Adipose Tissue aka Body Fat

Few substances are more reviled in our society than adipose tissue - body fat, in everyday English. Although excess body fat increases the risk of developing heart disease, diabetes, breast cancer, and premature death, what is often left out of most information is that we cannot live on lean tissue alone. Fat plays an essential role in maintaining the body. It is the quantity and distribution of body fat that determines whether it is beneficial or harmful to our health.

We survive from meal to meal because energy is produced from stored fat as we need it. Fifteen percent of the average woman s body weight is fat that provides readily accessible energy. Another four percent, often referred to as "sex-specific fat" because it stores energy reserved for the demands of pregnancy and breast feeding, is distributed primarily in the thighs, buttocks, and breasts. The average woman has enough stored fat to survive a 60-90 day fast.

Fat also serves a structural purpose. Approximately four percent of body weight is made up of fat in the organs, skeletal muscles, and central nervous systems. This fat is sometimes referred to as "essential fat" because these organs will stop functioning if it is depleted. Having too little fat is a health hazard. The risk of premature death begins to mount when body mass index (BMI) drops below 18. (BMI is calculated by multiplying weight in pounds by 700 and dividing the product by the square of height in inches.)

There are gender differences in fat distribution. Women tend to deposit fat on the thighs and buttocks while men deposit fat around the middle. In both cases, the tendency is due to an abundance of lipoprotein lipase - an enzyme that is necessary for fat storage - in those regions. Women have higher concentrations of lipoprotein lipase in the thighs and buttocks while men have higher concentrations in the abdomen. Because lipoprotein lipase is produced by fat cells, it preserves one s fat distribution in times of weight gain generally rendering women into "pears" and men into "apples."

The female pear and the male apple are broad generalizations. Many women may gain weight around the middle and some men may gain weight at the hips and thighs. There is a mountain of evidence that fat distribution is related to a person s hormonal levels. Women who have a higher proportion of circulating estrogen tend to have smaller waists in relation to their hips, while those who have a higher proportion of androgens to estrogens tend to have higher waist/hip ratios as well. This tendency has been demonstrated in studies of women with polycystic ovary syndrome, a disorder characterized by relatively low concentrations of circulating estrogen. Moreover, postmenopausal women who are not taking estrogen may experience a "middleage spread" even though their weight remains stable.

Research has linked excessive abdominal fat to increased risk for certain diseases. In observational studies, women who have waist/hip ratios of 0.8 or more, or waist measurements of 30 inches or more, are at greater risk of heart disease and diabetes than are those with smaller waists. In contrast, excess fat at the hips or thighs is unrelated to disease risk in women who have BMIs of 25 or less. It is not the "spare tire" (subcutaneous fat) that makes the apple shape insidious, but the visceral fat, a deeper layer of adipose tissue that cushions the abdominal organs. In studies of patients in whom visceral fat was measured directly by CT scan or dual photon xray absorptiometry (DXA), excess visceral fat emerged as an independent risk factor for diabetes and heart disease.

Visceral fat is directly linked with higher levels of total cholesterol and LDL ("bad") cholesterol and lower levels of HDL ("good") cholesterol. One theory is that the chemical by-products of fat metabolism are emptied into the vessels of the abdomen and are circulated to the liver, where they influence the production of blood lipids. Visceral fat has also been associated with insulin resistance. In that condition, the body does not respond adequately to insulin, the pancreatic hormone that enables glucose to enter the cells. The glucose level in the blood rises and with it, the risk of diabetes.

Ethnicity also plays a role in fat distribution. Extensive studies have been done over the last three decades comparing African-American and Caucasian women. Although African-American women tend to have greater bone density and muscle mass than Caucasian women, they also have a higher rate of obesity and a greater tendency to develop visceral fat and therefore a higher risk of heart disease and diabetes. The rounded abdomen is associated not only with the male physique but also with men s health risks. Thus, women who have waist/hip ratios above 0.8 begin to take on the male risk profile. Exercise and diet changes may help to correct the situation.

• Exercise Regular activity is now accepted as the key to weight loss and control. Data from the National Weight Control Registry indicate that women who maintain a substantial weight loss for more than three years use an average of 400 calories a day through regular exercise of all types. A survey done in England found that women who took regular brisk walks -"brisk" meaning a rate of at least 4 miles per hour - had proportionately smaller waistlines than sedentary women of the same weight. Although moderate to rigorous exercise may be necessary to reduce abdominal fat stores, there is increasing evidence that people who are 20 percent or more above their desirable weight may benefit from even such low-intensity exercise as walking at a rate of 2 miles per hour for 30 minutes a day - if they do it on a regular basis.
  If you are overweight and have an apple shape, a reasonable approach is to begin to exercise at a comfortable rate and gradually build up to higher-intensity workouts. If you are not overweight but are gaining weight around the abdomen, try exercising at a higher rate for at least 30 minutes a day.

• Diet Both the number of calories consumed and the number of calories expended through activity determine the amount of energy stored in fat. As millions of Americans know from riding the dieting rollercoaster, very low-calorie diets can bring about weight loss, but the lost pounds are just as quickly regained. The reason? As weight falls, so do lipoprotein lipase levels and the basal metabolic rate - the number of calories required to sustain body functions. When dieters begin to eat a maintenance level, metabolic rate does not increase as much as lipoprotein lipase production does.
  The typical dieter goes from three meals a day to a toast and fruit breakfast, a salad lunch, and a half-sized dinner and is rewarded with rapid weight loss during the first few weeks. The human body is remarkable. Sensing that its survival is at stake, it begins to store more fat. In essence, the diet has "taught" the body to become more efficient at storing fat! There is a way to get around the body s survival mode. Instead of drastically cutting calories all at once, gradually reduce calories, but focus mainly on changing the types of foods you consume. The emphasis should be placed on substituting foods that require the body to use more stored calories to digest them rather than reducing calories. In general, carbohydrates and proteins consume more energy in the digestive process than fats do and complex carbohydrates take more energy to digest than simple carbohydrates. Eat smart to lose those pounds for good!