Today's news that life expectancy has declined for 12 percent of American women (and fallen or stagnated for 4 percent of American men) can be viewed not as a sentence but as a call to action: Stop smoking, and lose weight. Besides tobacco use, the other big suspect in the disturbing drop (after a century and a half of steady rise) is that old culprit, too much fat. From a population standpoint, "obesity has become the wild card that can erase our health gains," says Majid Ezzati, lead study author and associate professor of international health at the Harvard School of Public Health. Ezzati's findings suggest that the worsening life expectancy is mostly a result of diabetes, cardiovascular disease, cancer, and chronic obstructive pulmonary disease.
In excess, fat unleashes a cascade of detrimental processes in the body; as researchers have discovered in recent years, those pudgy fat cells are not just sitting there benignly but are as active an endocrine organ as the pancreas or pituitary gland. That globular stuff's continuous communication with the rest of our bodies (including our brains) is one that cannot be ignored, since it affects our overall health significantly, as we've reported previously in our package about how fat works. In short, it causes hormones to get tipped out of balance—an oversupply of insulin, for example, leads to insulin resistance—and chronic inflammation. These processes have been linked to type 2 diabetes, certain cancers, heart disease, hypertension, and liver disease. Fat also sets off metabolic changes that make losing weight and keeping it off more tricky.