From Gerry Shaper
London
In Robert Pool’s report on new drugs for combating the epidemic of obesity in
the Western world
(“Things can only get thinner”, 23 August, p 22) there is a
box entitled “Can you be too skinny?” Here it states that for body mass indexes
(BMIs) up to 27 or 28, weight is not closely related to mortality, but that
above BMIs of 28 or 30, “extra fat increases blood pressure and cholesterol
levels, makes a heart attack more likely and, by triggering diabetes, can lead
to kidney failure”.
While this may be very comforting to the population at large, which has an
average BMI of about 26, several studies have shown that mortality is an
inadequate measure of the consequences of being overweight or obese. Instead,
research shows that healthy body weights may be better determined by using
criteria based on risk factors and morbidity (illness).
The British Regional Health Study followed almost 8000 middle-aged men drawn
from general practices in 24 British towns. It shows that men with BMIs between
22 and 24 have the lowest risk of experiencing heart attack, stroke, diabetes or
death from any cause. Levels of a wide range of risk factors for cardiovascular
disease, including blood pressure and blood cholesterol, rose progressively from
BMIs below 20.
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The study has previously explored the J-shaped relationship between BMI and
mortality and shown that the excess deaths in the very lean men is largely due
to cancer and other smoking-related diseases. In men who had never smoked the
lowest mortality was observed in those with a BMI of 20 to 22.
Clearly, even within the “normal” range of BMI (20 to 28) it is better to be
leaner, and the optimal healthy body mass index for adults appears to be about
22. As the proportion of the population with BMIs over 30 has doubled in the
past decade, the implications of these findings for public health are
considerable.
