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Waist to hip ratio is better as a predictor of heart attack than body mass index (BMI):
Does that mean we should abandon the BMI?
(March 2006)

In decades past, normal weight was determined from charts such as those of the Metropolitan Life Insurance Company. These determined normal weight from a combination of height and body build (small, medium, large frame). More recently, this way of determining normal weight was supplanted by the Body Mass Index - the weight in kilograms divided by the square of the height in meters. A BMI of 20 to 24.9 is normal weight, 25 to 29.9 overweight, 30 to 34.9 mild obesity, 35 to 39.9 moderate to marked obesity, and 40 and over severe obesity ( CLICK HERE to calculate your own BMI). The BMI has some problems. It ignores muscle and bone structure, so some heavily muscled people can have BMIs over 30 and not really be obese at all. Additionally, the BMI number does not take age into account when labeling people as overweight and obese. A BMI of 31 has a different significance in regard to health for a 70 year old compared to a 30 year old (very little significance versus a reason for some concern). Now, a multi-country group of investigators of the INTERHEART study argue that the BMI is not nearly as informative as the waist:hip ratio. They compared 12,461 cases of first heart attack with 14,637 controls from all major geographic areas of the world in regard to BMI, waist circumference, hip circumference, and waist:hip ratio, relating each of these to risk of heart attack. A waist hip ratio of greater than 1.0 is high for men; a ratio of greater than 0.95 is high for women (others use a lower ratio as the definition of high - 0.9 for men, 0.8 for women)..

The cases and controls were divided into five groups (quintiles) for each measurement. Body mass index was a predictor for heart attack; the top three quintiles in BMI had an approximately 30 to 44 percent increased risk of heart attack. However, this increased risk was accounted for by elevated blood pressure, smoking, diabetes, cholesterol elevation, and other variables; so the increased risk was not due to weight alone (everyone with a BMI over 30 was lumped into a single obesity category). In contrast, the waist:hip ratio was a much better predictor. Those in the two top waist:hip ratio quintiles had a 2 to 2.5 fold increased risk that remained highly significant even after taking into account smoking history, high blood pressure, the presence of diabetes, and other specific heart attack promoting risk factors. The waist:hip ratio was a good predictor for both men and women and for the various populations around the world.

Commentary: This is a very good study. The authors want to redefine obesity, abandoning the BMI, at least as a risk factor for heart attack. That would be carrying the results of the study too far. The following are relevant points.

- The concept of the dangers of the big gut are not new. It has long been emphasized that a big gut, that is a high waist:hip ratio is unhealthy and a major risk factor for cardiovascular disease, especially stroke.

- Recent evidence suggests that the dangers of obesity are found particularly for those whose BMI is 35 and over (at least moderate obesity, that is at least 40 percent over desirable weight). This study did not really focus on that point. A BMI of 35 and over is a significant risk factor for heart attack and stroke in those under age 70, acting in considerable part through obesity-related high blood pressure.

- The authors say that their waist:hip ratio predictive value applies to young and old, but it is hard to find a definition of those designations and the data presented do not tell us adequately the relation of high waist:hip ratio for various age groups, especially those ages 65 to 69, 70 to 79, and 80 and over.

- This is a case-control study. That is always an issue. The authors say they had more than one control per case and many of the controls appear to be hospitalized patients without heart attacks; some of these would likely have low waist:hip ratios because of their diseases. Hospital controls is always an issue. To be definitive, a study would have to be designed in which a large group had waist:hip ratios determined repeatedly and then were followed for a decade or longer to see who did and who did not develop heart attacks, strokes, and cancer.

- The results can be applied only to coronary heart disease and heart attacks though they will probably also apply to strokes; whether they will apply to cancers is unclear.

Yusuf, S., et al. Obesity and the risk of myocardial infarction in 27,000 participants from 52 countries. The Lancet. Vol 366 (November 5) Pgs 1640-1649. 2005.

The waist:hip ratio is informative; so is the BMI. For those determining their waist:hip ratio, it would probably be a good idea to have a health professional show you how to do it accurately. For those who want to keep it simple, weighing yourself regularly, checking your BMI, and seeing whether you are developing or have a big gut should give you the information you need to decide what actions you should take.

Remember, if your BMI is elevated (above 25), you should (really, you must) check your blood pressure, blood glucose (sugar), and cholesterol level. If you are overweight, keeping them in the normal range (especially the blood pressure) is, health wise, very important.

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