Energy expenditure from BPDS betters RYGB, linked to weight loss

Biliopancreatic Diversion with Duodenal Switch (BPDS) results in greater weight loss compared with Roux-en-Y Gastric Bypass (RYGB) due to larger increases in energy expenditure, according to an international team of researchers. The authors of the paper, ‘Biliopancreatic Diversion is associated with greater increases in energy expenditure than Roux-en-Y Gastric Bypass’, published in PlosOne, hypothesise that enhanced and prolonged meal associated thermogenesis (MAT) and lower fat:lean mass ratios after BPDS may explain relative increases in total energy expenditure, compared to RYGB.

The researchers note that studies in rodents support the notion that the source of the increased MAT is the alimentary limb of the Roux-en-Y reconstruction into which food rapidly transits. This rapid and unregulated exposure of the alimentary limb mucosa to nutrient in the absence of gastric pre-processing or biliopancreatic secretions may induce a hypertrophic mucosal response. This not only increases local enteroendocrine cell number but also increases post-prandial metabolic demand and MAT.

As a result, the researcher theorised that BPDS would be associated with a higher total energy expenditure (TEE) relative to RYGB by examining the 24-hour TEE and its constituent components- focussing in particular on MAT in in recipients of BPDS and RYGB drawn from the randomised trial (Five-year outcomes after laparoscopic gastric bypass and laparoscopic duodenal switch in patients with body mass index of 50 to 60: a randomized clinical trial. JAMA surgery. 2015;150(4):352–61), which included 60 patients with BMI50-60 randomized to either BPDS (n=29) or RYGB (n=31). The present study included 12 female subjects from the Swedish cohort (six BPDS and six RYGB patients), examined at median four years after surgery and there were no significant differences at baseline with regards to age, BMI or fat:lean ratios and all participants were examined at similar post-operative times.

Energy expenditure was measured by indirect calorimetry over 24 hours in a metabolic chamber, in which oxygen and carbon dioxide contents in exhausted air leaving the chamber were measured constantly enabling an assessment of energy expenditure (EE) and RQ. The evening before study visit patients had a standardised dinner. Weight and height were measured in light underwear. Dual Energy X-Ray Absorptiometry (DEXA) was used to assess total, adipose and lean tissue as well as bone mass and density at study time. Baseline body composition was assessed using measurement of total body potassium. The DEXA values were used to adjust recorded energy expenditure values for total or lean tissue during the metabolic chamber study.

Outcomes

The mean reduction in BMI after BPDS versus baseline fell from 55.5 to 29.5, compared with after RYGB of 56.1 to 37.8, the median BMI reduction following BPDS was 51% greater than after RYGB (p=0.015). In addition, the median fat:lean ratios were 37.7% lower in the BPDS group relative to the RYGB group; 0.55 (0.49 to 0.79) vs 0.91 (0.74 to 1.34) respectively (p=0.008).

Differences in absolute body weight at five years between the BPDS and RYGB groups resulted in a differential ratio of fixed calorie intake (kcal) to body weight (kg) during the metabolic chamber study. After BPDS there was a higher ratio of intake to body mass over fixed meal intake; BPDS-16.3 kcal/kg versus RYGB 14.2 (p = 0.002).

The findings revealed that participants receiving BPDS had lower total cholesterol, LDL-cholesterol, HbA1c and HDL-cholesterol compared to RYGB participants. There was no evidence of differences in thyroid function or ovarian cycle and thus both factors could be excluded as confounders in the assessment of energy expenditure.

Physical activity during the 24-hour study period was comparable between the BPDS and RYGB patients; 5.4% and 6.1% (p=0.48). There were no between group differences regarding RQ analysed during the full 24-hour period (p=0.81), during BMR measurement (p=039) or in the fasting (p=0.72) or post-prandial state (p=0.48). However, an elevation in RQ from 0.78 (0.67 to 0.83) to 0.84 (0.81 to 0.92) for the BPDS group (p=0.03) and from 0.75 (0.72 to 0.81) to 0.83 (0.77 to 0.92) for the RYGB group (p=0.03) was evident between the fasting and fed state demonstrating a shift from fat to carbohydrate oxidation.

When adjusted for total tissue, the BPDS group had higher median 24-hour TEE as compared to the RYGB patients; 16.9 cal/min/kg and 14.1 cal/min/kg, respectively (p=0.015). The BPDS group also had a 24% higher total tissue normalised median of mean BMR; 14.3 cal/min/kg and 11.5 cal/min/kg, respectively (p=0.041). When adjusting for lean tissue there was no between group difference for 24-hour TEE (p=0.78) or BMR (p=0.67).

Adjusted for total tissue, the fasting median of mean EE was 17.09 cal/min/kg total tissue for BPDS and 15.34 cal/min/kg total tissue for RYGB (p=0.093). During the first post-prandial hour from 18.30 to 19.30 total tissue normalised median of mean EE and MAT were 26% (p=0.004) and 225% (p=0.04) higher in the BPDS group, compared to the RYGB group. During the second post-prandial hour from 19.30 to 20.30 total tissue normalised median of mean EE did not differ significantly versus fasting levels for either group. Unadjusted EE in the fasting state was higher in the RYGB group as compared to the BPDS group (p=0.04).

“The study demonstrates differences in weight normalised energy expenditure between RYGB and BPDS and suggests that these differences may support increased weight loss and weight loss maintenance after BPDS,” the authors conclude. “With specific reference to meal associated thermogenesis, the data bring forward the hypothesis that frequent consumption of small meals may through a summative effect, make a significant contribution to 24-hour energy expenditure and hence be operative as a driver of weight loss after bariatric surgery.”