Obesity is a metabolic disorder and a dysfunctional regulation of body fat; it is associated with excess calories (diet and activity levels) as well as changing levels of hormones (insulin and leptin) that impact the regulation of metabolic processes.
Obesity occurs when a person consumes more calories from food than he or she burns that leads to an excess in amount of body fat. When a person consumes more calories, the energy balance tips toward weight gain and obesity. Genetic, environmental, and other factors may all play a part in obesity. However, obesity may also be associated with significant factors that impact metabolic processes and regulation, including caloric surpluses and changing levels of hormones.
Caloric surpluses include diet and activity levels. Diet rich in high amounts of energy which are not burned off through exercise or physical activity become excess energy that turns into fat. Obesity can lead to insulin resistance over time which causes diabetes.
More importantly, the changing levels of hormones also regulate metabolic processes. Hormones primarily involved in body mass regulation that decrease food intake and increase energy expenditure are insulin and leptin. Insulin stimulates the production of leptin by adipose tissue that decreases appetite and gives the feeling of satiety. Leptin then decreases the secretion of insulin and enhances tissue sensitivity to insulin, leading to glucose uptake for energy utilization or storage. When the body refuses to utilize stored fat as an energy source (insulin resistance) or there is a dysfunction in satiety (leptin resistance), metabolic disorder results and leads to obesity. The other two hormones that act on satiety center in the brain are ghrelin and PYY (peptide YY). Ghrelin, secreted by the stomach wall, brings feelings of hunger compared to peptide YY which is secreted from the small intestine and acts on receptors in the brain to decrease appetite.
Practice Questions
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Key Points
• Obesity occurs when a person consumes more calories from food than he or she burns, that leads to an excessive amount of body fat.
• Obesity is associated with significant factors that impact metabolic processes and regulation, including caloric surpluses and changing levels of hormones.
• Caloric surpluses occur when the diet rich in high amounts of energy do not burn off through exercise or physical activity that become excess energy that turns into fat.
• The changing levels of hormones also regulate metabolic processes; insulin stimulates the production of leptin that encourages satiety while leptin decreases the secretion of insulin and enhances tissue sensitivity to insulin, leading to glucose uptake for energy utilization or storage.
Key Terms
Obese: adult with a body mass index of 30 or higher
Caloric surplus: a state in which the amount of consumed calories is higher than the amount of burned calories
Leptin: a hormone that decreases appetite
Insulin: a hormone that controls levels of glucose in the body
Ghrelin: a hormone secreted in the stomach that promotes feelings of hunger
Adipose tissue: a term for loose connective tissue composed of adipocytes; its main role is to store energy in the form of fat
