Obesity Not Always Linked To Higher Cardiovascular Risk

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Main Category: Obesity / Weight Loss / Fitness
Also Included In: Cardiovascular / Cardiology
Article Date: 12 Aug 2008 - 9:00 PDT

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Two studies, one from Germany and another from the US published this week, suggest that obese people do not always carry an increased risk of heart disease, while some individuals of normal weight do. The clue appeared to lie in how body fat was distributed, for example fat in the abdomen, as indicated by a larger waist circumference, was a consistent risk factor in both studies.

Both studies, and an accompanying editorial, appear in the 11/25 August 2008 online issue of the Archives of Internal Medicine.

Obesity is increasing all over the world and is invariably accompanied by an increase in type 2 diabetes and cardiovascular disease. Numerous studies have suggested that as well as overall obesity, the way fat is distributed around the body may also be important in determining risk for heart disease and diabetes.

For example, people who have fat inside the abdominal cavity (waist size is a good indicator of this) seem to be more likely to develop insulin resistance and to have a higher risk of cardiovascular disease. Insulin resistance, a recognized symptom or precursor of diabetes, is where the body loses its ability to use insulin to control blood sugar.

The first paper describes how researchers at the University of Tübingen in Germany studied 314 people aged 18 to 69 (the average age was 45) by measuring their total body fat, their visceral fat (the fat around the abdomen and internal organs), and subcutaneous fat (fat under the skin) with magnetic resonance tomography. The participants also underwent an oral glucose tolerance test to measure their insulin resistance.

To do the analysis, first author Dr Norbert Stefan and colleagues arranged the subjects by weight into four groups: (1) normal weight, (2) overweight, (3) obese with insulin sensitivity (ie no resistance) and (4) obese with insulin resistance.

The results showed that:

• Overweight and obese individuals had more visceral and total body fat than the normal weight individuals.


• Obese individuals with insulin resistance had more fat in skeletal muscles and the liver than obese individuals who were insulin sensitive.


• The insulin resistant individuals had thicker walls in their carotid arteries, which is an early indicator of narrowing of the arteries or atherosclerosis, a risk factor for heart disease.


• The obese insulin sensitive individuals had the same level of insulin sensitivity and artery wall thickness as the normal weight group.

Stefan and colleagues concluded that:

"We provide evidence that a metabolically benign obesity can be identified and that it may protect from insulin resistance and atherosclerosis."

They also wrote that:

"Our data suggest that ectopic [misplaced] fat accumulation in the liver may be more important than visceral fat in the determination of such a beneficial phenotype in obesity."

In the second study, researchers at the Albert Einstein College of Medicine in the Bronx, New York, studied body weight and indices of cardiometabolic abnormality in 5,440 people who took part in the National Health and Nutritional Examination Surveys (NHNES) between 1999 and 2004.

First author Dr Rachel P Wildman and colleagues classed participants as metabolically healthy if they had none or one cardiometabolic abnormality, and classed them as metabolically abnormal if they had two or more. Examples of cardiometabolic abnormality included high blood pressure, a high level of triglycerides and a low level of "good" HDL cholesterol.

Extrapolating the results to the population at large, the authors found that among US adults aged 20 and above:

• 23.5 per cent (about 16.3 million) of those at normal weight were metabolically abnormal.


• 51.3 per cent (about 35.9 million) of those who were overweight, and 31.7 per cent (about 19.5 million) of those who were obese were metabolically healthy.


• Normal weight people who were metabolically abnormal tended to be older, less physically active and had larger waists than normal weight individuals who were metabolically normal.


• Obese people who were metabolically normal tended to be younger, black, more physically active and had smaller waists than their metabolically abnormal counterparts.

Wildman and colleagues concluded that:

"These data show that a considerable proportion of overweight and obese US adults are metabolically healthy, whereas a considerable proportion of normal-weight adults express a clustering of cardiometabolic abnormalities."

They said further studies should be done to find the underlying behavioural, genetic, hormonal and biochemical mechanisms that might explain these results and help develop better screening tools and weight-loss treatments for cardiovascular diseases.

In an accompanying editorial, Dr Lewis Landsberg from the Northwestern University Comprehensive Center on Obesity based in Chicago, said that both studies found that body fat outside of the abdomen was not as closely linked to cardiovascular disease risk as visceral fat, and its "surrogate", waist circumference. They in fact confirm other studies that link waist circumference, even in normal weight people, to higher cardiovascular risk.

The studies help to improve the understanding of obesity and how it should be used to predict which patients are likely to develop cardiovascular disease, wrote Landsberg, who suggested clinicians should use body mass index and waist circumference to assess cardiovascular risk.

"Identification and Characterization of Metabolically Benign Obesity in Humans."
Norbert Stefan; Konstantinos Kantartzis; Jurgen Machann; Fritz Schick; Claus Thamer; Kilian Rittig; Bernd Balletshofer; Fausto Machicao; Andreas Fritsche; Hans-Ulrich Haring.
Arch Intern Med. 2008;168(15):1609-1616.

Click here for Abstract.

"The Obese Without Cardiometabolic Risk Factor Clustering and the Normal Weight With Cardiometabolic Risk Factor Clustering: Prevalence and Correlates of 2 Phenotypes Among the US Population (NHANES 1999-2004)."
Rachel P. Wildman; Paul Muntner; Kristi Reynolds; Aileen P. McGinn; Swapnil Rajpathak; Judith Wylie-Rosett; MaryFran R. Sowers
Arch Intern Med. 2008;168(15):1617-1624.

Click here for Abstract.

"Body Fat Distribution and Cardiovascular Risk: A Tale of 2 Sites."
Lewis Landsberg
Arch Intern Med. 2008;168(15):1607-1608.

Click here for Abstract.

Sources: Journal Abstracts, JAMA press release.

Written by: Catharine Paddock, PhD
Copyright: Medical News Today
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