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There are two new diet studies out this week, and they add more evidence that when it comes to staying healthy, it may not be enough to just count those calories. What you choose to eat really does matter. NPR's Allison Aubrey reports on what researchers learned when they tracked the diets and health of thousands of women over two decades.
ALLISON AUBREY, BYLINE: When the Women's Health Initiative study began back in the 1990s, about 20,000 women were put on a diet. They were told to cut back on fatty foods such as red meat and full-fat dairy. And they were told to add in more plant-based foods. Here's study author Rowan Chlebowski of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center.
ROWAN CHLEBOWSKI: So we asked the women to eat more fruits, vegetables and grains but also to reduce their total fat intake.
AUBREY: Two decades later, what he and his colleagues have found is that women who were put on this diet had a 21% lower risk of death from breast cancer compared to women who didn't change their diets.
CHLEBOWSKI: This is significant because this is the first intervention study of any kind targeting breast cancer where a reduction in deaths from breast cancer has been seen.
AUBREY: The study adds to the evidence that what you eat can be an important driver of health. But it also raises new questions about exactly which changes the women in the study made that may have been most beneficial. Here's Jennifer Ligibel, a medical oncologist at the Dana Farber Cancer Institute.
JENNIFER LIGIBEL: There's been a lot that we've learned in the time since the study started about healthy fats and unhealthy fats.
AUBREY: At a time when we're told to eat plenty of healthy fats from sources such as avocados and olive oil, was it really an overall reduction in fat during the study that worked in the women's favor? Or was it due to other factors, such as all of the good nutrients and fiber that come from eating more fruits, vegetables and whole grains? Chlebowski says it's just not clear.
CHLEBOWSKI: We can't really separate out at the present time which component was important. But we have bloods on all 48,000 women, and now we will be examining a number of analyses to see if we can dissect out which were the important components.
AUBREY: So there's much more to learn. Now, one interesting point - the women in the study were not told to count calories or reduce calories. But overall, they did lose weight.
CHLEBOWSKI: We didn't target caloric intake reduction, but the women did reduce their weight by about 3%. So I think it's a message of dietary moderation.
AUBREY: The findings fit with another new study out this week that evaluated the effects of an ultra-processed diet compared to a minimally processed diet. It too finds that an overall healthy diet containing plenty of fruits, vegetables and whole grains can help prevent weight gain. Dariush Mozaffarian is dean of the Friedman School of Nutrition at Tufts University.
DARIUSH MOZAFFARIAN: The effects are really consistent with a lot of research coming out over the last decade that you can't judge a food by its calorie count.
AUBREY: And when it comes to eating healthy, the quality and range of foods you choose matter too. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.