Causes and Correlates of Visceral ObesityDefining CMR - Visceral Adipose Tissue: the Culprit?
Obesity is an acknowledged health hazard and risk factor for cardiovascular disease (CVD) and type 2 diabetes, yet physicians have been perplexed by the remarkable heterogeneity of obese patients in clinical practice. Some obese patients display no CVD risk factors whereas others have type 2 diabetes, clinical signs of coronary heart disease, and are characterized by insulin resistance, atherogenic dyslipidemia, and a whole constellation of risk factors. Though we know that obesity is a health hazard, it is still unclear why this condition is so heterogeneous in its clinical manifestations.
The fact that obesity is so multifaceted means it must be redefined as a clinical entity. Evidence published over the last 25 years has proven that the subgroup of overweight or obese patients with excess abdominal fat—visceral fat in particular—has the highest risk of developing type 2 diabetes and CVD. Many factors influence the accumulation of visceral fat.
There is a definite sex difference in adipose tissue distribution:
- Men accumulate adipose tissue in the visceral cavity (apple pattern).
- Women accumulate adipose tissue in the gluteal/femoral depots (pear pattern).
- Visceral adipose tissue accumulation—the adipose tissue distribution pattern generally found in men—predicts greater obesity-related health risks.
- Pre-menopausal women have less visceral adipose tissue and a more favourable metabolic risk profile than men with similar total body fat. This protection against visceral fat accumulation is lost when women enter menopause.
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Influence of Age
- Visceral adiposity increases with age. This is particularly true for men when compared to pre-menopausal women.
- Visceral adipose tissue accumulation with age predicts greater obesity-related health risks.
- Visceral adipose tissue accumulation may partly explain the metabolic deteriorations observed with ageing.
- In clinical practice, a simple approach to identify individuals gaining visceral fat is to measure changes (increases) in waist circumference over time.
Read more on the Influence of Age.
Influence of Menopause
- Visceral adiposity increases with the onset of menopause.
- Abdominal tissue redistribution with menopause appears to be independent of age and total body fat and could be related to a relative deficit in estrogens.
- Menopause has a negative impact on plasma lipoprotein-lipid levels, which may increase CVD risk.
- HTR in post-menopausal women helps protect against visceral fat accumulation. However, prospective studies that have assessed “hard” CVD endpoints have failed to confirm HRT’s benefits.
- Current evidence does not support the use of HRT to reduce menopause-related CVD risk.
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Influence of Ethnicity
There are clear ethnic differences in BMI and adipose tissue distribution:
- Asian and Caucasian populations are more likely to accumulate adipose tissue in the visceral cavity than African Americans.
- Despite a higher BMI, black women are more likely to accumulate fat subcutaneously. Because they are less likely to develop visceral obesity, they may also be less prone than Caucasians to developing the high triglyceride-low-HDL cholesterol dyslipidemic state.
- Populations characterized by a large amount of visceral adipose tissue generally have a less favourable metabolic risk profile.
- Caucasian and Asian populations appear to accumulate more visceral adipose tissue and thus seem to be at highest risk of developing type 2 diabetes and CVD for a given BMI value.
Read more on the Influence of Ethnicity.