Be Wise about Fats: Lessons from the Women's Health Initiative Study
Women's Health Initiative (WHI) Findings
The mammoth WHI study involving nearly 49,000 postmenopausal women just weighed in on the health benefits of eating a low fat diet: two thumbs down. After 8 years, women assigned to a low-fat diet had just as much breast and colon cancer and just as much heart disease as those who followed their usual way of eating (1-3). But don't think that these results mean we can forget about broccoli or pile on the fries.
Some Limitations of the Study
The design of the study, which cost taxpayers $415 million, has met with some criticism. For starters, obesity greatly ups the risk for heart disease and breast cancer, and over 70% of the participants had a weight issue. Yet weight loss was not a target of the study and many believe it should have been.
In addition, the women didn't meet study goals for increasing fruit and vegetables or cutting fat. They were supposed to substitute fruits, veggies and whole grains in place of the extra fat. But fruit & veggie intake for example went up by only 1serving daily, falling short of the 5 a day goal.
Women in both groups started out getting 35-38% of their daily calories from fat. Initially, the low fat group was able to get their fat calories down to 24%. But the levels soon crept back up to 29% and never hit the study's goal of 20%. That led some low-fat diet proponents to question the study's outcome, saying that fat levels simply weren't low enough to show any health benefits, or that disease risks might have been reduced if the women had started eating the diet at an earlier age and stuck with it longer.
It's the 'Kind' of Fat That Matters Most
In reality, though, the failure to achieve that 20% goal underscores how hard it is eat a diet truly low in fat. It means no dressing on your salad, and bagels without cream cheese! And since the study began in '93, our knowledge about the health effects of balancing the type of fats we eat has expanded greatly. Though the WHI study confirms that reducing fat alone isn't enough to impact heart health, many cardiologists have already moved on from the notion of controlling total fat to the idea that people should be eating different kinds of fat. We now know that cutting back on saturated fats and trans fats - while getting more of our fat from fish, nuts and olive oil - can favorably affect heart health. In the WHI trial women weren't asked to eat more "good fats" or less of the "bad fats" like saturated and trans fats. Even so, a trend toward lower heart disease risk showed up in those who did manage to eat fewer of the "bad" fats and more produce and whole grains.
It's also worth noting that the kind of fat we eat may influence our odds of getting other age-related diseases not examined in the WHI study such as macular degeneration (AMD). In the AREDS trial for instance, people with the highest intake of the omega-3 fats EPA and DHA (the kind found in cold water fish) cut their risk of developing advanced AMD in half.
Questions about Fat and Cancer Remain
Women on the WHI low fat diet did have a 9% lower risk of breast cancer, though the difference between groups didn't reach statistical significance, meaning that the finding could have occurred just by chance. If the amount of fat in the diet really does have a small preventive effect, it could still show up with time. The WHI investigators will continue to follow women to see if the risk reduction becomes more pronounced. The diet didn't impact the rate of colon cancer either, though the researchers did see a reduction in polyps (a precursor to this type of cancer). They'll also be watching to see if a colon cancer benefit emerges over time.
Putting the WHI Results into Perspective
What the WHI study tells us is that a moderate reduction of total fat in postmenopausal women didn't do anything for heart disease, stroke, and possibly breast cancer. It also says that how much we eat counts just as much as what we eat. But it doesn't tell us that a produce rich diet with a better balance of fats isn't healthful. We can eat that way by following the Mediterranean diet [see September, 2005 issue]. It's not only healthy, but realistic and achievable.
- Howard BV et al. Low-fat dietary pattern and risk of cardio-vascular disease: the WHI. JAMA 295(6):655-66, 2006.
- Beresford SA et al. Low-fat dietary pattern and risk of colorectal cancer: the WHI. JAMA 295(6):643-54, 2006.
- Prentice RL et al. Low-fat dietary pattern and risk of invasive breast cancer: the WHI. JAMA 295(6):629-42, 2006.
- Chew EY. presented at ARVO, Bethesda, Maryland; May, 2005.