You've read the story about fats over and over. Omega-3 fats from fish are good for your health and trans fats in margarine are bad. Polyunsaturated vegetable oils are good for your heart and saturated animal fats are bad. Haven't we heard enough? Well, no! That isn't where the story of fats ends. There is also something called visceral fat and too much of it also is very bad. So let's look at this new chapter in the good/bad story about fats. Did you ever wonder why excess body fat or obesity causes a host of diseases like diabetes, heart disease, high blood pressure, and asthma, and kills people? "Turn the pages..."
Visceral fat is not fat that you eat, it's fat that you make yourself. You may not be a butcher or baker, but you are a visceral fat maker. Visceral fat is the adipose tissue that surrounds the organs in your abdomen, and it has special properties different from that of body fat found elsewhere. It secretes substances that in small amounts are essential to survival, but in larger amounts can ruin your health.

Most of the time we think of body fat as simply a place where excess energy or calories are stored. Kind of an inert place like a dish of butter or a packet of olive oil hanging around waiting to be used up. That's true for subcutaneous fat located just under your skin. It stays there until you run out of food, and then it's used up to supply the missing energy that you need.

But, visceral fat is quite the opposite. Although it also stores calories, it is a thriving, metabolically active, churning, chemical factory that produces many different substances that get into your blood and circulate throughout the body. Most notably, visceral fat produces chemicals involved with inflammation. Inflammation is one of the newer buzzwords that's most often associated with a lot of bad health problems. But in reality, inflammation in small amounts is an essential process required for survival. This is what occurs when your body is injured either externally or internally. You see the inflammatory process when a wound becomes red, inflamed, hot, and sore. This occurs because many different kinds of molecules and cells race to the injury site to start the healing process. That's good. Without this, an injury would never heal.

The problem arises when you have too much visceral fat, which similar to other fat in your body increases in mass if you overeat. What you eat doesn't matter here - sugar, fat, protein - it's the amount that's important because all caloric excess is converted to fat.
Many of the potentially harmful chemicals produced by visceral fat are known. They go under such complicated names as cytokines, leukotrienes, tumor necrosis factor, interleukins, C-reactive protein, and other names best left to the biochemists to worry about. In small amounts they help cure injuries, but in large amounts they do excessive damage - they act as if the whole body has been injured.

This central obesity of belly fat is the main problem. Fat around the hips and buttocks is not such a severe health problem because it is less metabolically active than visceral fat and behaves more like subcutaneous fat. Curiously, hip fat occurs mainly due to an increase in numbers of fat cells whereas visceral fat is more related to an increase in fat cell size. Yes, even fat cells have their own personalities.

You are well aware of the plot to this story - too much visceral fat is dangerous. Have you been anticipating the conclusion? You know what it is, don't you? Does it help if we hint that visceral fat is also especially responsive to exercise? We don't have to read further as the last few lines of the story are obvious. So close the book on good/bad fats and reach your own conclusion as to what is [not] written in the final sentence. You knew this all along.

As a professor of Animal Science and Nutrition and Food Sciences at UVM, Shelburne resident, Lyn Carew, has taught more than 20,000 students. He has received many teaching awards at UVM, plus two national recognitions. He was named Carnegie Foundation Vermont Teacher of the Year in 2001. The Shelburne News is pleased to be able to share Lyn Carew's expertise in the latest nutritional information with our readers once a month.