Women who eat a balanced low-fat diet
and daily portions of vegetables, fruit, and grains have a 21% lower risk of dying from breast cancer, according to research that will be presented at the 2019 American Society of Clinical Oncology (ASCO
Annual Meeting in Chicago.
The Women’s Health Initiative (WHI) Dietary Modification (DM) clinical trial set out to examine the impact of a low-fat diet on breast cancer incidence and mortality given the inconsistent findings of previous observational studies and the fact that countries with lower fat diets tend to see less instances of breast cancer.
In a press cast ahead of the meeting, lead author Dr. Rowan Chlebowski, of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, explained that this was the first large, randomized clinical trial to show that diet can reduce the risk of dying from breast cancer.
From 1993 to 1998, investigators enrolled 48,835 postmenopausal women ages 50 to 79, with no previous breast cancer history, from 40 clinical centers across the United States. These women also had diets where 32% or more of their calories came from fat.
Of the total, 29,294 (60%) women continued their usual diet
in the comparison group and were seen once a year by researchers, while 19,541 (40%) women were placed in a dietary intervention group, with the goal of reducing their daily fat intake to 20% of their calories and increasing their fruit, vegetable and grain intake. These women were seen at 18 visits over the course of a year, followed by quarterly follow-up visits.
The dietary intervention ended after 8.5 years (in 2005), and the trial has followed participants for a median of 19.6 years. Between 1993 and 2013, 3,374 cases of breast cancer were diagnosed in the entire trial population.
In the data to be presented at ASCO, researchers found that the women in the reduced-fat diet group saw more health benefits compared to those in the control group. Most notably, the risk of death from any cause after a breast cancer diagnosis was reduced by 15%, and the risk of death directly from breast cancer was reduced by 21%. Throughout the dietary intervention period of 8.5 years, investigators found 8% fewer breast cancer diagnoses overall.
As Chlebowski explained, this research shows that dietary changes can significantly influence a woman’s risk of dying from breast cancer. “The balanced diet we designed is one of moderation, and after nearly 20 years of follow-up, the health benefits are still accruing.”
Oncology dietitians Allie Spaay and Julie Balsamo, both from the John Theurer Cancer Center, also had positive things to say, but they cautioned that many factors are at play here.
“I think it is important to look at a few factors from this study that may have contributed to this impact,” said Spaay. “We cannot say for sure whether the low-fat component, the increased fruit, vegetable and whole grain component, or the probable calorie reduction was the primary influence of improved survival.”
“The women from the intervention group also lost weight and numerous studies show that obesity is associated with poorer prognosis and increased mortality from breast cancer,” she added.
Balsamo went on to offer tips for patients looking to tweak their own diets to lower their fat intake and increase their vegetable, fruit and grain intake.
“Fats play an important role within your body, but like all foods, they should be consumed in moderation,” she said. Some small changes that could have a big impact include choosing fat free or low-fat dairy products, limiting high fat cheeses such as brie and cheddar, and cooking at home with vegetable oils like olive and sunflower oils rather than butter or margarine.
Balsamo continued, “Protein-wise, aim for lean and plant-based proteins such as fish, poultry, legumes, nuts or seeds. And choose the right fats – not all fats are created equally.”
“While we want to stay away from saturated and trans-fats, healthy, mono-unsaturated and poly-unsaturated fats can help to fight inflammation and lower the risk for chronic disease. Opt for incorporating healthy fats such as salmon, mackerel, nuts, seeds and avocados into your diet.”
When it comes to incorporating more fruits, vegetables and grains into your daily diet, Balsamo suggests using whole grain varieties when cooking pasta or rice (such as quinoa or barley), doubling the amount of vegetables in any given recipe, and having pre-cut fruits and vegetables available to snack on when the urge strikes.
While the data cannot determine what factor was responsible for the benefits seen in this study, Spaay noted that the results are still encouraging. “This study helps us demonstrate it is important to focus on overall diet patterns and making sustainable changes to improve the diet as a whole,” she said.
“It is great that we have the opportunity to show women the evidence that the impact of diet can have on living a longer, healthier life.”