Ultra-Processed Foods May Increase the Risk of Breast Cancer
While considering this scenario, I recalled a recent case control study called the PRECAMA project,1 which involves teams of researchers from four countries: Chile, Colombia, Costa Rica, and Mexico. The study was coordinated by the International Agency for Research on Cancer. The study included 525 premenopausal women aged between 25 and 45 years. The women participating in the study had been diagnosed with breast cancer but had not yet begun treatment. Additionally, they had to have resided in the same district and been seen at the same health institution for the previous 3 years.
In a case control study, the researchers identify people without the condition or outcome of interest who are otherwise similar to those with the condition. In this study, the authors identified 525 women who also lived in the same district for the previous 3 years, attended the same health care institution, and were within at least 3 years of age of the matching participant.
All 1050 participants responded to questionnaires on general health and demographic information as well as specific variables such as the number of children they had and whether they breastfed those children, age at menarche, and smoking status. They also filled out a country-specific dietary questionnaire that asked the participant to estimate how often, over the previous year, they had consumed the specific food, with frequencies ranging from over six times per day to less than once a month/never.
The authors note that compared to those without breast cancer, a higher percentage of those women who had been diagnosed with breast cancer had no children or had their first child at an older age. They also breastfed for shorter periods and more often had a history of benign breast disease. They exercised less, were more highly educated, taller, and had a lower BMI.
What the authors were especially interested in for this article was the participants' consumption of processed foods. For the purposes of their analysis, the authors classified foods using a system developed in Brazil, with four levels:
- Unprocessed or minimally processed foods (fresh fruits and vegetables, unprocessed meat or fish)
- Processed culinary ingredients (olive oil, butter, sugar)
- Processed foods (canned fish, cheese, bread)
- Ultra-processed foods (processed meats, ready-to-eat/heat foods such as hot dogs or burgers, soft drinks, packaged sweets or snacks)
The authors grouped the participants' consumption of ultra-processed foods into three increasing levels of intake while also estimating the percentage of total calories those foods contributed to the participant's diet. In addition to the dietary questionnaire, for this article the authors also measured the levels of industrial trans-fatty acids present in the blood of a subset of participants, noting that those who reported consuming more ultra-processed foods had higher blood levels of harmful trans-fatty acids.
Compared to those who consumed the lowest amount of processed foods, the researchers found that "based on the proportion of calories intake from ultra-processed foods ... we calculated that an increase of 20% in calories from ultra-processed foods was related to a 46% increase in the risk of breast cancer."
For a woman consuming 1600 calories per day, 20% of those calories is just 320 calories. The authors noted that the greatest number of ultra-processed calories came from "industrial fruit juice beverages, industrial bread, breakfast cereals," snack foods, and margarine.
It's easy to consume 320 calories from ultra-processed foods: Fruit juice can contain about 90 calories per 8-ounce serving, some breakfast cereal can have about 140 calories per serving, and whole wheat bread can be 60 calories per slice (120 for a whole sandwich).
What’s The Take Home?
While case control studies offer weaker evidence than other types of studies, this should prompt you to look closely at just how much of your diet is ultra-processed foods. Beverages are an easy place to start, along with choosing the least processed breakfast cereals and healthier snacks such as fruits or vegetables rather than chips or cookies.
- Romieu I, Khandpur N, Katsikari A, et al. Consumption of industrial processed foods and risk of premenopausal breast cancer among Latin American women: the PRECAMA study. BMJ Nutr Prev Health. Published online January 4, 2022. doi:10.1136/bmjnph-2021-000335
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