Global girths are on the rise—with some 1.5 billion adults now overweight and more than one in 10 adults obese worldwide. U.S. figures are even starker: more than half of the population weighs too much and more than one third are obese.

The causes of these conditions have turned out to be much more diverse than too much junk food and couch time. Research has now implicated factors as far-ranging as stress and the lack of quality sleep as complicit forces in the epidemic.

Using some of the latest scientific data, theVisualMD has created a collection of illustrations that elucidate the complex causes and biological ramifications of obesity.

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Good fat, bad fat
Not all fat is created equal—and our bodies do need some fat to function. Fat is crucial for the brain, for making hormones, keeping cell membranes healthy, and for providing energy and temperature regulation.

Too much of it, of course, can be deadly. Subcutaneous fat is the layer underneath the skin. Visceral fat, located within the abdomen, around vital organs, can get to be so excessive that it starts squeezing out blood and air supplies.

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The price of excess pounds
Overweight and obesity have been linked to ailments ranging from coronary artery disease to some types of cancer. And excess pounds put a great strain on medical costs—both for the health care system as a whole and the individual.

The annual cost of obesity in the U.S. has been estimated at about $147 billion, which includes time and productivity lost as well as extra medical care. And on average, people who are obese pay some 42 percent more for health care than healthy-weight individuals.

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To learn more about the science of obesity, visit theVisualMD's obesity site and explore our In-Depth Report on obesity.