP and GB increased daytime (but not night-time) food intake (expressed as either kcal/rat or kcal/100 g body weight) at three weeks, and had no effects afterwards (14 weeks postoperatively). In contrast, DS reduced night-time (but not daytime) food intake (kcal/rat at both two and eight weeks or kcal/100g body weight at two weeks). The food intake (kcal/100 g) at eight weeks was not reduced because of markedly loss of the body weight after DS.

Figure 1: Total food intake (kcal/rat) (A, B) and relative food intake (kcal/100 g body weight) (C,D) during day- and night-time. Short-term after surgery: 3 weeks after gastric bypass (GB), 2 weeks after duodenal switch (DS) or 2–3 weeks after lapatoromy (LAP). Long-term after surgery: 14 weeks after GB, 8 weeks after DS or 8–14 weeks after LAP. Data are expressed as means ± SEM. *: p<0.05, **: p<0.01, ns: not significant between LAP (n=13) vs. GB (n=8) or DS (n=5).

Figure 2: Eating behaviour.Satiety ratio (min/g) (A,B) and rate of eating (g/min) (C,D) during day- and night-time. Short-term after surgery: 3 weeks after gastric bypass (GB), 2 weeks after duodenal switch (DS) or 2–3 weeks after lapatoromy (LAP). Long-term after surgery: 14 weeks after GB, 8 weeks after DS or 8–14 weeks after LAP. Data are expressed as means ± SEM. ***: p<0.001, ns: not significant between LAP (n=13) vs. GB (n=8) or DS (n=5).

GB increased night-time energy expenditure (kcal/hr/100g body weight) at three weeks and daytime energy expenditure at 14 weeks postoperatively (Fig 3A, C). DS increased daytime energy expenditure both at two and eight weeks as well as night-time energy expenditure at eight weeks postoperatively (Fig 3B, D).

Figure 3: Energy expenditure during day- and night-time. Short-term after surgery: 3 weeks after gastric bypass (GB), 2 weeks after duodenal switch (DS) or 2–3 weeks after laparotomy (LAP). Long-term after surgery: 14 weeks after GB, 8 weeks after DS or 8–14 weeks after LAP. Data are expressed as means ± SEM. *: p<0.05, **: p<0.01, ***: p<0.001, ns: not significant between LAPGB (n=7) vs. GB (n=8) or LAPDS (n=6) vs. DS (n=5).

Overall, the results show that the increased energy expenditure took place only during night-time (relevant to active energy expenditure) shortly after GB (weeks) and switched to daytime (resting energy expenditure) after months, whereas the energy expenditure was increased during daytime shortly after DS and during both day- and night-time months after DS.

There was no change in the faecal energy density after GB. DS had severe diarrhoea within 2 weeks postoperatively, so that it was difficult to collect the faecal samples. At two months, the solid faeces were collected and the energy density was increased (Figure 4).

Figure 4: Faecal energy density. Three weeks after gastric bypass (GB) or laparotomy (LAPGB) (A) and eight weeks after duodenal switch (DS) or laparotomy (LAPDS) (B). Data are expressed as mean ± SEM. **: p<0.01, ns: not significant between LAPGB (n = 7) vs. GB (n = 8) or LAPDS (n = 6) vs. DS (n = 5).

The researchers acknowledge that there are several limitations of the study:

  • The rats used were not obese and therefore it is not known whether postsurgical effects of these two procedures are different between normal and obese rats
  • GB procedure used in rats was not exactly the same as it was applied in humans.
  • Although the size of gastric pouch after GB does not correlate with weight loss outcome in patients it cannot be excluded whether lack of the pouch in GB has impact on food intake, satiety and eating behaviour.
  • The differences between rats and humans are not only in terms of the GI anatomy but also the responses to surgery. For instance, sleeve gastrectomy only (without duodenal switch) works in some patients but not in rats.

They added that it could be interesting to directly compare the effects of sleeve only vs. sleeve with duodenal switch (one or two-staged) in the future.

Conclusion

The study shows that the rat models provide results that are in accordance with results from clinical series in patients , i.e. greater weight loss by DS than GB. Furthermore, the results reveal that different postsurgical effects of GB vs. DS in terms of food intake, eating rate, energy expenditure and absorption.

“Appropriately designed rat models provide significant insights into the mechanisms of bariatric surgery which explain well the clinical observations, e.g. that DS is superior to GB in body weight loss,” the authors conclude. “The results of the present study may suggest further that GB induces body weight loss by increasing energy expenditure, whereas DS induces greater body weight loss by reducing food intake, increasing energy expenditure and causing malabsorption.”

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