Two related news items caught my eye this morning:

First, the World Health Organization International Agency for Research on Cancer (IARC) has just published a new study in The Lancet claiming that in 2012, between 3% – 6% of all cancers around the world were attributable to high Body Mass Index (BMI), and that indications are that the trend is increasing (read the press release here).  The association was higher in economies with very high and high Human Development Indices (such as the US).  63.6% of the cancers associated with BMI globally were Corpus uteri, postmenopausal breast, and colon cancers, with women showing on average a higher rate of associated cancers.

The authors conclude

“These findings emphasise the need for a global effort to abate the increasing numbers of people with high BMI. Assuming that the association between high BMI and cancer is causal, the continuation of current patterns of population weight gain will lead to continuing increases in the future burden of cancer.”

The second item was a piece in Vox on the release of the Food and Drug Administration’s (FDA) new calorie label requirements for eating establishments.  According to the FDA,

“The menu labeling final rule applies to restaurants and similar retail food establishments if they are part of a chain of 20 or more locations, doing business under the same name and offering for sale substantially the same menu items. Covered food establishments will be required to clearly and conspicuously display calorie information for standard items on menus and menu boards, next to the name or price of the item. Seasonal menu items offered for sale as temporary menu items, daily specials and condiments for general use typically available on a counter or table are exempt from the labeling requirements.”

The new FDA rule is clearly focused on reducing obesity-related health issues.  With the new IARC study, it seems that cancer can be added to those issues.

Except that both the association between BMI and cancer, and the utility of calorie labels, are more nuanced than either of these news items might suggest.

The IARC study draws conclusions on the assumption of a causal relationship between BMI (a somewhat controversial  measure of obesity) and cancer.  While there is undoubtedly a causal relationship between high BMI and health complications that are also associated with cancer, I’m not convinced as to how strong the direct causal link is at this point, or the degree to which there is certainty that reducing BMI alone will reduce cancer risk significantly.

The labeling rule, while it makes sense intuitively, is not backed up by a whole lot of data.  There is certainly evidence that calorie labels don’t change eating behavior in some cases.  And there’s the counter concern that labels will encourage harmful eating behaviors in the millions of people suffering from eating disorders. Although on the positive side, calorie labels can be useful to individuals actively seeking to change eating habits, or maintain heathy eating behaviors.

At this point, it’s not clear that the new calorie labels will have a significant impact on cancer rates – or other obesity-related health issues.  That said, both news items highlight a growing need to understand the long term risks and benefits of eating habits, and the options available to reduce risks and increase health and well-being through what and how we eat.

Update 11/26/14 9:01 EST: it’s worth noting this quote on causality from the IARC study: “the estimation of the PAF is based on the assumption that the association between high BMI and each cancer type included in our study is causal.60 We thus assume that reducing BMI will lead to a reduction in the incidence of these cancers. Excess bodyweight has been shown to increase circulating levels of oestrogens and bioactivity of IGF-1, hence promoting the development of cancer. However, epidemiological studies that report risk associations between BMI and cancer are prone to several limitations. Residual confounding might account for the association between obesity and some types of cancer, and this possibility was not accounted for in our analysis. We have tried to overcome this issue by exclusively using risk estimates based on large meta-analyses that included only high quality
studies and, whenever possible, only cohort studies.”