Relative Energy Expenditure Decreases during the First Year after Bariatric Surgery: A Systematic Review and Meta-Analysis

Triiodothyronine (T3) promotes browning of white adipose through inhibition of the PI3K/AKT signalling pathway

Obesity arises from an imbalance between energy consumption and energy expenditure, and thyroid hormone levels serve as a determinant of energy expenditure. We conducted experiments at the animal and cellular levels and combined those findings with clinical data to elucidate the role of triiodothyronine (T3) in facilitating the browning of white adipose tissue (WAT) and its underlying mechanism. The results showed (i) the impaired metabolic function of local WAT and the compensatory elevation of systemic thermogenesis in obesity; (ii) T3 treatment of white adipocytes in vitro and local WAT in vivo induced a shift towards a morphologically "brown" phenotype, accompanied by upregulation of mRNA and protein expression of browning-related and mitochondrial function markers, which suggest that T3 intervention promotes the browning of WAT; and (iii) the aforementioned processes could be modulated through inhibition of the PI3K/AKT signalling pathway; however, whether T3 affects the PI3K/AKT signalling pathway by affecting insulin signalling remains to be studied and clarified. The results of our study indicate that T3 treatment promotes browning of WAT through inhibition of the PI3K/AKT signalling pathway; these findings offer novel perspectives regarding the potential of localised therapies for addressing WAT volume in individuals with obesity.

Single-anastomosis duodeno-ileal bypass with sleeve gastrectomy improves lipid and glucose homeostasis in ob/ob mice

OBJECTIVE

The objective of this study was to compare the general and metabolic impact of single-anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S) with Roux-en-Y gastric bypass (RYGB) in an obese (ob/ob) mouse model.

METHODS

10-week-old male ob/ob mice underwent either SADI-S, RYGB, or laparotomy surgery (Sham group). General and metabolic parameters were assessed during a 5-week period thereafter.

RESULTS

SADI-S induced a deeper weight loss ([mean ± SEM] -41.2% ± 3.3%) than RYGB (-5.6% ± 3.5%, p < 0.001) compared with the Sham group (+6.3% ± 1.0%, p < 0.05). A significant food restriction was observed after SADI-S only (-31%, 117.4 ± 10.3 g vs. 170.2 ± 5.2 g of food at day 35 in Sham group mice, p < 0.001). Random-fed glycemia and glucose tolerance were more improved after SADI-S than RYGB. SADI-S decreased plasma cholesterol concentration by 60% (0.49 ± 0.04 g/L vs. 1.40 ± 0.10 g/L in the Sham group at day 35, p < 0.01), significantly more than RYGB (1.04 ± 0.14 g/L, p = 0.018). Plasma sitosterol/cholesterol and campesterol/cholesterol ratios were decreased after SADI-S, suggesting a reduced intestinal cholesterol absorption. SADI-S increased exogenous plasma cholesterol-D7 clearance and fecal elimination, also indicating an increased plasma cholesterol excretion. Studying a pair-fed group demonstrated that calorie restriction alone did not explain the beneficial impact of SADI-S.

CONCLUSIONS

SADI-S is associated with a greater improvement in lipid and glucose homeostasis than RYGB in ob/ob mice.

Mechanisms of Action of Bariatric Surgery on Body Weight Regulation

Bariatric surgery is an effective treatment modality for obesity and obesity-associated complications. Weight loss after bariatric surgery was initially attributed to anatomic restriction or reduced energy absorption, but now it is understood that surgery treats obesity by influencing the subcortical areas of the brain to lower adipose tissue mass. There are three major phases of this process: initially the weight loss phase, followed by a phase where weight loss is maintained, and in a subset of patients a phase where weight is regained. These phases are characterized by altered appetitive behavior together with changes in energy expenditure. The mechanisms associated with the rearrangement of the gastrointestinal tract include central appetite control, release of gut peptides, change in microbiota and bile acids. However, the exact combination and timing of signals remain largely unknown.

Mechanisms of Weight Loss After Obesity Surgery

Obesity surgery remains the most effective treatment for obesity and its complications. Weight loss was initially attributed to decreased energy absorption from the gut but has since been linked to reduced appetitive behavior and potentially increased energy expenditure. Implicated mechanisms associating rearrangement of the gastrointestinal tract with these metabolic outcomes include central appetite control, release of gut peptides, change in microbiota, and bile acids. However, the exact combination and timing of signals remain largely unknown. In this review, we survey recent research investigating these mechanisms, and seek to provide insights on unanswered questions over how weight loss is achieved following bariatric surgery which may eventually lead to safer, nonsurgical weight-loss interventions or combinations of medications with surgery.

The magnitude and progress of lean body mass, fat-free mass, and skeletal muscle mass loss following bariatric surgery: A systematic review and meta-analysis

Postbariatric loss of muscle tissue could negatively affect long-term health due to its role in various bodily processes, such as metabolism and functional capacity. This meta-analysis aimed to unravel time-dependent changes in the magnitude and progress of lean body mass (LBM), fat-free mass (FFM), and skeletal muscle mass (SMM) loss following bariatric surgery. A systematic literature search was conducted in Pubmed, Embase, and Web of Science. Fifty-nine studies assessed LBM (n = 37), FFM (n = 20), or SMM (n = 3) preoperatively and ≥1 time points postsurgery. Random-effects meta-analyses were performed to determine pooled loss per outcome parameter and follow-up time point. At 12-month postsurgery, pooled LBM loss was -8.13 kg [95%CI -9.01; -7.26]. FFM loss and SMM loss were -8.23 kg [95%CI -10.74; -5.73] and -3.18 kg [95%CI -5.64; -0.71], respectively. About 55% of 12-month LBM loss occurred within 3-month postsurgery, followed by a more gradual decrease up to 12 months. Similar patterns were seen for FFM and SMM. In conclusion, >8 kg of LBM and FFM loss was observed within 1-year postsurgery. LBM, FFM, and SMM were predominantly lost within 3-month postsurgery, highlighting that interventions to mitigate such losses should be implemented perioperatively.

Effects of Resistance Training With or Without Protein Supplementation on Body Composition and Resting Energy Expenditure in Patients 2-7 Years PostRoux-en-Y Gastric Bypass: a Controlled Clinical Trial

BACKGROUND

Resistance training (RT) and adequate protein intake are recommended as strategies to preserve fat-free mass (FFM) and resting metabolic demand after bariatric surgery. However, the effect of both interventions combined in the late postoperative period is unclear. This study investigated the effects of RT, isolated and combined with protein supplementation, on body composition and resting energy expenditure (REE) in the late postoperative period of Roux-en-Y gastric bypass (RYGB).

METHODS

This controlled trial involved patients who were 2-7 years postRYGB. Participants were partially matched on body mass index (BMI), age, sex, and years after surgery, and divided into four groups, placebo maltodextrin (control [CON]; n = 17), whey protein supplementation (PRO; n = 18), RT combined with placebo (RTP; n = 13), and RT combined with whey protein supplementation (RTP + PRO; n = 15)-considering the participants who completed the protocol. REE was measured by indirect calorimetry and body composition by multifrequency electrical bioimpedance.

RESULTS

Participant characteristics (40.3 ± 8.3 years old; average BMI 29.7 ± 5.3 kg/m²; 88.9% females) were similar among groups. The RTP+PRO group showed an increase of 1.46 ± 1.02 kg in FFM and 0.91 ± 0.64 kg in skeletal muscle mass (SMM), which was greater than the equivalent values in the CON group (- 0.24 ± 1.64 kg, p = 0.006 and - 0.08 ± 0.96 kg, p = 0.008, respectively). There was no significant time-by-group interaction for absolute or relative REE.

CONCLUSION

Combined RT and adequate protein intake via supplementation can increase FFM and SMM in the late postoperative period without changing REE. These associated strategies were effective in improving muscle-related parameters and potentially in improving the patients' physical function.

Do Bariatric Surgeries Enhance Brown/Beige Adipose Tissue Thermogenesis?

Bariatric surgeries induce marked and durable weight loss in individuals with morbid obesity through powerful effects on both food intake and energy expenditure. While alterations in gut-brain communication are increasingly implicated in the improved eating behavior following bariatric surgeries, less is known about the mechanistic basis for energy expenditure changes. Brown adipose tissue (BAT) and beige adipose tissue (BeAT) have emerged as major regulators of whole-body energy metabolism in humans as well as in rodents due to their ability to convert the chemical energy in circulating glucose and fatty acids into heat. In this Review, we critically discuss the steadily growing evidence from preclinical and clinical studies suggesting that Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), the two most commonly performed bariatric surgeries, enhance BAT/BeAT thermogenesis. We address the documented mechanisms, highlight study limitations and finish by outlining unanswered questions in the subject. Further understanding how and to what extent bariatric surgeries enhance BAT/BeAT thermogenesis may not only aid in the development of improved obesity pharmacotherapies that safely and optimally target both sides of the energy balance equation, but also in the development of novel hyperglycemia and/or hyperlipidemia pharmacotherapies.