Wednesday, April 16, 2014

The Women's Health Initiative

Studies Associated with the Trial 

The evolution of the Women's Health Initiative: perspectives from the NIH (1995) [1] (no access)
Design of the Women's Health Initiative clinical trial and observational study (1998) [2]
Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial (2006) [3] (this post only used this study) 

Participants and Diets 

48835 post-menopausal women, between 50-79, of diverse backgrounds and ethnicities were randomised to either a low fat diet or a control group. 

The low fat diet was intended to reduce total fat intake to 20% of calories and increase intakes of vegetables/fruits to 5 servings/d and grains to at least 6 servings/d”.  The comparison group received diet-related education materials”.  The low fat diet wasn’t calorie restricted, didn’t set weight loss goals, and didn’t try to alter fat composition. 

The groups were very similar at baseline, which is what you would expect with that many participants.  There was a significant difference in aspirin use, but I don’t think 17.4 vs. 18.1 is very noteworthy, which goes to show how much easier it is to attain statistical significance with a larger sample.  This leads me to the next point 

Results 

There were a few statistically significant differences between the groups in how the CVD risk factors changed over the 3 years, all in favour of the low fat group.  Once again, most of them aren’t that noteworthy as you can see below.  There was no difference in SBP, trigs, markers of IR and fibrinogen* 

 
Baseline
3 Years
Low Fat
Control
Low Fat
Control
BMI
29.1
29.1
28.8
29.2
Physical Activity (METs/week)
10.0
10.1
11.6
11.3
Diastolic Blood Pressure
75.9
76.0
73.1
73.6
Total Cholesterol (mg/dl)#
224.0
224.2
214.1
216.6
LDL-C (mg/dl)#
133.3
134.2
123.2
127.0
Total Carotenoids (µg/mL)
0.7
0.7
0.7
0.6
Factor VIII* (%)
131.0
129.1
130.0
131.6
* Increases blood coagulation in response to injury
# P < 0.001 

Nutrient intake changed the way you would expect.  The low fat group increased protein, carbs, fibre, folate and servings of fruits and vegetables and grains; while decreasing total fat (and all types roughly in proportion), dietary cholesterol and nuts.  They achieved the target for fruit and vegetables and were close to the fat target after 1 year, but compliance got worse as the study went on and they actually consumed fewer grains at 6 years than at baseline.  The control group also made similar changes in the diet but to a much lesser extent** 

 
Baseline
1 Year
6 Years
Target
Total Fat (%)
(SFA)
37.8
(12.7)
24.3
(8.1)
28.8
(9.5)
20.0
(Expected: 7.0)
Serves of Fruit & Vegetables
3.6
5.1
4.9
5.0
Serves of Grains
(Whole)
4.7
(1.1)
5.1
(1.4)
4.2
(1.2)
6.0
(No Target)

The low fat group tended to have fewer CVD endpoints, but none of the differences were significant
 
 
After doing a subgroup analysis the researchers found that those with hypertension were more likely to benefit from the LF diet and those with a history of CVD (3.4% of the women) were more likely to have an CVD endpoint on the LF diet (HR=1.26, CI=1.03-1.54, P<0.006) (I’ve got no idea why that’s the case) 

In summary, a low fat diet with more fruits and vegetables had a minimal effect on CVD risk factors and didn’t significantly reduce CVD in post-menopausal women 

* The low fat group had a modest weight loss and improvement in blood lipids which is contrary to ideas that low fat is responsible for the obesity epidemic and ruins blood lipids (mainly triglycerides).  It depends on what the fat in replaced with, and in this case the fat seems to be replaced by fruits and vegetables at least to some extent 

** Since refined grains are nutrient poor and most of the grains eaten by these women were refined, it’s surprising that there was no specification for whole grains 

*** In the subgroup analysis they also found that those who consumed less SFA and TFA and/or more fruits and vegetables had lower LDL-C levels and rates of CHD.  As I usually say, associations of this kind are probably just markers of compliance

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