I’ll send a personal message next week when I finish seeing patients and close my practice. This week I want to write (albeit late) my usual medical newsletter on a subject that I’ve covered many times: cancer risk from obesity. That risk has just been re-iterated in a special report published in the New England Journal of Medicine.
In the past, there was definitive data that showed that avoidance of weight gain improved the risk for cancers of the colon, esophagus, kidney, postmenopausal breast cancer and uterine cancer. In April of this year, the International Agency for Research on Cancer (IARC) convened a working group in Lyon, France to reassess the preventive effects of weight control on cancer risk. (I hope that the diet of this group did not include huge amounts of pomme frites and baguettes.) They reviewed more than 1,000 epidemiological studies on cancer risk associated with excess body fatness. They compared the risk to individuals who had a BMI of 18.5 to 24.9. Overweight is considered 25.0-29.9. Obesity is anything higher but can be divided into three classes.
Class 1 is 30.0-34.9.
Class 2 is 35.0-39.9.
Class 3 is equal to or greater than 40.0
Most of us know what BMI stands for but if you want to take out your calculators it is the weight in kilograms divided by the square of height in meters. It’s felt to be a good proxy for assessing overall body fatness.
Upon looking at all of the studies, the IARC came up with eight cancers for which they feel there is now sufficient evidence that the absence of body fatness lowers cancer risk. Here is a list of the cancers with the relative risk (RR) for the highest BMI category versus normal BMI.
Esophagus adenocarcinoma – RR 4.8
Stomach cancer – RR 1.8
Colon and rectal cancer – RR 1.3
Liver cancer – RR 1.8
Gallbladder cancer – RR 1.3
Pancreatic cancer – RR 1.5
Breast cancer, postmenopausal – RR 1.1
Uterine cancer – RR 7.1
Ovarian cancer – RR 1.1
Kidney cancer, renal-cell – RR1.8
Meningioma – RR 1.5
Thyroid cancer – RR 1.1
Multiple myeloma – RR 1.5
Obesity is associated with both metabolic and endocrine abnormalities which include alterations in the metabolism of sex hormones, insulin and insulin like growth factor as well as inflammatory pathways. The beneficial effects on cancer risk of low weight or weight loss may be due to regulation of these factors and ultimately the balance between cell multiplication and proliferation and cell death.
The conclusion of the IARC was that “On the basis of the available data, the absence of excess body fatness lowers the risk of most cancers. In addition, a review of studies in experimental animals and mechanistic data suggest a causal cancer-preventative effect of intentional weight loss.”
This sums up one of the major reasons that over all these years I have virtually hounded my patients and readers who are obese to lose weight with appropriate diet and exercise.