The Human Obesity Epidemic - A Physiological Perspective

Neuroendocrine regulation of food intake

Despite a global obesity epidemic suggesting that human physiology is unable to prevent unhealthy gains in body weight, ample evidence indicates that weight can be tightly regulated. Food intake regulation is complex and in this article we will present a basic endocrine feedback loop model of energy homeostasis. Next, integration of long-term regulation with short-term, meal specific regulation and satiety will be discussed. Finally, the role of adiposity signals in modulation of food reward will be highlighted. A basic understanding of the structure-function of these systems will inform the challenges of clinical care for those with disorders of energy balance.

Hypothalamic proinflammatory lipid accumulation, inflammation, and insulin resistance in rats fed a high-fat diet

Weight gain induced by an energy-dense diet is hypothesized to arise in part from defects in the neuronal response to circulating adiposity negative feedback signals, such as insulin. Peripheral tissue insulin resistance involves cellular inflammatory responses thought to be invoked by excess lipid. Therefore, we sought to determine whether similar signaling pathways are activated in the brain of rats fed a high-fat (HF) diet. The ability of intracerebroventricular (icv) insulin to reduce food intake and activate hypothalamic signal transduction is attenuated in HF-fed compared with low-fat (LF)-fed rats. This effect was accompanied by both hypothalamic accumulation of palmitoyl- and stearoyl-CoA and activation of a marker of inflammatory signaling, inhibitor of kappaB kinase-beta (IKKbeta). Hypothalamic insulin resistance and inflammation were observed with icv palmitate infusion or HF feeding independent of excess caloric intake. Last, we observed that central IKKbeta inhibition reduced food intake and was associated with increased hypothalamic insulin sensitivity in rats fed a HF but not a LF diet. These data collectively support a model of diet-induced obesity whereby dietary fat, not excess calories, induces hypothalamic insulin resistance by increasing the content of saturated acyl-CoA species and activating local inflammatory signals, which result in a failure to appropriately regulate food intake.