Today’s topic is a guest post by a fellow oncology dietitian who also helped me write my handout on sugar and cancer. I feel like we go “way back” even though I think we’ve only met once in real life! I very much appreciated her perspective and asked if I could share on the blog. She agreed! I hope you find benefit too.
I’m working on getting my latest survivorship cooking class recipes up here soon, so stay tuned for some delicious Mediterranean inspired ideas to use in your home cooking!
Should cancer survivors avoid dairy?
By Angelea Bruce, RD, CSO, OPN-CG
Last week, the International Journal of Epidemiology published a study that concluded that drinking dairy milk is associated with a greater risk for breast cancer.
The researchers reported that drinking as little as a third of a cup of milk a day appeared to increase breast cancer occurrence by about 30%. Eating cheese or yogurt did not appear to have any effect.
As an oncology dietitian who will inevitably be asked about this by understandably worried women, I decided to take a closer look at the study and its findings.
As the journal title suggests, the researchers used a type of study design called an observational study. This type of study can describe and potentially identify a correlation between two or more variables, like milk intake and rates of breast cancer occurrence.
It cannot, however, identify cause and effect. One of the primary uses of an observational study is to help direct scientists to ask the right questions in subsequent research. Observational studies produce some of the weakest types of scientific data and are not intended to be used to inform clinical decisions, like what to eat, or not eat, to prevent cancer.
As is common in nutrition studies, researchers used food frequency questionnaires and diet recall as methods to find out what subjects ate.
Do you remember what you had for breakfast yesterday? How about how much and what you ate when you were a kid? Registered dietitian Abby Langer does a great job here of talking about the limitations of these tools that, honestly, no one in nutrition science loves – or even likes. But there really are not any great alternatives, so we still use them.
About this study, Ms. Langer noted:
“There were no fruit or vegetable intakes measured. Those who consumed more soy likely consumed more fruits and vegetables overall. That’s my guess, but unfortunately the study didn’t bother reporting that metric (if they measured it at all). Diet quality wasn’t measured, either.
The study did show that the women who consumed milk were also heavier, ate more processed red meat, and were less active.”
This leads right into another significant limitation of this study: body mass index. BMI was measured just once at the beginning of the study, so the researchers had no way of knowing if the women who were diagnosed with breast cancer also gained more weight during the study time frame. This is very significant because it is well-established that overweight and obesity are correlated with post-menopausal breast cancer.
On the plus side, this was a large and relatively long study, as it followed almost 53,000 women over nearly 8 years.
But no matter how big or how long, the study design simply cannot allow the researchers to conclude that drinking dairy milk causes cancer.
To come to this conclusion with any degree of certainty, much more research would need to be done and, in fact, much has been.
Researchers have been trying for decades to determine what, if any, link there might be between drinking milk and getting breast cancer. Yet, pooling data from more than two dozen studies that followed hundreds of thousands of women over many years has not provided a clear answer.
Some studies saw a possible increase in risk, some found no relationship at all, and others even suggested consuming moderate amounts of milk and dairy products might be protective against breast cancer. Given these weak relationships, if any risk for breast cancer from dairy exists, it is likely to be very small. We just don’t know, but it’s not for a lack of trying.
The American Institute for Cancer Research, a non-profit organization that funds cancer research and translates it into practical tools and information to help consumers prevent and survive cancer, publishes up-to-date summaries called Continuous Update Project (CUP) reports. In their CUP report for breast cancer, the key findings were:
- Adult weight gain and excess body fat increase risk for post-menopausal breast cancer.
- Alcoholic drinks increase the risk of post- and pre-menopausal breast cancers. Note: Alcohol is a class I carcinogen, meaning it is known to cause cancer.
- Regular vigorous physical activity reduces the risk of both post- and pre-menopausal breast cancers.
- Moderate physical activity reduces the risk of post-menopausal breast cancer.
- Breastfeeding reduces the risk of both post- and pre-menopausal breast cancers.
- For pre-menopausal breast cancers, body fatness was found to decrease risk.
If you’re wondering what you can do to reduce your risk for breast cancer or its recurrence, and are not already doing so, you can take action on these findings.
As for what to do about this milk and dairy thing, consider that low fat milk and dairy products can be excellent, low-calorie sources of several nutrients important for women’s bone, and overall, health. These include an easy to digest and absorb form of calcium, as well as vitamin D, several B vitamins, and protein.
It is quite possible to get these nutrients elsewhere from non-dairy foods in a well-balanced diet, but keep in mind that even calcium- and vitamin D-fortified plant-based milk alternatives are often lacking B vitamins and protein.
At the end of the day, even with this latest study, there just isn’t strong evidence that milk and dairy products are significant contributors to breast cancer risk or recurrence.
I will continue to counsel women to follow a well-balanced diet that includes plenty of fruits, vegetables, and whole grains, as well as a couple of servings of low fat dairy products. Additionally, I recommend limiting intake of calorie-dense, nutrient-poor foods and beverages, including alcohol, and staying as physically-active as possible.
Research consistently finds that women who do these things not only have lower rates of several types of cancer, including breast cancer, but these habits also reduce the risk for the number one killer of women – and men – cardiovascular disease (heart disease, high blood pressure, and stroke).
This is a win-win!
Angelea Bruce, RD, CSO, OPN-CG
Board Certified Specialist in Oncology Nutrition
Oncology Patient Navigator, Certified-Generalist
San Diego, CA