Questions and Answers

Proopiomelanocortin (POMC) is converted into alpha-melanocyte-stimulating hormone (alpha-MSH), which acts centrally on the melanocortin receptor 4 (MC 4) to reduce dietary intake. Genetic defects in POMC production and mutations in the MC4 gene are described as monogenic causes of obesity in humans. Of particular interest is the fact that patients with POMC mutations tend to […] Read More

The strong heritability of obesity has been demonstrated in several twin and adoptee studies, in which obese individuals who were reared separately followed the same weight pattern as that of their biological parents and their identical twin. Metabolic rate, spontaneous physical activity, and thermic response to food seem to be heritable to a variable extent. […] Read More

Two major groups of factors, genetic and environmental, have a balance that variably intertwines in the development of obesity. Genetic factors are presumed to explain 40-70% of the variance in obesity, within a limited range of BMI (18-30 kg/m2). A study in which monozygotic twins were overfed by 1000 kcal per day, 6 days a […] Read More

Mutations resulting in defects of the leptin receptor in the hypothalamus may occur. These mutations result in early-onset obesity and hyperphagia despite normal or elevated leptin levels, along with hypogonadotropic hypogonadism, and defective thyrotropin secretion. Murray et al first reported on a sequence variant within the leptin gene that enhances the intrinsic bioactivity of leptin, […] Read More

Patients with the night-eating syndrome have an attenuation of the nocturnal rise in plasma melatonin and leptin levels and higher circadian levels of plasma cortisol. These individuals have morning anorexia, evening hyperphagia, and insomnia. In one study, patients with night-eating syndrome averaged 3.6 awakenings per night; 52% of these awakenings were associated with food intake, […] Read More

Friedman and colleagues discovered leptin (from the Greek word leptos, meaning thin) in 1994 and ushered in an explosion of research and a great increase in knowledge about the regulation of the human feeding and satiation cycle. Leptin is a 16-kD protein produced predominantly in white subcutaneous adipose tissue and, to a lesser extent, in […] Read More

Smell plays an important role in feeding behavior. Differences in the odor detection threshold (i.e., the lowest concentration of a substance detectable by the human olfactory sense) were found in a study that measured thresholds in 8 lean, fasted individuals before and during a 2-hour hyperinsulinemic-euglycemic insulin clamp. Increased insulin led to reduced smelling capacity, […] Read More

In addition to neurotransmitters and neurogenic signals, many hormones affect appetite and food intake. Endocannabinoids, through their effects on endocannabinoid receptors, increase appetite, enhance nutrient absorption, and stimulate lipogenesis. Melanocortin hormone, through its effects on various melanocortin receptors, modifies appetite. Several gut hormones play significant roles in inducing satiety, including glucagon-like peptide-1 (GLP-1), neuropeptide YY […] Read More

Critical enzymes involved in adipocyte metabolism and function include the following: Endothelial-derived lipoprotein lipase – Lipid storage; Hormone-sensitive lipase – Lipid elaboration and release from adipocyte depots; Acyl-coenzyme A (acyl-CoA) synthetases – Fatty acid synthesis. In addition, a cascade of enzymes is involved in beta-oxidation and fatty acid metabolism. The ongoing flurry of an investigation […] Read More

Proinflammatory products of the adipocyte include the following: Tumor necrosis factor-alpha; Interleukin 6; Monocyte chemo attractant protein–1 (MCP-1). Other adipocyte products include the following : Lipotransin; Plasminogen activator inhibitor-1 (PAI-1) – Associated with cardiovascular risk; Adipocyte lipid-binding protein; Acyl-stimulation protein; Prostaglandins; Adipsin; Perilipins; Lactate; Leptin – Appetite regulator; Adiponectin – With a major role in […] Read More