| OBSERVATION'S |
Obesity is high on the list of some researchers, including Samuel Klein, a professor of medicine at Washington University, St. Louis. "Although, right now, obesity is not one of the criteria for the metabolic syndrome, anyone who has a large waist circumference that meets the criteria is almost always obese," he says. It is now clear that obesity is not just a matter of excess weight, because fat cells do not merely store fat: They send out bioactive molecules with powerful effects throughout the body. Some of these are low-molecular-weight proteins that induce inflammation, now considered a major cause of cardiovascular disease. For example, tumor necrosis factor- (TNF-) activates inflammatory changes in vascular tissue that promote the adhesion of monocytes, which are a type of white blood cell, to the thin lining of the blood vessels. When a monocyte stuck to the blood vessel penetrates the lining, it becomes a macrophage that feeds on low-density lipoproteins in the plasma. The accumulation of macrophages begins an atherosclerotic plaque. TNF- also interferes with insulin signaling and causes insulin resistance. Angiotensinogen is the precursor to angiotensin II, which constricts blood vessel walls and raises blood pressure. In addition, it enhances macrophage accumulation as well as the metabolism of nitric oxide into free radicals. NO counters the effects of angiotensin II: It dilates blood vessel walls and protects them from macrophage adhesion. Plasminogen activator inhibitor-1 slows the dissolution of blood clots. High levels of PAI-1 make it more difficult to remove blood clots, increasing the risk of a heart attack or stroke. Other chemical messengers from fat cells help regulate energy balance. For example, leptin signals the brain that the body has enough fat stores and encourages the body to burn calories faster. |
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