The researchers found that the well-documented association between obesity and increased CVD risk was actually the effect of the metabolic syndrome.

Dr Oscar Marroquin, from the department of epidemiology at the University of Pittsburgh in the US, explained: 'We wanted to see whether some of the risk associated with obesity was mediated through the metabolic syndrome rather than raised BMI itself.

'We found that obesity by itself, in the absence of the metabolic syndrome, does not predict CVD risk. It is only when you include the metabolic syndrome in the equation that you can predict CVD risk.'

The study included 788 women aged between 21 and 86 years, who had been referred for coronary angiography for suspected MI. The researchers measured the women's BMI and metabolic status of the women (see box) and then monitored them over three years, recording all major cardiovascular events.

They found that metabolic status was strongly related to BMI - 28 per cent of women with a normal BMI had the metabolic syndrome, compared to 55 per cent of overweight women and 76 per cent of those who were obese.

Women with the metabolic syndrome had a higher risk of death or a major adverse event. However, there was no increased risk among women who were obese but had no metabolic abnormality (Circulation 2004; 109: 706-13).

Dr Marroquin commented: 'The constellation of factors that are lumped in together as the metabolic syndrome are what actually predict CVD risk, not obesity.

'This makes sense because obesity, as measured by BMI, does not tell you anything about the metabolic state of the patient. These patients only do badly because they have metabolic problems.'

However, Dr Marroquin warned that obese patients without the metabolic syndrome should still take steps to reduce their risk of CVD.

He said: 'The fact that BMI does not predict events does not mean that people who are overweight without the metabolic syndrome should not make an effort to improve their overall health. These patients are likely to go on to develop metabolic abnormalities if they don't.

'All this research means is that when evaluating CVD risk, a measure of general obesity such as BMI is not as good an indicator as the metabolic syndrome,' Dr Marroquin concluded.

KEY CVD INDICATORS
Patients were diagnosed with the metabolic syndrome if they had three of
the following:
- Waist circumference more than 88cm
- Fasting triglycerides more than 150mg/dL
- HDL cholesterol less than 50mg/dL
- Systolic blood pressure gt/et 130mmHg; diastolic blood pressure gt/et
85mmHg
- Fasting glucose gt/et 110mg/dL