In 2005 the authoritative Journal of the American Medical Association published the results of a study conducted by Katherine Flegal and colleagues at the respected Center for Disease Control (CDC).  This work is an analysis of data derived from the National Health and Nutrition Examination Survey (NHANES) conducted in the USA. It was started in the 1970s and has continued until the present day. Large numbers of people are involved. Participants report regularly to a centre where various measurements are taken by professional health workers to ensure that the quality of the data is absolutely first class. The normal BMI range has been taken as the benchmark and given a value of 1.00.

The results are shown in Table 1.

TABLE 1 CDC STUDY RELATIVE RISKS ALL-CAUSE MORTALITY

BMI 25-59 Years 60-69 Years >70 Years
<18.5 Underweight 1.38 2.30 1.69
18.5-25 Normal 1.00 1.00 1.00
25-30 Overweight 0.83 0.95 0.91
30-35 Obesity Class I 1.20 1.13 1.03
>35 Obesity Class II 1.83 1.63 1.17

 

These results show that risks of dying are slightly smaller in the ‘’Overweight’’ category than in the ‘’Normal’’ one.  The risks of those in ‘’Obese (Class I)’’ are only marginally increased, especially those aged over 70 years(1).

In Canada 11,326 men and women aged 25+ at the outset were monitored over a 12-year period commencing in 1994/1995 as part of the National Population Health Survey . The results are shown in Table 2.

These results provide confirmation of the Flegal study in the USA. It is evident that those in the “overweight” category have a much lower chance of dying and therefore a greater life expectancy than those in the “normal” range. However in this study, it was found that that those in the “Class1 obesity” also had a greater expectancy than those in the “normal range”(2).

TABLE 2 BMI AND MORTALITY IN CANADA

BMI <18.5 18.5-25 25-30 30-35 >35
All 1.51 1.0 0.75 0.84 1.09
Age 25-39 0.87 1.0 0.91 0.89 1.53
Age 60+ 1.88 1.0 0.81 0.96 1.25

So here we have 2 completely different investigations which both show that the lowest death rates are found in the “Overweight” category. Yet all the official publications in the UK and in many other countries are telling people who are overweight as determined by BMI that they have an increased risk of various diseases with the clear implication that it would be advisable to reduce their weight. Does it really make sense to try to achieve a weight loss that will result in a BMI with higher death rate than already applies??

Next time I will show how the risks of various diseases vary with BMI

REFERENCES

  1. K M Flegal et al (2005) Journal of the American Medical Association 293 (15) pp 1861-1867.
  2. Heather M Orpana et al(2010) Obesity18 (1) pp214-218.