|BMI is not a good predictor of metabolic health. One reason it isn't is the differential contribution of visceral and subcutaneous body fat on diabesity an CVD risk. The rodent study at hand demonstrates that quite drastically.|
As Hocking et al. (2014) highlight in their latest paper, "[t]his relationship [between VAT, type 2 diabetes, dyslipidaemia and hypertension] was originally attributed to increased NEFA [non-esterified fatty acid] flux from VAT into the portal circulation" (Hocking. 2014).
A closer look at the low relative contribution of VAT to the total NEFA concentration in our blood does yet suggest that other factors, such as the proinflammatory cytokine production that is particularly pronounced in visceral (vs. subcutaneous) would be at least as important as the constant efflux of non-esterified fatty acids.
To probe the differential acute and chronic effects of subcutaneous (non-inflammatory) and visceral adipose tissue on glucose metabolism and whole body inflammation, researchers from the Garvan Institute of Medical Research in Australia conducted an interesting experiment in which they performed time course studies to investigate the short- and long-term effects of inguinal subcutaneous→visceral (SubQ→Vis) and epididymal visceral→visceral (Vis→Vis) adipose tissue transplantation in HFD-fed mice.
|Figure 1: The transplantation of subcutaneous fat into the intra-abdominal cavity of the mice did not just improve the glucose tolerance it did also (albeit non-significantly) blunt the HFD-induced weight gain (Hocking. 2014).|
Yes, the study at hand does also underline the fallacies of liposuction: Unlike lifestly-induced weight loss that will target both visceral and subcutaneous body fat (for the obese the visceral fat will usually go first), liposuction will remove only subcutaneous fat. It is thus not surpFrising that liposuctions will have no effect on insulin action and risk factors for coronary heart disease (Klein. 2004). With significant increases of 16% (range 13 to 21 percent) in women and 13 (10-17%) of the visceral to subcutaneous fat ratio, as they were observed by Matarasso et al. (1998), and post-liposuction gains in total visceral fat, the removal of unaesthetic subcutaneous fat may eventually even worsen a patients' metabolic health (assuming the liposuction is not complemented by profound lifestyle changes | no energy surplus, no fat gain!).Now, what is intriguing, though, is that "sick" were only those rodents who had been transplanted with metabolically active and highly inflammatory visceral fat. The rodents who harbored an additional 13% of formerly subcutaneous fat in their abdominal cavity actually experienced significant improvements in glucose tolerance and inflammation within the 6 week post-transplantation study period and that despite the fact that they received the same obesogenic high energy + high fat diet as the rodents who were sham operated or received visceral donor fat.
A closer examination of the underlying mechanisms revealed that the SAT transplantation prevented HFD-induced hepatic triacylglycerol accumulation and normalised the expression of hepatic gluconeogenic enzymes.
"Grafted fat displayed a significant increase in glucose uptake and unexpectedly, an induction of skeletal muscle-specific gene expression. Mice receiving subcutaneous fat also displayed a marked reduction in the plasma concentrations of several proinflammatory cytokines (TNF-α, IL- 17, IL-12p70, monocyte chemoattractant protein-1 [MCP-1] and macrophage inflammatory protein-1β [ΜIP-1β]), compared with sham-operated mice. Plasma IL-17 and MIP-1β concentrations were reduced from as early as 4 weeks after transplantation, and differences in plasma TNF-α and IL-17 concentrations predicted glucose tolerance and insulinaemia in the entire cohort of mice (n=40)" (Hocking. 2014).That's in contrast, mice receiving visceral fat transplants who were glucose intolerant, with increased hepatic triacylglycerol content and elevated plasma IL-6 concentrations.
- Hocking, Samantha L., et al. "Subcutaneous fat transplantation alleviates diet-induced glucose intolerance and inflammation in mice." Obesity Research & Clinical Practice 8 (2014): 99-100.
- Klein, Samuel, et al. "Absence of an effect of liposuction on insulin action and risk factors for coronary heart disease." New England Journal of Medicine 350.25 (2004): 2549-2557.
- Matarasso, Alan, Richard W. Kim, and John G. Kral. "The impact of liposuction on body fat." Plastic and reconstructive surgery 102.5 (1998): 1686-1689.
- Oliveros, Estefania, et al. "The concept of normal weight obesity." Progress in cardiovascular diseases 56.4 (2014): 426-433.