Authors at the Institute of Biological and Health Sciences in Brazil looked through current literature on obesity, diabetes and related search terms to review the mechanisms involved in the biological mechanism of obesity and insulin resistance. They aimed to link changes in white AT with the development of type 2 diabetes and discuss if reduction in risk of co-existing disorders resulting from weight loss is due to a decrease in inflammatory agents.
Adipose tissue
The authors said that there is currently limited knowledge about how AT relates to obesity.
AT develops during pregnancy and can expand throughout life in response to increased food intake, resulting in adipocyte cell growth. AT plays a vital role in regulating how much fat from our diet reaches the circulation.
In obesity, adipocytes may reach their limits and not be able to store any more lipids which then exposes other tissues to them. Excess lipids in the bloodstream and accumulation in organs such as the pancreas, liver and muscle seem to contribute to the development of insulin resistance in overweight people said the authors.
Mechanisms discussed
They discussed the differences between ‘metabolically healthy obese individuals’ and unhealthy obesity. Increase in adipocyte cell numbers, where there are many small fat cells (as compared to cell growth and bigger fat cells) may be a key mechanism as this results in normal glucose metabolism.
Indeed, they commented that a factor involved in the development of Type 2 diabetes mellitus (T2DM) seems to be the failure of cell differentiation in the adipocyte. They wrote “It seems that when cell size reaches a critical threshold, adipocytes decrease the transport of fatty acids stimulated by insulin to AT. This negative feedback can protect the adipocytes against excessive lipid accumulation and restrict the expansion of AT, which leads to obesity and associated metabolic complications.”
The review also discussed impaired post-prandial blood flow in AT, causing lipids to remain longer in the circulation, and hypoxia. These factors can be linked to inflammation and insulin resistance.
'Weight loss is the key factor'
The authors concluded that although the network connecting obesity to diabetes may be complex, understanding it may allow strategies to treat and prevent these diseases.
They wrote: “Various mechanisms are involved in the pathogenesis of insulin resistance linked to disorders caused by obesity. However, weight loss is the key factor to reverse the situation to a healthy state before the installation of T2DM”.
They said that there is currently no consensus about the effects of different amounts of macronutrients or the amount of weight loss needed to beneficially change the inflammatory markers and more research is needed in this area.
Source: Nutrition Research Reviews
2015 Dec;28(2):121-132 doi:10.1017/S0954422415000098
“Obesity and diabetes: the link between adipose tissue dysfunction and glucose homeostasis”
Authors: M.V. Abranches, F.V. Esteves de Oliveira, L. Lopes da Conceicao and M. do Carmo Gouveia Peluzio