Abdominal Obesity
Complications Heart disease, asthma, stroke, diabetes
Causes Sedentary lifestyle, Overeating,
Cushing's syndrome, Alcoholism, Polycystic ovarian syndrome, Prader-Willi
syndrome
Abdominal obesity, also
known as central obesity and truncal obesity, is a condition when excessive
visceral fat around the stomach and abdomen has built up to the extent that it
is likely to have a negative impact on health. Abdominal obesity has been
strongly linked to cardiovascular disease, Alzheimer's disease, and other
metabolic and vascular diseases.
Visceral and central
abdominal fat and waist circumference show a strong association with type 2
diabetes.
Visceral fat, also known as
organ fat or intra-abdominal fat, is located inside the peritoneal cavity,
packed in between internal organs and torso, as opposed to subcutaneous fat,
which is found underneath the skin, and intramuscular fat, which is found
interspersed in skeletal muscle. Visceral fat is composed of several adipose
depots including mesenteric, epididymal white adipose tissue (EWAT), and
perirenal fat. An excess of adipose visceral fat is known as central obesity,
the "pot belly" or "beer belly" effect, in which the
abdomen protrudes excessively. This body type is also known as "apple shaped",
as opposed to "pear shaped" in which fat is deposited on the hips and
buttocks.
Researchers first started to
focus on abdominal obesity in the 1980s when they realized it had an important
connection to cardiovascular disease, diabetes, and dyslipidemia. Abdominal
obesity was more closely related with metabolic dysfunctions connected with
cardiovascular disease than was general obesity. In the late 1980s and early
1990s insightful and powerful imaging techniques were discovered that would
further help advance the understanding of the health risks associated with body
fat accumulation. Techniques such as computed tomography and magnetic resonance
imaging made it possible to categorize mass of adipose tissue located at the
abdominal level into intra-
Health risks
Heart disease
Abdominal obesity is
associated with a statistically higher risk of heart disease, hypertension,
insulin resistance, and type 2 diabetes (see below). With an increase in the waist to hip ratio and
overall waist circumference the risk of death increases as well. Metabolic syndrome is associated with
abdominal obesity, blood lipid disorders, inflammation, insulin resistance,
full-blown diabetes, and increased risk of developing cardiovascular disease.
It is now generally believed that intra-abdominal fat is the depot that conveys
the biggest health risk.
Recent studies have
concluded that total and regional body volume estimates correlate positively
and significantly with biomarkers of cardiovascular risk and BVI calculations
correlate significantly with all biomarkers of cardio-vascular risk.
Diabetes
There are numerous theories
as to the exact cause and mechanism in type 2 diabetes. Central obesity is
known to predispose individuals for insulin resistance. Abdominal fat is
especially active hormonally, secreting a group of hormones called adipokines
that may possibly impair glucose tolerance. But adiponectin, an
anti-inflammatory adipokine, which is found in lower concentration in obese and
diabetic individuals has shown to be beneficial and protective in type 2
diabetes mellitus.
Insulin resistance is a major feature of diabetes mellitus type 2, and central obesity is correlated with both insulin resistance and T2DM Increased adiposity (obesity) raises serum resistin levels, 7 which in turn directly correlate to insulin resistance. Studies have also confirmed a direct correlation between resistin levels and T2DM. And it is waistline adipose tissue (central obesity) which seems to be the foremost type of fat deposits contributing to rising levels of serum resistin. Conversely, serum resistin levels have been found to decline with decreased adiposity following medical treatment.
Asthma
Developing asthma due to
abdominal obesity is also a main concern. As a result of breathing at low lung
volume, the muscles are tighter and the airway is narrower. Obesity causes
decreased tidal volumes due to reduced in chest expansion that is caused both
by the weight on the chest itself and the effect of abdominal obesity on
flattening the diaphragms. It is commonly seen that people who are obese
breathe quickly and often, while inhaling small volumes of air.[32] People with
obesity are also more likely to be hospitalized for asthma. A study has stated
that 75% of patients treated for asthma in the emergency room were either
overweight or obese.
Alzheimer's disease
Based on studies, it is
evident that obesity has a strong association with vascular and metabolic
disease which could potentially be linked to Alzheimer's disease. Recent
studies have also shown an association between mid-life obesity and dementia,
but the relationship between later life obesity and dementia is less clear. A
study by Debette et al. (2010) examining over 700 adults found evidence to
suggest higher volumes of visceral fat, regardless of overall weight, were
associated with smaller brain volumes and increased risk of
dementia.[34][35][36] Alzheimer's disease and abdominal obesity has a strong
correlation and with metabolic factors added in, the risk of developing
Alzheimer's disease was even higher. Based on logistic regression analyses, it
was found that obesity was associated with an almost 10-fold increase risk of
Alzheimer's disease.
Other health risks
Central obesity can be a
feature of lipodystrophies, a group of diseases that is either inherited, or
due to secondary causes (often protease inhibitors, a group of medications
against AIDS). Central obesity is a symptom of Cushing's syndrome and is also
common in patients with polycystic ovary syndrome (PCOS). Central obesity is
associated with glucose intolerance and dyslipidemia. Once dyslipidemia becomes
a severe problem, an individual's abdominal cavity would generate elevated free
fatty acid flux to the liver. The effect of abdominal adiposity occurs not just
in those who are obese, but also affects people who are non-obese, and it also
contributes to insulin.
Ghroubi et al. (2007)
examined whether abdominal circumference is a more reliable indicator than BMI
of the presence of knee osteoarthritis in obese patients. They found that it
actually appears to be a factor linked with the presence of knee pain as well
as osteoarthritis in obese study subjects. Ghroubi et al. (2007) concluded that
a high abdominal circumference is associated with great functional
repercussion.
Causes
Diet
See also: Diet and obesity
The currently prevalent
belief is that the immediate cause of obesity is net energy imbalance—the
organism consumes more usable calories than it expends, wastes, or discards
through elimination. Some studies indicate that visceral adiposity, together
with lipid dysregulation and decreased insulin sensitivity, is related to the
excessive consumption of fructose. Some evidence shows that in regards to
juveniles, when free fructose is present as children's fat cells mature, it
makes more of these cells mature into fat cells in the abdominal region. It
also caused both visceral fat and subcutaneous fat to be less sensitive to
insulin. These effects were not attenuated when compared to similar glucose
consumption.[43]
Intake of trans fat from
industrial oils has been associated with increased abdominal obesity in men and
increased weight and waist circumference in women. These associations were not attenuated when
fat intake and calorie intake was accounted for. Greater meat (processed meat, red meat, and
poultry) consumption has also been positively associated with greater weight
gain, and specifically abdominal obesity, even when accounting for calories. Conversely, studies suggest that oily fish
consumption is negatively associated with total body fat and abdominal fat
distribution even when body mass remains constant.[50][51] Similarly, increased
soy protein consumption is correlated with lower amounts of abdominal fat in
postmenopausal women even when calorie consumption is controlled.
Numerous large studies have
demonstrated that eating ultraprocessed food. It has a positive dose-dependent
relationship with both abdominal obesity and general obesity in both men and
women. Consuming a diet rich in unprocessed food and minimally processed food
is linked with lower obesity risk, lower waist circumference and less chronic
disease. These findings are consistent among America Canadian, Latin American, British, Australian, French,
Spaniard South Korean. Chinese, and Sub-Saharan African populations.
Obesity plays an important
role in the impairment of lipid and carbohydrate metabolism shown in
high-carbohydrate diets. It has also
been shown that quality protein intake during a 24-hour period and the number
of times the essential amino acid threshold of approximately 10 g has been
achieved is inversely related to the percentage of central abdominal fat.
Quality protein uptake is defined as the ratio of essential amino acids to
daily dietary protein.
Visceral fat cells will
release their metabolic by-products in the portal circulation, where the blood
leads straight to the liver. Thus, the excess of triglycerides and fatty acids
created by the visceral fat cells will go into the liver and accumulate there.
In the liver, most of it will be stored as fat. This concept is known as
'lipotoxicity'.
Alcohol consumption
A study has shown that
alcohol consumption is directly associated with waist circumference and with a
higher risk of abdominal obesity in men, but not in women. After controlling
for energy under-reporting, which have slightly attenuated these associations,
it was observed that increasing alcohol consumption significantly increased the
risk of exceeding recommended energy intakes in male participants – but not in
the small number of female participants (2.13%) with elevated alcohol consumption,
even after establishing a lower number of drinks per day to characterize women
as consuming a high quantity of alcohol. Further research is needed to
determine whether a significant relationship between alcohol consumption and
abdominal obesity exists among women who consume higher amounts of alcohol.
A systemic review and
meta-analysis failed to find data pointing towards a dose-dependent
relationship between beer intake and general obesity or abdominal obesity at
low or moderate intake levels (under ~500 mL/day). However, high beer intake
(above ~4 L/wk) appeared to be associated with a higher degree of abdominal
obesity specifically, particularly among men.
Other factors
The prevalence of abdominal
obesity is increasing in Western populations, possibly due to a combination of
low physical activity and high-calorie diets, and also in developing countries,
where it is associated with the urbanization of populations.
Other environmental factors,
such as maternal smoking, estrogenic compounds in the diet, and
endocrine-disrupting chemicals may be important also.
Hypercortisolism, such as in
Cushing's syndrome, also leads to central obesity. Many prescription drugs,
such as dexamethasone and other steroids, can also have side effects resulting
in central obesity,[37] especially in the presence of elevated insulin levels.
Diagnosis
There are various ways of
measuring abdominal obesity including:
Absolute waist circumference
(>102 cm (40 in) in men and >88 cm (35 in) in women.
Overweight teenage
boy holding his excess abdominal fat
In those with a body mass
index (BMI) under 35, intra-abdominal body fat is related to negative health
outcomes independent of total body fat.[76] Intra-abdominal or visceral fat has
a particularly strong correlation with cardiovascular disease.
BMI and waist measurements
are well recognized ways to characterize obesity. However, waist measurements
are not as accurate as BMI measurements. Waist measurement (e.g., for BFP
standard) is more prone to errors than measuring height and weight (e.g., for
BMI standard). BMI will illustrate the best estimate of one's total body
fatness, while waist measurement gives an estimate of visceral fat and risk of
obesity-related disease. It is
recommended to use both methods of measurements.
An adult man with
abdominal obesity
While central obesity can be
obvious just by looking at the naked body (see the picture), the severity of
central obesity is determined by taking waist and hip measurements. The
absolute waist circumference 102 centimetres (40 in) in men and 88 centimetres
(35 in) in women and the waist–hip ratio (>0.9 for men and >0.85 for
women are both used as measures of central obesity. A differential diagnosis
includes distinguishing central obesity from ascites and intestinal bloating.
In the cohort of 15,000 people participating in the National Health and
Nutrition Examination Survey (NHANES III), waist circumference explained
obesity-related health risk better than BMI when metabolic syndrome was taken
as an outcome measure and this difference was statistically significant. In
other words, excessive waist circumference appears to be more of a risk factor
for metabolic syndrome than BMI. Another measure of central obesity which has
shown superiority to BMI in predicting cardiovascular disease risk is the Index
of Central Obesity (waist-to-height ratio, WHtR), where a ratio of >=0.5
(i.e. a waist circumference at least half of the individual's height) is
predictive of increased risk. Obesity
may also be diagnosed through the
analysis of intra-abdominal fat having the most risk to one's personal health.
The increased amount of fat in this region relates to the higher levels of
plasma lipid and lipoproteins as per studies mentioned by Eric Poehlman (1998)
review. An increasing acceptance of the importance of central obesity within
the medical profession as an indicator of health risk has led to new
developments in obesity diagnosis such as the Body Volume Index, which measures
central obesity by measuring a person's body shape and their weight
distribution. The effect of abdominal adiposity occurs not just in those who
are obese, but also affects people who are non-obese and it also contributes to
insulin sensitivity.
Index of central
obesity
Index of Central Obesity
(ICO) is the ratio of waist circumference and height first proposed by Parikh
et al. in 2007[81] as a better substitute to the widely used waist
circumference in defining metabolic syndrome. The National Cholesterol Education Program
Adult Treatment Panel III suggested cutoff of 102 cm (40 in) and 88 cm (35 in)
for males and females as a marker of central obesity.The same was used in
defining metabolic syndrome. Misra et al. suggested that these cutoffs are not
applicable among Indians and the cutoffs be lowered to 90 cm (35 in) and 80 cm
(31 in) for males and females. Various race specific cutoffs were suggested by
different groups. The International Diabetes Federation defined central obesity
based on these various race and gender specific cutoffs. The other limitation
of waist circumference is that it the measurement procedure has not been
standardized and in children there are no, or few, comparison standards or
reference data.
Parikh et al. looked at the
average heights of various races and suggested that by using ICO various race-
and gender-specific cutoffs of waist circumference can be discarded.[82] An ICO
cutoff of 0.53 was suggested as a criterion to define central obesity. Parikh
et al. further tested a modified definition of metabolic syndrome in which
waist circumference was replaced with ICO in the National Health and Nutrition
Examination Survey (NHANES) database and found the modified definition to be
more specific and sensitive.
This parameter has been used
in the study of metabolic syndrome and cardiovascular disease.
Central obesity in
individuals with normal BMI is referred to as normal weight obesity.
Sex differences
There are sex-dependent
differences in regional fat distribution.
Males are more susceptible
to upper-body fat accumulation, most likely in the belly, due to sex hormone
differences. When comparing the body fat of men and women it is seen that men
have close to twice the visceral fat as that of pre-menopausal women.
In women, estrogen is
believed to cause fat to be stored in the buttocks, thighs, and hips. When
women reach menopause and the estrogen produced by ovaries declines, fat
migrates from their buttocks, hips, and thighs to their belly.
50% of men and 70% of women
in the United States between the ages of 50 and 79 years now exceed the waist
circumference threshold for central obesity.
Central obesity is
positively associated with coronary heart disease risk in women and men. It has
been hypothesized that the sex differences in fat distribution may explain the
sex difference in coronary heart disease risk. Even with the differences, at
any given level of central obesity measured as waist circumference or waist to
hip ratio, coronary artery disease rates are identical in men and women.
Management
A permanent routine of
exercise, eating healthily, and, during periods of being overweight, consuming
the same number or fewer calories than used will prevent and help fight
obesity. A single pound of fat yields approximately 3500 calories of energy (32
000 kJ energy per kilogram of fat), and weight loss is achieved by reducing
energy intake, or increasing energy expenditure, thus achieving a negative
balance. Adjunctive therapies which may be prescribed by a physician are
orlistat or sibutramine, although the latter has been associated with increased
cardiovascular events and strokes and has been withdrawn from the market in the
US, the UK, the EU, Australia,[105] Canada, Hong Kong] and Thailand.[
A 2006 study published in
the International Journal of Sport Nutrition and Exercise Metabolism, suggests
that combining cardiovascular (aerobic) exercise with resistance training is
more effective than cardiovascular training alone in getting rid of abdominal
fat. An additional benefit to exercising is that it reduces stress and insulin
levels, which reduce the presence of cortisol, a hormone that leads to more
belly fat deposits and leptin resistance.
Self-motivation by
understanding the risks associated with abdominal obesity is widely regarded as
being far more important than worries about cosmetics. In addition,
understanding the health issues linked with abdominal obesity can help in the
self-motivation process of losing the abdominal fat. As mentioned above,
abdominal fat is linked with cardiovascular disease, diabetes, and cancer.
Specifically it's the deepest layer of belly fat (the fat that cannot be seen
or grabbed) that poses health risks, as these "visceral" fat cells
produce hormones that can affect health (e.g. increased insulin resistance
and/or breast cancer risk). The risk increases considering the fact that they
are located in the proximity or in between organs in the abdominal cavity. For
example, fat next to the liver drains into it, causing a fatty liver, which is
a risk factor for insulin resistance, setting the stage for type 2 diabetes.
However, visceral fat is more responsive to the circulation of catecholamines.
In the presence of type 2
diabetes, the physician might instead prescribe metformin and
thiazolidinediones (rosiglitazone or pioglitazone) as antidiabetic drugs rather
than sulfonylurea derivatives. Thiazolidinediones may cause slight weight gain
but decrease "pathologic" abdominal fat (visceral fat), and therefore
may be prescribed for diabetics with central obesity. Thiazolidinedione has
been associated with heart failure and increased cardiovascular risk; so it has
been withdrawn from the market in Europe by EMA in 2010.
Low-fat diets may not be an
effective long-term intervention for obesity: as Bacon and Aphramor wrote,
"The majority of individuals regain virtually all of the weight that was
lost during treatment."[113] The Women's Health Initiative ("the
largest and longest randomized, controlled dietary intervention clinical
trial" found that long-term dietary intervention increased the waist
circumference of both the intervention group and the control group, though the
increase was smaller for the intervention group. The conclusion was that mean
weight decreased significantly in the intervention group from baseline to year
1 by 2.2 kg (P<.001) and was 2.2 kg less than the control group change from
baseline at year 1. This difference from baseline between control and
intervention groups diminished over time, but a significant difference in
weight was maintained through year 9, the end of the study.
Society and culture
Myths
There is a common
misconception that spot exercise (that is, exercising a specific muscle or
location of the body) most effectively burns fat at the desired location, but
this is not the case. Spot exercise is beneficial for building specific
muscles, but it has little effect, if any, on fat in that area of the body, or
on the body's distribution of body fat. The same logic applies to sit-ups and
belly fat. Sit-ups, crunches and other abdominal exercises are useful in
building the abdominal muscles, but they have little effect, if any, on the
adipose tissue located there.
Colloquialisms
A large central adiposity
deposit has been assigned many common use names, including "spare
tire", "paunch", and "potbelly". Several colloquial
terms used to refer to central obesity, and to people who have it, refer to
beer drinking. However, there is little scientific evidence that beer drinkers
are more prone to central obesity, despite its being known colloquially as
"beer belly", "beer gut", or "beer pot". One of
the few studies conducted on the subject did not find that beer drinkers are
more prone to central obesity than nondrinkers or drinkers of wine or spirits. Chronic alcoholism can lead to cirrhosis,
symptoms of which include gynecomastia (enlarged breasts) and ascites
(abdominal fluid). These symptoms can suggest the appearance of central
obesity.
Deposits of excess fat at
the sides of one's waistline or obliques are commonly referred to as "love
handles".
Economics
Researchers in Copenhagen
examined the relationship between waist circumferences and costs among 31,840
subjects aged 50–64 years of age with different waist circumferences. Their
study showed that an increase in just an additional centimetre above normal
waistline caused a 1.25% and 2.08% rise in health care costs in women and men
respectively. To put this in perspective, a woman with a waistline of 95 cm
(approx 37.4 in) and without underlying health problems or co-morbidities can
incur economic costs that are 22%, or US$397, higher per year than a woman with
a normal waist circumference.
Jan Ricks Jennings, MHA,
LFACHE
Senior Consultant
Senior Management
Resources, LLC
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September 24. 2022