NUTRITION
October 1, 1999

Where's the Fat?

We are constantly reminded to watch our weight. Our social and personal well-being, our happiness and health, we are told, all benefit from weighing less. It is certainly true that if you are obese you are more likely to suffer from some diseases, such as diabetes and heart disease. Recently, however, it has become apparent that the site of fat (adipose) tissue accumulation may be as important a risk factor as how much fat you have - perhaps more important.

Body Fat Distribution
As early as 1956, a French physician noted that adipose tissue was distributed differently in men and women. He coined the term 'android' to describe the upper body (abdominal) distribution and 'gynoid' for the lower body (gluteo-femoral) fat accumulation more commonly seen in women. Furthermore, he observed that there was an increased association of android, i.e., abdominal obesity, with diabetes mellitus, coronary artery disease and gout.

Diseases Influenced by Fat Distribution
Little progress was made in understanding this information until the 1980s when investigators began to explore the metabolic implications in more detail. In numerous studies, it was found that the distribution of adiposity in the upper body or abdominal region was associated with potent disease processes:
  1. Impaired glucose tolerance
  2. Insulin resistance, fasting hyperinsulinemia
  3. Hypertriglyceridemia, hypercholesterolemia and low HDL cholesterol
  4. Diabetes mellitus
  5. Coronary artery disease
  6. Hypertension
  7. Hyperuricemia
  8. Stroke

Although abdominal obesity is often accompanied by whole body obesity, abdominal obesity, on its own, increases your chances of suffering from these diseases.

How Do You Measure Abdominal Obesity?
The classical measure for upper and lower body obesity is the Waist-Hip-Ratio (WHR). This crude measurement uses the simplest of methods — a tape measure — and is expressed as a ratio. The waist is measured at its narrowest point and the hip circumference at its widest, while standing. For example, a person with a 30" (76 cm) waist and 36" (91 cm) hips would have a ratio of 5/6 (.83). Normal values depend on age and technique of measurements but, in general, increased risk is considered to occur with a WHR greater than 0.8 for females and more than 0.95 for males.

Attempts to standardize the WHR measurement have been developed in recent years. Abdominal CT scans and magnetic resonance imaging (MRI) of intra-abdominal adipose depots have been used in metabolic studies and are very accurate. But they are too expensive and impractical to be used more widely.

Why Do Patterns of Adipose Tissue Distribution Occur?
Genes and hormones appear to be the two major influences affecting accumulation of fat. Identical twin studies and other population studies indicate an estimated 20-50% genetic influence upon body fat distribution. The genes responsible for this have not been identified.

Because the site of fat deposition differs so dramatically between women and men, we know that hormonal factors must play a role. Estrogen and prolactin, predominantly female hormones, appear to promote fat deposition in the gluteo-femoral region. Corticosteroids may also contribute to abdominal fat stores. We see this in patients with Cushing's syndrome, a disease of increased corticosteroid production, who, typically, have upper body obesity.

How Fat Cells Differ
Fat tissue is not uniform in its metabolic characteristics. Fat cells from the organs are more likely to break down (lipolysis) under the influence of catecholamines (brain transmitters like epinephrine). Making matters worse, these abdominal fat cells do not allow insulin to come to their rescue and slow their breakdown. Fat cell breakdown liberates free fatty acids (FFA) from the cell. While FFA are important metabolic fuels, they may well be the villains in a number of metabolic scenarios. It is suspected that FFA prevent the body from using glucose, which may cause insulin resistance and glucose intolerance, excessively high levels of insulin in the blood (hyperinsulinemia) and increased glucose production by the liver, a typical finding in Type II diabetes mellitus. FFA's also stimulate the synthesis of triglycerides in the liver, VLDL (very-low density lipoprotein) and also the so-called bad cholesterol, low density lipoprotein (LDL).

What Can You Do?
The influence of diet, drugs and exercise to diminish abdominal obesity has been evaluated in separate studies. Diet appears to influence all body fat depots, although some studies seem to indicate a greater degree of weight loss from the abdominal region in those subjects who start out with an increased upper body obesity. Exercise has been shown in some studies to have a beneficial effect upon abdominal weight loss. Little data are available on the effects of drugs at this time, although new information is emerging that suggests that drug treatment may have specific effects on intra-abdominal fat. On the other hand, people with predominant gluteofemoral fat accumulation (aka "thunder thighs") may be counseled that their problem is more aesthetic than health-related.

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