‘Exercise-Eating Linkage’ Mediated by Neuro-Endocrine Axis and the Relevance in Regulation of Appetite and Energy Balance for Prevention of Obesity

Abstract

A significant number of modern people of all ages are affected by obesity epidemic in developed and parts of developing world, resulting in immense health and financial burden (Field, 2002; Ogden et al., 2006; Orsi et al., 2011). Obesity is thought to be an independent risk factor for development of various medical conditions, such as type 2 diabetes, hypertension, dyslipidemia, and cardiovascular disease (Daniels, 2009; Fontaine, 2003; Ginsberg, 2000; Kahn & Flier, 2000; National Institutes of health [NIH], 1998), necessitating weight management for prevention and treatment of these serious diseases. Obesity epidemic reflects modern growing trends to promote excess energy intake (EI) and to discourage energy expenditure (EE) (Egger et al., 2001; Food and Agriculture Organization of the United Nations [FAO], 2003; Hill et al., 2003). Thus, it is well recognized that lifestyle intervention, such as changes in behavior by combination of reductions in EI and increases in physical activity, can achieve ideal weight control (Bray, 2008). Nevertheless, it seems impossible for most of people to fight down consciously their impulses of overeating in modern societies where they have easy access to unlimited supply of highly palatable and energy-dense food (Cohen, 2008). In such circumstance, appetite is receiving extensive attention for one of key factors to adjust or disrupt energy balance (EB). In particular, an important group of the intricate factors for the appetite control are gut hormone family, including ghrelin, peptide YY (PYY), glucagonlike peptide-1 (GLP-1), oxyntomodulin (OXM), and cholecystokinin (CCK) (Huda et al., 2006; Naslund & Hellstrom, 2007). Recent advances have been made in understanding the structures, sources, releasers, target organs and receptors, and how these gut hormones influence brain systems for the control of appetite and EI. In brief, these gut hormones are secreted from gastrointestinal organs in response to nutrient conditions and give signals to hypothalamic and brainstem nuclei both of which are in close anatomical proximity to a circumventricular organ with an incomplete blood-brain barrier (BBB), such as median eminence and area postrema. Ghrelin is only an orexigenic hormone and secreted shortly before meals, whereas other gut hormones are all anorectic and released into circulation postprandially in proportion to calorie intake.