Joy Victory is Deputy Managing Editor of HealthNewsReview.org. She tweets at @thejoyvictory.
An extremely brief New York Times “Well” post published last week — “A ‘Sweet Spot’ for Heart Health” — suggests that people must be within a very narrow weight range–a body-mass index (BMI) of 21 to 23–if they want to reduce their risk of heart disease as much as possible.
The Times’ article reports on a prospective study of nearly 300,000 middle-aged British men and women, followed for about five years, who had their relative body fat measured by five methods: body-mass index (BMI), waist circumference, waist-to-hip ratio, waist-to-height ratio, and body fat percentage.
The British study adds to a growing body of research that shows that the so-called “obesity paradox” — the notion that a slightly higher than “normal” BMI may reduce mortality — may not really exist. Such was the case with this study: Increasing BMI was associated with an increased risk for heart disease, as well as with the other measurements for measuring body fat.
And there was no BMI “sweet spot,” so to speak. Overall–after researchers controlled for things like smoking and coexisting health conditions–the less people weighed, the less likely they were to develop heart disease.
But the Times’ article doesn’t provide this context and instead implies that people must be within a narrow BMI range–not too low, and not too high. It also doesn’t explain that the BMI is an imperfect tool and shouldn’t be used in isolation: Very fit athletes, for example, can have a high BMI that places them in the “overweight” category.
Nor is it mentioned that this kind of research, known as a prospective cohort study, is not designed to prove that obesity — or even fat itself — causes cardiovascular disease. All the variables that likely contribute to heart disease cannot be fully accounted for in this kind of study design.
Of course, there is extensive evidence that obesity is associated with numerous health risks including cardiovascular disease. But whether there’s really such a thing as a narrow “sweet spot” cannot be conclusively determined by this type of study, and the article should have said as much.
As one reader noted: “Once again we are treated to a correlations=causation conclusion that is not actually made by the study. It may be that meeting a target BMI will reduce your chances of having cardiovascular disease or it may be an irrelevant marker of the real causes.”