Breast cancer prevention starts early
Jacob Schor ND, FABNO
March 5, 2016
In recent years a series of studies have been published that dietary habits during adolescent years play a major impact on breast cancer risk as an adult. While for most of our patients, this news is a bit late, it is nevertheless fascinating and certainly provides information of value to younger family members. We became intrigued with this focus of prevention initially by reading a paper by Maryam Farvid from the Chan School of Public Health at Harvard.
Farvid and her colleagues conducted a retrospective study that utilized data generated by the Nurses Health Study to determine multivariable-adjusted Cox proportional hazards modeling relative risks for breast cancer based on how much dietary fiber was consumed during adolescence. In simpler words, they dug up information on breast cancer patients and compared what these women ate decades ago to what women who didn’t get cancer ate.
This data came from the Nurses Health Study II (NHSII), an ongoing prospective cohort of 116,430 female registered nurses aged 25 to 42 when enrolled in 1991. Among the 90,534 premenopausal women who completed a dietary questionnaire in 1991, 2833 cases of invasive breast cancer were documented during 20 years of follow-up. In 1998, 44,263 of these women also completed a questionnaire about their diets during high school. Among this subgroup, 1,118 cases of breast cancer were documented.
There were statistically significant inverse associations between diet and cancer risk. Among all women, total dietary fiber intake during early adulthood was associated with significant 19% decrease in risk for breast cancer. Higher intakes of soluble fiber were associated with a 14% lower risk and insoluble fiber with a 20% decreased risk. Total dietary fiber during adolescence was also associated with 16% lower BC risk. Data on both adolescent and adult fiber intake were available for 41,092 women and when their average fiber intake was calculated for both periods, the RR comparing highest with lowest quintiles was 0.75, a 25% decrease in risk for cancer. 
In recent years it has become apparent that the progression to breast cancer starts early in life and that exposures during childhood and adolescence affect a woman’s long-term risk of breast cancer. We have seen a surge of studies that examine diet during pre-adolescence and adolescence that suggest that efforts at prevention may be more effective if begun in adolescence rather than in adulthood . 
Earlier studies suggested that caloric restriction, poor food quality, high total fat intake and high alcohol intake might increase risk but these studies were methodologically limited and the results inconsistent. The newer studies have hopefully overcome these weaknesses and provide useful guidance.
Breast cancer prevention must start earlier rather than later in life. “Breast tissue undergoes rapid cellular proliferation between menarche and first full-term pregnancy, and risk accumulates rapidly until the terminal differentiation that accompanies first pregnancy….. Breast cancer prevention efforts will have the greatest effect when initiated at an early age and continued over a lifetime.”
This paper just mentioned written by Maryam Farvid PhD and is the latest in a recent series on adolescent diet and adult breast cancer risk.
Liu et al reported in 2014 that dietary fiber, vegetable protein and nuts provide a protective benefit against breast cancer. A food frequency questionnaire was used in this Canadian cohort to compare diet followed between the age of 10 and 15 and the risk of diagnosis of breast cancer as an adult. Some 2,865 breast cancer cases were compared to 3,299 control cases and estimated odds ratios (OR) and 95% confidence intervals were determined through logistic regression. Inverse associations were found between intakes of dietary fiber, vegetable protein, vegetable fat, and nuts during adolescence with breast cancer risk, an association that persisted after controlling for adult intakes. In other words, eating dietary fiber, vegetable protein, vegetable fat, and nuts during adolescence was associated with reduced breast cancer risk. The ORs for the highest versus the lowest quintile of intake were 0.66 for fiber, 0.80 for vegetable protein, 0.74 for vegetable fat, and 0.76 (for ≥1 serving/day vs. <1 serving/month intake) for nuts. Again in simpler words, eating lots of fiber, vegetable protein, vegetable fat and nuts lowered risk of breast cancer by 34%, 20%, 26% and 24% respectively . 
The decreases in risk for breast cancer reported in this Liu paper are consistent with what Maryam Farvid reports in her paper.
A July 2015 study, also written by Farvid et al, failed to find a significant association between a high carbohydrate or high glycemic diet during adolescence with breast cancer risk. To their surprise they “… found that diets high in GI, GL, insulin index, and insulin load during adolescence or early adulthood were not associated with an increased risk of breast cancer in this cohort study…”  Carbohydrate consumption may be less of a problem than we might have thought.
These results are surprising because they seem to contradict a 2013 paper by Minicozzi et al that reported, “… high fasting blood glucose and obesity significantly and independently increase risk of breast cancer death in hormone receptor-positive disease” and that reported, “… in ER+PR+ patients, high blood glucose and high BMI are independently associated with increased risk of breast cancer death”. These results suggest that glycemic loads should play a role. 
The same team of researchers, Farvid et al., reported in April 2015, that meat consumption during adolescence “was significantly associated with higher premenopausal breast cancer risk”. When comparing the highest versus lowest quintile of consumption, high meat eaters had a 43% increase in relative risk (RR, 1.43; 95%CI, 1.05-1.94; Ptrend = 0.007). This association did not hold in postmenopausal breast cancer. Poultry was associated with lower risk of breast cancer overall (RR, 0.76; 95%CI, 0.60-0.97; for each serving/day). Replacement of one serving per day of red meat with one serving of combination of poultry, fish, beans or nuts was associated with a 15% lower risk of breast cancer overall (RR, 0.85; 95%CI, 0.74-0.96) and a 23% lower risk of premenopausal breast cancer (RR, 0.77; 95%CI, 0.64-0.92).
As a result of these recent studies we are accumulating knowledge that allows us to more accurately describe how a young woman should eat to lower breast cancer risk later in life. Their goal should be a diet that emphasizes dietary fiber, vegetable protein, vegetable fat, nuts and poultry and that decreases meat consumption by substituting fish, poultry or beans. Lowering glycemic load may or may not be useful.
1. Farvid MS, Eliassen AH, Cho E, Liao X, Chen WY, Willett WC. Dietary Fiber Intake in Young Adults and Breast Cancer Risk. Pediatrics. 2016 Mar;137(3):1-11.
2. Mahabir S. Association between diet during preadolescence and adolescence and risk for breast cancer during adulthood. J Adolesc Health. 2013 May;52(5 Suppl):S30-5.
3. Colditz GA, Bohlke K, Berkey CS. Breast cancer risk accumulation starts early: prevention must also. Breast Cancer Res Treat. 2014 Jun;145(3):567-79.
4. Liu Y1, Colditz GA, Cotterchio M, Boucher BA, Kreiger N. Adolescent dietary fiber, vegetable fat, vegetable protein, and nut intakes and breast cancer risk.
Breast Cancer Res Treat. 2014 Jun;145(2):461-70.
5. Farvid MS, Eliassen AH, Cho E, Chen WY, Willett WC. Adolescent and Early Adulthood Dietary Carbohydrate Quantity and Quality in Relation to Breast Cancer Risk. Cancer Epidemiol Biomarkers Prev. 2015 Jul;24(7):1111-20.
6. Minicozzi P, Berrino F, Sebastiani F, Falcini F, Vattiato R, Cioccoloni F, Calagreti G, et al. High fasting blood glucose and obesity significantly and independently increase risk of breast cancer death in hormone receptor-positive disease. Eur J Cancer. 2013 Dec;49(18):3881-8.
7. Farvid MS, Cho E, Chen WY, Eliassen AH, Willett WC. Adolescent meat intake and breast cancer risk. Int J Cancer. 2015 Apr 15;136(8):1909-20.