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Healthy Obesity? Is their such a thing? BMI vs. Waist Circumference

Digestion, Heart, Men's Health, Weight loss, General | September 17, 2014 | Author: The Super Pharmacist

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Healthy Obesity? Is their such a thing? BMI vs. Waist Circumference

Obesity is a condition in which an individual acquires excess body fat. This condition has increased dramatically and palpably over the last few decades, possibly in conjunction with the meteoric rise in commercially-available, high-calorie (i.e. in terms of sugar and fat), low-cost food.

Obesity is popularly linked to many types of disease and debility and to all-cause mortality in general. It can be addressed through a 'healthier' diet and lifestyle, but for many obese patients, the ultimate solution is a procedure to surgically remove excess fat (stored in the body as adipose tissue). Commonly known as liposuction, this practice represents an ever-increasing proportion of healthcare expenditure yearly.

Healthy Obesity

Healthy obesity - is there such a thing?

Obesity research has recently uncovered an interesting development, in the form of 'healthy obesity'.

Healthy ObesityThis describes people with high or very high bodyweight who do not exhibit the metabolic disorders, e.g. diabetes type 2, linked to increased body fat. A review of 14 studies including over 9,000 'metabolically healthy obese'  subjects found that their risk of cardiovascular disease development was less than those with similar, but 'unhealthy', obesity, but more than people of similar demographics but of 'normal' weight.

Does Obesity guarantee an eartly death?

There are other problems with the perceptions of obesity as an automatic guarantee of early death or disease. Many studies observe that people of 'normal' weight may also experience the effects of metabolic disorder, e.g. high concentrations of dietary fats in the blood, the insulin resistance or type 2 diabetes. This indicates that increased body fat alone is not necessarily indicative of disease.

Measuring Obesity

The science of obesity and its effects on health may be adversely affected by the measurements used to quantify obesity. A popular example of these is body mass index (BMI), which is often erroneously associated with increased body fat.

The typical rationale of BMI as a measure of adiposity (i.e. how much body fat a person has) is flawed from a scientific and a common-sense point of view. For example, a professional rugby player may have a high BMI, but may not necessarily be overweight, and is not likely to be unhealthy or unfit. Body mass, after all, is made up by many tissues, e.g. muscle and bone, not just adipose tissue.

Improved measurements of the actual amounts of body fat may be more meaningful in quantifying the effects of obesity on health. They have also been used in studies on the links between obesity, disease and death. In addition, obesity tends to be strongly associated with some disorders such as heart disease or hypertension, which are also not segregated (or controlled for) in many studies. In other words, 'healthy' obese individuals (those with simple high adiposity), without diabetes or cardiovascular disease, are often not studied.

Measures (also known as markers) of obesity include:

Body Mass Index (BMI)

BMI is a ratio of body mass, measured in kilograms, to height (kg/h2). This variable tends to be categorised into ranges such as 'normal', 'moderate', and 'high'. This creates potential problems when used in research, i.e. that BMI categorisation could have a degree of subjectivity, or be applied arbitrarily.

bmiThe WHO has recommended a standard classification, which, in brief, sorts body mass into six ranges:

  • Under-weight: 18.5 kg/h2 or less
  • Normal: 18.5–24.99 kg/h2
  • Over-weight: 25.00–29.99 kg/h2
  • Obese (class I): 30.00–34.99 kg/h2
  • Obese (class II): 35.00–39.99 kg/h2
  • Obese (class III) 40 kg/h2 or greater

However, some medical professionals and researchers, particularly surgeons, dispute and disregard these definitions, particularly in terms of the classes of obesity. In addition, a study comparing measurements of adiposity using BMI to a method objectively quantifying the actual percentage of body fat with X-ray technology found that the BMI method was inaccurate in assessing the body fat of approximately 30% of the 1,691 subjects. The discrepancy of adipose measurement between the use of BMI and X-rays was significant. A recent study involving 1322 subjects found that BMI of either below 27 kg/h2 and above 40 kg/h2 were associated with increased mortality.

However, when another variable (waist circumference) was accounted for in this analysis, the association between mortality and a BMI of 40 kg/h2 and higher was decreased. When a second factor, hip circumference, was introduced, the analysis was inconclusive. On the other hand, very high BMI (45 kg/h or more) was associated with increased mortality.

In addition, the popular link between increasing BMI and the risk of death may not hold true for all ethnicities; 'normal' to 'low' BMI (20 or less) was associated with increased mortality in a study of over 1.1 million Asian people. A study comparing the association between mortality risk and BMI in Caucasian and African Americans found that increased BMI was associated with an increased risk in Caucasians, but not in those of African descent.

One study, including over 85,000 Americans, found that increased BMI (in the obese, but not overweight, classes) was associated with the increased risk of cardiovascular disease. However, this study used measures of BMI supplied by the subjects themselves, which was not confirmed by any other measure of adiposity. In addition, self-reported BMI has been shown to be subject to inaccuracy and subjectivity, which can result in over- (or under-) estimation of the prevalence of obesity in epidemiological studies. It is interesting that BMI in the 'overweight' category is often not strongly associated with an increased risk of death or cardiovascular disease.

Waist circumference

Humans tend to store excess fat around the abdomen, which is particularly associated with the risk of cardiovascular disease. Therefore, measuring the length of the waist may be a better and more reliable measure of obesity than BMI.

When this is taken into account in studies assessing mortality risk, it may affect, and even confound, the association of BMI with this risk.

Greater waist circumference is associated with the increased risk of cardiovascular disease, and may be associated with increased mortality independent of an individuals BMI.

A study using the Health Survey for England data found that a ratio of waist-length to height was more effective in assessing life expectancy than BMI.

A review of 24 studies including over 512,000 subjects indicated that this ratio had a greater capacity to detect obesity, diabetes, the risk of cardiovascular disease and mortality risk in comparison with BMI.

Hip circumference

Hip circumference increases may also be a good indicator of adiposity, particularly in women, who also tend to store fat in this area. Rather counter-intuitively, higher hip circumference has been found to be associated with a decreased risk of cardiovascular disease and death. This may indicate that the comparison (or ratio) of waist and hip measurements is a good indicator of ill health in conjunction with high body fat.
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