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When it comes to managing the health of obese patients, doctors probably should be concerned less about how much fat is present, and worried more about where the fat is stored.

That’s the approach of endocrinologists who are educating their patients and front-line peers about the increased risks of visceral adiposity.

As opposed to the insulating subcutaneous fat that is carried on the buttocks or thighs, visceral fat in the abdominal cavity creates a much greater possibility of metabolic syndrome, according to Dr. Anthony Morrison, professor in the Division of Endocrinology at the University of South Florida (USF) College of Medicine, and co-director of the college’s Diabetes Center.

“The lower thigh fat tends to be more like a thermal shield primarily in the … tissue right underneath the skin, whereas the abdominal fat is metabolically active and is primarily around the organs in the abdominal cavity,’’ Morrison said. People with visceral fat, also known as deep belly fat, are “more prone to insulin resistance and metabolic syndrome,’’ he said.

The major components of metabolic syndrome are obesity, lipids abnormalities (especially in triglyceride levels and a decrease in HDL cholesterol), and a tendency toward elevations in blood pressure and diabetes, Morrison said.

“The most important aspect of all this is that in combination of those factors, not for any single one, it puts the person at significantly increased risk for premature cardiovascular disease,’’ Morrison said.

To appreciate the added threat of co-morbidities that visceral adiposity presents, primary care physicians must understand the role fat plays in the body. “In the past,’’ Morrison said, “fat was just thought to be a repository of excess calories. Now it is known to be a metabolically active and very important endocrine organ. It makes hormones that act differently and are … released in either an increased or decreased amount in relationship to the insulin resistance.’’

When the fat is released from the tissues inside the abdomen, it goes directly into the portal system, which drains the GI tract and goes right into the liver, which, Morrison said, is the “mother organ, from a metabolism point of view.’’

“Just like cardiologists think the heart is the most important organ in the body, many metabolics (physicians) think the liver is the most important organ in the body,’’ he said.

Dr. Cynthia Buffington is program developer for Florida Hospital’s weight management program, which will begin in early 2008 at Celebration Health near Orlando. She explained that because visceral adipose tissue has greater lypolytic activity, it is not as sensitive to insulin as subcutaneous fat, causing a much greater turnover of visceral fat directly into the portal system. That exposes the liver to very high amounts of free fatty acids, Buffington said.

“Free fatty acids, in turn, can increase the production of glucose, causing elevated blood sugar,’’ Buffington said. “Up to 80 percent of insulin is cleared by the liver before the periphery system even sees it. If it’s not cleared by the liver appropriately, it can lead to very high periphery insulin levels and insulin resistance.’’

Buffington said elevated free fatty acids also cause dyslipidemia, marked by elevated triglycerides, low HDL and more of the atherogenic LDL cholesterol lipoproteins.

Knowing the danger it presents to patients, physicians continue to seek reliable methods by which to determine the extent of visceral adiposity.

“The most easily measured marker is C-reactive protein,’’ said Morrison. “It’s probably just a surrogate marker for more important ones, like matrix metalloproteinases, plasminogen-activated Factor 1, or the more recent RBP4 (retinol-binding protein 4). Those all measure increases in insulin resistence,’’ he said.

Another test for visceral fat measures reductions in adiponectin, a hormone which, Buffington said, is “important to help reduce inflammation and vascular disease and … prevention of conditions that can lead to diabetes.’’

Morrison thinks the binding protein RBP4 will become a more widely used assessment tool for visceral adiposity, but acknowledges that most commercial blood labs don’t offer the test. “It’s used mainly as a research tool,’’ he said.

Buffington also thinks measuring RBP4 has potential, although she emphasizes it is “just one of many, many products of elevated adipose tissue that can lead to inflammation, cardiovascular disease, insulin resistance and metabolic disease.’’

“What is interesting about this particular binding protein,’’ Buffington continued, “is that it is higher in individuals (who have visceral adiposity) who are both lean and obese, and it is elevated in people who have Type II diabetes, whether they are lean or obese. It has even been found to be elevated in the relatives of people with Type II diabetes who have a genetic susceptibility to develop the disease,’’ she said.

Once visceral adiposity has been diagnosed, the challenge is treating it.

“The best treatment, and the one that is most difficult to accomplish, is that of lifestyle change,’’ said USF’s Morrison. “Diet and exercise, with the help of a nutritionist and nurse educators, are extremely (effective). There are some medications that have been shown to affect one or more of those components. But some of the controversy for metabolic syndrome in the past two or three years is that we tend to focus on one particular aspect, such as blood sugar, or lipids, or hypertension, whereas it’s really like a jigsaw puzzle and all the pieces have to fit in. Unfortunately, in addition to lifestyle, that frequently takes polypharmacy.’’

“The thing that we in the healthcare biz emphasize least well is the value of exercise,’’ Morrison said. “Exercise, per se, is important not just to burn off calories, but it is very important to decrease the components of insulin resistance syndrome.’’

Buffington said that “one of the major ways to reduce visceral adiposity is anti-stress therapy’’ because “stress, stimulates the hypothalamic-pituitary-adrenal axis,’’ she said. That leads to an increase in the “stress hormone cortisol because visceral fat, unlike subcutaneous fat, has a concentration of cortisol receptors. Cortisol, in turn, increases the numbers and size of fat cells in visceral depots.’’

Buffington noted that any manner of weight loss, whether from diet, exercise, pharmaceuticals or bariatric surgery, “leads to a preferential loss of visceral fat and significant improvement in health.’’ In other words, even though visceral tissue, which Buffington also referred to as “killer fat,’’ is the “most deadly,’’ it also is the easiest to lose.

That, no doubt, is hopeful news for patients who are serious about overcoming their obesity.



January 2008

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