Do Bariatric Surgeries Enhance Brown/Beige Adipose Tissue Thermogenesis?

Abstract

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.

Induction of Adipose Tissue Browning as a Strategy to Combat Obesity

“…However, this hypothesis should be supported by experiments mice with BAT-specific GPBAR-1 knockout. Present evidence does not support the role of gut hormones in the induction of post-bariatric surgery thermogenesis [ 117 ]. However, the postoperative changes in the intestinal microflora can contribute to bariatric surgery’s beneficial effects, especially that dysbiosis induced by antibiotic exposure was found to attenuate weight loss and metabolic improvement following VSG [ 119 ].…”

“…Interestingly, rodent and human studies suggest that the effect of bariatric surgery on AT browning may depend on the procedure: while Roux-en-Y gastric bypass (RYGB) mainly enhances beige cell recruitment, and vertical sleeve gastrectomy (VSG) predominantly increases BAT thermogenesis. Moreover, the thermogenic effect depends on the fat content in the diet and is absent if postoperatively, a low-fat diet is applied [ 117 ].…”

“…However, it should be underlined that the postsurgical increase in BAT thermogenesis and WAT browning are less markedly indicated in humans than in rodents [ 117 ]. Moreover, it is not clear to what extend the thermogenic effect of bariatric surgery contributes to the postoperative changes in weight and metabolic parameters.…”

Beige Fat Maintenance; Toward a Sustained Metabolic Health

“…The effects of prolonged physical training on human scWAT browning and increasing the levels of circulating adiponectin, apelin, irisin, and FGF21 are in line with improved metabolic health (145,149). Additionally, severe weight loss in cancer patients as well as in obese patients going through weight loss surgeries leads to increased browning (150,151). Prolonged elevations in norepinephrine levels as a consequence of burn injury also leads to increased scWAT browning and thermogenesis (152).…”

A sympathetic gut connection drives the metabolic benefits of Roux-en-Y gastric bypass

“…They do, however, successfully reproduce (perhaps even too well) the post-RYGB and SG increases in resting metabolic rate reported in clinical studies [4]. Consequently, when functional brown fat was rediscovered in adult humans a little over ten years ago now [5][6][7] and white fat browning (also known as britening or beiging) gained mainstream attention by the metabolic community, it soon followed that surgical scientitsts would ask how these thermogenic and glucoregulatory tissues are affected by RYGB and SG [8]. The results would be decidedly mixed, with some evidence of enhanced brown fat thermogenesis, white fat browning, or neither, for both procedures [8].…”