The Omentum and Abdominal Fat - Health Benefits and Problems
The Digestive System
The greater omentum is a fatty membrane that covers the small and large intestine. Until recently its only function was thought to be the storage of fat. Now researchers have discovered that it not only has other functions but also has some important health benefits. However, it seems to be a "Jekyll and Hyde" structure. If it contains too much fat it has the potential to cause serious health problems.
There are two types of fat in the abdominal area - subcutaneous fat and visceral or abdominal fat. Subcutaneous fat is located under the skin and above the muscles. It's the soft fat that we can feel when we grab hold of our skin. When people have an excessive amount of subcutaneous fat in the abdomen they may undergo liposuction surgery to remove some of it. The surgery doesn't affect the deeper visceral fat, however. This fat lies below the muscles in the omentum and around the organs.
Excess visceral fat can have a much more serious effect on our health than excess subcutaneous fat. Health experts say that those of us who have an apple-shaped body (one with excess fat in the abdomen) have a higher risk for certain health problems than those of us with a pear-shaped body (one which collects fat in the hips and thighs).
Since visceral fat is located below our abdominal muscles it may not be easy for us to detect its presence. Researchers say that monitoring our waist size is the best way to detect that visceral fat is collecting inside our abdomen.
Parts of the Stomach
The Peritoneum and the Omentum
The peritoneum and the greater omentum are membranous structures in the abdomen. The omentum is a specialized form of peritoneum.
The peritoneum is a smooth, glistening membrane on top of connective tissue. It lines the abdominal cavity and covers the organs in the abdomen. It's a continuous sheet but is given different names according to its location. The parietal peritoneum lines the inside of the abdomen and the visceral peritoneum covers the organs.
The Greater and Lesser Omentum
An omentum is a sheet-like structure made of a double layer of peritoneum. It contains a variable amount of fat.
The greater omentum is attached to the greater curvature of the stomach, which is the outer curve furthest away from the midline of the body. It hangs over the small and large intestine, resembling an apron, and then folds back on itself to attach to the transverse colon. This is a horizontal section of the large intestine under the stomach. The greater omentum is often referred to as simply "the omentum".
The lesser omentum is attached to the lesser curvature of the stomach, which is the inner curve nearest to the midline of the body. It extends over the first part of the duodenum (the start of the small intestine) and over part of the liver.
Fat Storage in the Omentum
A healthy omentum is a thin, pale yellow sheet that contains fat and has a lacy appearance. Fat is an essential substance in our body; it only becomes dangerous when it's present in excess amounts or in the wrong place.
If the omentum absorbs extra fat it becomes thicker and harder. An enlarged omentum may push the front of the abdomen outwards, producing a "beer belly" or "potbelly".
For a long time it was thought that the omentum wasn't important, except as a minor fat storage depot. Now there is evidence that it does more than just store fat and actually has very important functions.
Dr. Oz Describes the Omentum
The Omentum and he Immune System
Research has shown that the omentum suppresses certain aspects of the immune system, at least in mice. A process that occurs in a mouse's body may not happen in ours, but it often does.
A recent research project examined the effect of mouse omentum cells on mouse T cells (or T lymphocytes). T cells are a very important part of the immune system. They attack and destroy invaders such as bacteria, viruses and cells from other people.
T cells become activated in order to do their job. The researchers mixed omentum cells with activated T cells in laboratory equipment and found that the T cells died. T cells that hadn't been activated were unaffected by the omentum cells. The omentum cells apparently produced a substance that killed the activated T cells.
If this reaction occurs in humans it could be very significant. It may sound bad that T cells are killed by omentum cells, but in some human conditions - such as organ transplants and autoimmune diseases - the immune system needs to be suppressed. An autoimmune disease is one in which a person's immune system attacks their own body. The discovery that the omentum may have the ability to dampen immune system activity could lead to the creation of improved medications for suppressing the immune system.
The omentum contains "milky spots", which are collections of macrophages. Macrophages are a type of white blood cell and fight disease. The action of these macrophages may be another way in which the omentum affects the immune system.
Stem Cells in the Omentum
More and more researchers are finding evidence that the omentum functions in tissue repair and regeneration. In fact, some believe that this is the omentum's primary job. Surgeons sometimes attach bits of omentum to damaged tissues in the body. They know from experience that the omentum stimulates tissue repair, but how it does this is uncertain.
The omentum contains mesenchymal stem cells, or MSCs. Stem cells are very important because they are capable of forming other cell types, which isn't true for the other cells in our body. In lab flasks, MSCs from the omentum have produced bone cells and cells that resemble lung cells.
Finding good sources of adult stem cells is important because they have the ability to repair damage. Human embryos are a good source of stem cells, but their use is controversial because obtaining the cells kills the embryo. Obtaining stem cells from adults (harmlessly) avoids this problem.
The Benefits of Losing Visceral Fat
Dangers of Excess Visceral Fat
While the omentum seems to have some amazing and very helpful functions, there's no doubt that excess visceral fat in the omentum is dangerous. The fat cells are metabolically active and release a variety of chemicals. Some serve as messengers in the body and others trigger harmful inflammation. Fatty acids are also released from omental fat. These reach the hepatic portal vein, which transports the fatty acids to the liver.
Visceral fat increases the risk of cardiovascular disease, hypertension (high blood pressure), high fasting blood sugar, insulin resistance and type 2 diabetes. It also raises the blood level of LDL cholesterol (the bad cholesterol) and increases the risk of certain types of cancer. In addition, it seems to increase the chance of developing non-alcoholic liver disease.
Men generally have a larger tendency to develop visceral fat in the abdomen than women. However, after menopause a woman's tendency to store visceral fat increases. The tendency is also influenced by genetic factors.
Detecting The Presence of Abdominal Fat
If we don't have a beer belly, how do we know that we have too much abdominal or visceral fat? Health professionals say that our waist size is an indication that we're likely to have excess abdominal fat and may be a more accurate indicator of potential health problems than the Body Mass Index, or BMI.
For a person of average height, a waist size over thirty-five inches in females and over forty inches in males may be a danger sign. Another guideline states that a person's waist size should be no more than half their height.
More Information about Weight, Visceral Fat and Health
How to Lose Abdominal or Visceral Fat
Reducing calorie intake and getting regular, moderately intense exercise is the best way to lose abdominal fat. Severely restricting calories will probably make a diet very hard to maintain, however. The best plan is to make permanent and healthy lifestyle changes instead of "going on a diet".
Improve the Diet
Unless rapid weight loss is a medical necessity, it's a good idea to gradually substitute healthier and lower calorie foods for the high calorie foods in the diet. This plan will produce a slower weight loss than a crash diet but will probably be more successful in the long run.
Nutritionists generally recommend a diet that emphasizes unprocessed or minimally processed foods from plants and consists of vegetable, fruits, whole grains, lean protein, low-fat dairy and moderate amounts of monounsaturated and polyunsaturated fats. Even "healthy" foods may be high in calories, however, so it's important to be aware of the calorie content of foods. For example, fruit smoothies may be loaded with calories as well as nutrients.
Scientists have found that even a small amount of weight loss - five to ten percent of a person's weight - is likely to have substantial health benefits. It's a great goal to aim for even if it doesn't have a huge effect on a person's appearance. Some research indicates that visceral fat is lost before subcutaneous fat when we reduce our calorie intake.
Start An Exercise Program
Anyone starting a new exercise program should begin with relatively easy exercise sessions that last for a short period. This will reduce the chance of injury. The intensity and duration of the sessions should increase slowly over time. If someone is very overweight they should see a doctor before they start exercising.
Get Enough Sleep
Getting an adequate amount of sleep is also important in a healthy lifestyle. Interestingly, scientists have discovered that lack of sleep is linked to an increased amount of visceral fat in younger people belonging to certain ethnic groups.
The Definition of Obesity
Some scientists have suggested that we need a new definition of obesity that is based on the location of body fat. A person who looks overweight may have a lot of subcutaneous fat but not much visceral fat. This person may be healthy and have a low risk of many serious health problems. On the other hand, someone who looks thin may actually be unhealthy because they have a lot of visceral fat around their organs.
Sumo wrestlers are an example of people who look obese but are relatively healthy. Most of their fat is subcutaneous, not visceral. However, when they retire from wrestling and regular exercise, the amount of visceral fat in their body increases.
There are medical scans that can detect visceral fat, but most of us don't have access to these scans. The best that we can do is to follow a healthy lifestyle and monitor our waist size in relation to our height. Even if our waist size is appropriate, we don't know how much fat is hiding deep inside our abdomen below the omentum. A healthy lifestyle is therefore important for everyone.
© 2013 Linda Crampton
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