Obesity, the Brain, and Cognitive Function

Introduction to Obesity

The epidemic of obesity has become pandemic as obesity now affects an exceptionally high proportion of the population worldwide. Indeed, the global extent of the obesity pandemic was formally recognized by the World Health Organization in 1997. While the rise in obesity rates was first noted in the United States, it has since spread to other industrialized nations and is even now being documented in developing countries. Estimates from [Page 810]the World Health Organization indicate that, as of 2005, at least 400 million adults (9.8%) were obese. Unlike most global health concerns, the obesity crisis is even more severe in developed nations. From 1960 to 2004, the prevalence of obesity in the United States has more than doubled among adults, from 13.3% to 32.1%, while the percentage of Americans overweight during the same period has increased from 44.8% to 66%, with most of this rise occurring since 1980.

Obesity is clinically identified based on BMI, which integrates an individual's total weight and height. The exact equation used to calculate BMI using imperial (i.e., English) units is the individual's body weight in pounds multiplied by the conversion factor 703 and then divided by the square of the individual's height in inches. Current BMI definitions classify people as overweight (preobese) when their BMI is between 25 and 29.9 and obese when BMI levels are 30 or greater. While BMI is a useful tool in clinical settings, obesity can be more generally defined as the physiological condition in which excess body fat has accumulated to an extent that can negatively affect health. This definition is based on the very strong association of obesity with myriad disease conditions, including type 2 diabetes, cardiovascular disease, gastrointestinal and respiratory difficulties, and many types of cancer. Furthermore, obesity is very closely tied to the metabolic syndrome, a clinical condition that can include combinations of increased girth (abdominal obesity), prediabetes indications (e.g., insulin resistance, hyperglycemia, hyperinsulinemia, and glucose intolerance), elevated fats in the blood (hypertryglyceridemia, hypercholesterolemia), elevated blood pressure (hypertension), and increased expression of inflammatory markers (C-reactive protein).

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