
Weight loss and obesity have been in the news again, mostly due to new drugs being approved to treat obesity. Because of this, it’s a good opportunity to provide an update on obesity and breast cancer. A recent study came out focusing on women with BRCA mutations and how obesity affected their cancer risk. The study’s basic conclusion was that post-menopausal obesity increases the risk of breast cancer in people with a BRCA mutation. This information is not necessarily new, but there hasn’t been a lot of research on this population regarding obesity, so this study provides a more complete view of the risk.
One major bright spot in the study was that the researchers had the best explanation for the actual mechanism of how obesity can increase the risk of breast cancer, specifically for those who have a BRCA mutation. Essentially, obesity can lead to DNA damage in the breast cells due to increased estrogen levels from fat cells. BRCA genes, which everyone has, are DNA repair genes, so they get activated if the body notices an issue. BRCA genes that have a mutation are bad at their job, and a botched DNA repair can lead to breast cancer.
Think of it this way: you live in an apartment building with bad plumbing, so you keep having water issues. The property manager keeps sending the same “chewing gum and paper clips” maintenance worker to fix the issues. The more problems the building has with plumbing, the higher the likelihood that the worker without plumbing expertise will screw up big time. Similarly, the more DNA damage the BRCA genes have to repair, the greater the possibility of developing cancer.
Another positive about this study was that most of the obese subjects did not also have high blood pressure, diabetes, or high cholesterol, which could be confounding variables when looking at obesity. A “confounding variable” is something that can make the results of a study less clear and make it harder to see a clear relationship in the data. For example, a kindergarten teacher with an autoimmune disorder has a virus or bacterial infection every month. Is she frequently sick because her autoimmune disorder isn’t being well treated or because she is surrounded by kids who don’t wash their hands and cough in her face? Without the confounding variables of these other health conditions in this study, the relationship between obesity and DNA damage is cleaner and easier to connect.
Here’s the main problem with this study: BMI is used as the indicator for obesity. In our previous article, we explained how BMI is not a great tool when assessing body fat percentage or overall health because important factors like muscles are not considered in the calculation. A DEXA scan, which can separate out the weight of someone’s bones, muscles, and body fat, is a much more accurate way of measuring obesity. However, it is also more expensive and complicated, so research continues to rely on BMI.
Particularly when it comes to breast cancer, muscle composition may be an important factor in understanding how someone’s body processes insulin. Insulin sensitivity remains a little understood but hot topic in the understanding of breast cancer risk, and it is more complicated than whether someone has diabetes or not. A term that you may see come up in literature, including this study, is “metabolically obese,” meaning someone’s BMI is not in the obese range, but their insulin resistance is similar to that of a person with obesity. A question this brings up is if insulin resistance can appear in people who are obese/overweight and those who aren’t, why do we even bring weight into this conversation? If insulin resistance is the mechanism, then let’s focus on it rather than the number on the scale.
As far as the new weight loss drugs are concerned, it is far too soon to tell if losing weight using those drugs will have any effect on breast cancer risk. A lot of cancer studies require longitudinal data, meaning that the researchers follow subjects for a long time, preferably a decade or more. These medications haven’t been available long enough to a large enough number of people to get any kind of good data on cancer risk after taking the medications. Additionally, weight loss too quickly or at the wrong time could cause health issues of its own.
In short, the effect of weight or body fat on health remains more complicated than reading the numbers on the scale. What we can say is that if you are concerned about your weight and its effect on your health, please talk to your healthcare provider.