Recently, a report published by the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) made a number of recommendations designed to ward off cancer, the most trumpeted of which is the need to maintain a ‘healthy’ weight. Specifically, we are encouraged to keep our body mass index (BMI) between 21-23 (the traditional ‘healthy’ BMI range extends from 18.5 to less than 25). This week, here in the UK we had a home-grown story with the same line: a study published in the British Medical Journal warns that excess weight will cause around 6,000 British women to develop cancer every year. The underlying message of recent times is that carrying ‘extra’ weight is a serious hazard to our health. But is it?
Last Friday, my blog highlighted the evidence showing that individuals traditionally regarded as ‘overweight’ enjoy health that is at least as good, if not better, than those who fall in the ‘healthy’ BMI category. One study I chose to mention specifically was one published in 2005 in the Journal of American Medical Association (JAMA) which found that overall risk of death was lower in ‘overweight’ individuals than individuals of ‘healthy’ weight . One commenter (Esther)was worried about my: tendency to seep [I think she meant sweep] away many studies that show one result, and offer one that disagrees.� I am genuinely happy to review my stance on things – in the light of good evidence. So I’ve asked Esther for the ‘many studies’ she refers to. Let’s see what turns up�.
In the meantime, I want to share with you research published this week on the same theme. The 2005 JAMA study’s lead author was Katherine Flegal, a scientist at the National Center for Health Statistics and the Centers for Disease Control and Prevention in Hyattsville, Maryland, USA. This week, Katherine Flegal has had published a more detailed analysis of the data on BMI and death. In this newest study, again published in the JAMA, Dr Flegal and her colleagues have drilled down to look at the relationship between BMI and not just death, but different causes of death. In particular, they divided causes of death into 3 categories: cardiovascular disease (CVD) deaths (e.g. heart attacks and strokes); cancer death; and non-CVD/non-cancer deaths.
Here’s what they found:
People in the ‘overweight’ category were not found to be at increased risk of death due to CVD or cancer.
Individuals in the ‘overweight’ category were not even found to be at increased risk of death from forms of cancer traditionally thought of as obesity-related (e.g. cancers of the breast, colon, ovary and womb).
Risk of death due to non-CVD/non-cancer causes was lowest for those in the ‘overweight ‘category, and this was ‘statistically significant’.
Again, overall risk of death was found to be lowest in individuals in the ‘overweight’ category, and this was ‘statistically significant’.
Individuals in the ‘obese’ category (BMI 30 and above) was associated with an increased risk of death overall, and this appeared to be due to an increased risk of CVD.
Individuals in the ‘obese’ category were not at significantly increased risk of death from cancer or non-CVD/non-cancer conditions.
So, could fat be the new fit?
Well, one thing is for sure: being ‘overweight’ according to the BMI scale does not mean someone is ‘fat’. That ‘additional’ weight may be, after all, the result of muscle, bone or whatever. And even if there is a bit of ‘padding’ present around the body, is this necessarily a bad thing? It might be a sign of greater ‘nutritional reserve’ which can be drawn on in times of need. Which, by the way, may reflect an evolutionary adaptation that has helped to ensure survival during times when food supply was limited. While starvation is less of an issue for the population analysed in the recent JAMA study, what may be relevant is that individuals of higher weight have been found to be at reduced risk of death in certain circumstances including critical illness and surgery.
Whatever the explanation, I believe there is now abundant evidence which shows that the conventional advice given to individuals around maintaining or attaining a ‘healthy’ BMI is simply not justified. So, until it seems we have good evidence to the contrary, my suggestion that we do not urge people to strive to conform to a body weight that may be quite unattainable and perhaps even detrimental to their health.
2. Reeves KR, et al. Cancer incidence and mortality in relation to body mass index in the Million Women Study: cohort study. BMJ doi:10.1136/bmj.39367.495995.AE (published 6 November 2007)
3. Flegal KM, et al. Excess deaths associated with underweight, overweight, and obesity. JAMA. 2005;20;293(15):1861-7
4. Flegal KM, et al. Cause-Specific Excess Deaths Associated With Underweight, Overweight, and Obesity. JAMA. 2007;298(17):2028-2037