Despite all the emphasis on BMI as an indicator of health status/risk of dying the fact remains that for any given body weight/BMI there is a wide variation in health because many others factors can come into play.

A recent study conducted in the USA has analysed the impact of various demographic and behaviour-related factors likely to affect all-cause mortality. 3,617 men and women were monitored between 1986 and 2005 during which time there were 1,409 deaths. The results confirmed earlier findings that low income is a predictor of mortality when allowance is made for major health risk behaviour. By contrast, physical activity – even at relatively low levels – provided a protective effect against mortality. Those with little or no physical activity had a 60% higher mortality rate than those who were reasonably active. The risk of death was not associated with obesity or overweight. For those over 55 at the start of the investigation, mortality rates were significantly reduced for those who were overweight or obese(1).

The levels of physical fitness for different BMI values were compared in 2603 men and women aged 60 years and over. 450 deaths were recorded over the 12-year follow-up period. The participants who died were older, less fit and had higher cardiovascular risks than those who survived.  The results in Table 1 show that there is very little difference in the death rates across the entire BMI range for those who were physically fit. However for those who were physically unfit, the death rates for those in the overweight and Class 1 obesity BMI categories were approximately twice as high as those who were fit. The death rates for those with BMIs in the normal and Class2 obesity ranges were even higher. Similar differences were also observed when obesity was assessed by waist circumference or by percent body fat(2).

TABLE 1

EFFECT OF PHYSICAL FITNESS ON DEATH RATES (PER/1000 PERSON-YEARS) FOR DIFFERENT BMI CATEGORIES

BMI FIT UNFIT
18.5-24.9 1.2 4.9
25.0-29.9 1.2 2.7
30.0-34.9 1.6 2.5
>35.0 1.2 4.8

 

Similarly Lee and co-workers observed that the higher risk of cardiovascular mortality was no longer significant once fitness change was taken into account. They also reported that all-cause mortality was not significantly associated with change in BMI(3).

In patients who had coronary heart disease and were also hypertensive it has been found that those who are overweight and obese had a much lower death rate compared with those in the “normal” BMI range. This study had 22,576 participants (61,835 patient-years) with an average age of 66 years. The authors concluded that the “excess” weight was actually protective(Table 2)(4).

TABLE 2.

HYPERTENSIVE PATIENTS WITH CORONARY HEART DISEASE

BMI Death Rate, hazard ratio%
<20 185
20-25 100
25-30  66
30-35  52
>35  50

 

A policy analyst, Jerome Gronniger, of the Congressional Budget Office in Washington DC reviewed the research on BMI and mortality and concluded that:

Normal weight individuals of both genders did not appear to be relatively more long-lived than mildly obese individuals (BMIs of 30-35) whereas overweight people (BMIs of25-30) appeared healthiest of all”(5).

Paul Campos is a Professor of Law at the University of Colorado who has made an extensive study of the research on overweight and obesity. He has concluded that most epidemiological studies on the relationship between body weight and mortality do not control for fitness, diet quality, weight cycling, diet drug use, economic status or family history. When one or more of these factors is controlled in a rigorous fashion the already weak association between increased mortality and higher body weight is usually eliminated(6).

The inevitable conclusion is that weight per se is not a critical factor which is related in any way to poor health except at the extremes. However we need to be just as concerned about those who are underweight as well as about those who are seriously obese. In the light of the information presented above, there can be absolutely no justification for recommending that those who fall into the “overweight” category should attempt to lose weight. In fact on this evidence it may well be ill-advised. There is also little evidence of ill-health with people who are in the Class 1 obese category. This applies especially to those who are aged 60 years or more, which is when the majority of deaths occur.

It is extremely difficult to understand why the Government and the public health authorities continue to advocate that such a high proportion of the population should be advised to lose weight.

 

REFERENCES

  1. Paula M Lantz et al. Social Science Medicine(2010) 70 (10) pp1558-1566.
  2. Xuemei Sui et al (2007) Journal of the American Medical Association 298 (21) pp 2507-2516.
  3. D Lee et al (2011) Circulation 124 (23) pp 2483-2490.
  4. S Uretsky The American Journal of Medicine (2007) 120 (10) pp 863-870.
  5. J Gronniger (2006) American Journal of Public Health 96 (1) pp 173-178)
  6. Paul Campos et al. (2006) International Journal of Epidemiology 35 (1) pp. 55-60.