For decades, we’ve been told that cutting fat from our diets is the key to a healthy heart. But a study published in Open Heart (a cardiology journal) digs into a massive trial from the 1990s called the Women’s Health Initiative Randomized Controlled Dietary Modification Trial (WHIRCDMT) and raises some big questions about that advice. Here’s what it means for you, in plain English.
The WHIRCDMT was a huge experiment that started in 1993, testing whether the U.S. government’s 1977 Dietary Guidelines—pushing a low-fat, “heart-healthy” diet—actually worked to prevent heart disease and other health issues. It focused on postmenopausal women and compared those eating a low-fat diet to those sticking with their usual eating habits.
The surprising takeaway? For women who already had heart disease when the study began, the low-fat diet didn’t help—it actually made things worse. In 2006, the first results showed these women had a 26% higher chance of heart problems on the low-fat diet compared to the control group. By 2017, with more years of data, that risk jumped to 47-61%. Ouch.
So, why didn’t this set off alarm bells? The researchers at the time brushed it off with some explanations—like saying these women didn’t stick to the diet well enough or weren’t on cholesterol drugs as often. But the Open Heart study argues those excuses don’t hold up. Even with many women in both groups taking statins (over 40%), the low-fat group still fared worse. Plus, the diet didn’t do much for other goals either—it barely helped with weight loss (just 0.4 kg after 8 years) and didn’t lower risks for breast or colorectal cancer. For women with type 2 diabetes, blood sugar control even got worse in the first year.
Here’s the kicker: sticking strictly to the low-fat diet was linked to more weight gain, while a higher-fat, lower-carb approach seemed to keep weight off better. That’s the opposite of what we’ve been told for years.
What does this mean for you? Well, it’s not a green light to drown everything in butter, but it does suggest that the “low-fat is best” rule might not be as solid as we thought—especially if you’ve already got heart issues. The study’s authors are calling out the need to rethink those old guidelines, pointing out they were based on shaky evidence to begin with.
For the average American, this is a reminder: nutrition advice isn’t one-size-fits-all. If you’re worried about your heart, talk to your doctor about what’s right for you—don’t just assume cutting fat is the answer. And maybe don’t feel so guilty about that extra slice of avocado toast!