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

Sunday, April 6, 2014

Low-Fat Diet in Myocardial Infarction (Ball, et al)

Low-fat diet in myocardial infarction (1965) 

Participants and Diets 

264 men, under 65, who had recently had their first heart attack, were randomised to one of two diet groups: a low fat diet or the control diet.  The low fat diet group were advised to eat only 40g of fat per day.  “The daily allowance included 14 g. (1/2 oz.) butter, 84 g. (3 oz.) of meat, 1 egg, 56 g. (2 oz.) cottage cheese, and skimmed milk. The nature of the fat consumed was not altered, nor were any additional unsaturated fats given”
 
We have a limited amount of data on what they actually ate, but we’re told the low fat group had a large reduction in fat (~ 45g vs. 110-130g*) and ate fewer calories (~ 1900-2000 vs. 2300-2600) compared to the control group
 
 

Those who were overweight (21% of controls and 15% of LF group) were put on calorie restricted diets.  In the control group the calories that were restricted mostly came from carbohydrate instead
 
* Even though they didn’t meet the target of 40g, it’s a good effort considering “the diet was often unpleasant” and there was a large difference between the groups
 
Results
 
Both groups, particularly the low fat group, lost weight and lowered their cholesterol.  (The reduction of cholesterol in the control group may have been due to weight loss) 

 
 
Low Fat Diet
Control Diet
Total Cholesterol
(mg/dl)
Baseline
260
266
6 Months
223
251
4 years
216
241
Weight
(lb)
Baseline*
161
166
6 Months
148
159
4 years
151
158
* This difference was almost significant (01 > p > 005)
** Unfortunately we aren’t told whether the differences were significant, but they probably were
 
Ultimately though, despite the large difference in fat consumption and the reduction in cholesterol levels, there was no difference in either relapses or death, both in the general study population (table VII), and among those with severe CHD (table VIII).  (Fortunately the people who assessed the CHD events in this trial were blinded)
 

Also, “the mean follow-up time to first relapse or end of trial was 3-04 years for the low-fat group, and 3-05 years for the control group”.
 

One might argue that the lack of difference was because the low fat group almost doubled their intake of added sugar, but the researchers found that carbohydrate and added sugar consumption wasn’t associated with relapses.  Although if you ignore the 0-5 g/day group in table VI (which I find difficult to believe) there’s a trend, but it’s not that exciting
 

Sunday, March 30, 2014

Low Fat and CHD

I originally didn’t think about writing on low fat and CHD because I didn’t see the point.  After all, throughout the literature and the dietary guidelines there was no suggestion that low fat diets would reduce the risk of CHD.  But then I don’t subscribe to pop science, where calories make you fat, protein damages your kidneys, fat clogs your arteries, carbs give you diabetes and everything causes cancer.  For most people fat (of any kind) still remains the villain in CHD. 

Remember that the three main lines of evidence against saturated fat were: 

1.      Observational studies
2.      Clinical trials measuring blood lipids
3.      Clinical trials measuring end-points (events and mortality) 

I’m going to briefly go through each of these as they relate to low fat and CHD 

Observational Studies 

The Australian National Heart Foundation’s ‘Summary of evidence. Dietary fats and dietary cholesterol for cardiovascular health’ (2009) cites a review by Mozaffarian as evidence for “there is no direct relationship between total fat intake and the incidence of CHD”. 

The Australian Heart Foundation later use a meta-analysis of cohort studies by Jakobson, et al as evidence against saturated fat.  The Jakobson, et al meta-analysis found that replacing SFA with PUFA was associated with less CHD events and death, but replacing SFA with MUFA or carbohydrate had no effect* [1]. 

Another meta-analysis of cohort studies by Skeaff & Miller found that intake of total fat wasn’t significantly associated with CHD events or CHD mortality [2]. 

And finally, there’s also the well-known meta-analysis of cohort studies by Siri-Tarino, et al, which found “no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD” [3] 

* So if you’re going to debate the National Heart Foundation I don’t think you should spend much time arguing against low fat diets, because they will simply say that they don’t recommend a low fat diet, which is exactly what they did on Catalyst.  I would rather argue that (1) it’s unwise to make recommendations from observational studies and clinical trials measuring blood lipids; and (2) the better controlled fat modification trials don’t support the DHH and suggest some harm.  If you want to argue that they are recommending a low fat diet (because it seems most people challenging mainstream advice are pro-low carb), please define what ‘low fat’ means (I’ll be providing my take in a future post), otherwise it’s going to be one of those pointless ‘yes you are, no I’m not’ type of debate 

Clinical Trials Measuring Blood Lipids 

Two meta-analyses of clinical trials found that replacing fat with carbohydrate increases the total cholesterol to HDL-C ratio* [4] [5], which is perhaps the best CHD risk factor based on blood lipids [6]
 
 
* Only palmitic acid and artificial TFA increased the ratio, but the fats in food are comprised of many different fatty acids so even fat sources high in palmitic acid and/or artificial TFA like butter, shortening and palm oil reduce the total cholesterol to HDL-C ratio relative to carbohydrate 

** They also found replacing fat with carbohydrate increased triglycerides [4] [5] 

Clinical Trials Measuring End-Points (Events and Mortality) 

But we shouldn’t dismiss low fat diets based on findings of observational studies and their effect on blood lipids.  Just as it’s wrong to use observational studies to ‘prove’ there is an effect, it’s also wrong to use them to ‘prove’ there isn’t one either 

To my knowledge, there are two main meta-analyses looking at low fat (fat reduction) and CHD: the same Hooper, et al meta-analysis and the meta-analysis by Skeaff & Miller (who also did one for the fat modification trials*).  The results of the meta-analyses are in the table below: 

 
CHD Events
CHD Mortality
Total Mortality
Hooper, et al
0.97 (0.87, 1.08)
0.96 (0.82, 1.13)
0.97 (0.90, 1.04)
Skeaff & Miller
0.93 (0.84, 1.04)
1.00 (0.80, 1.24)
0.98 (0.90, 1.06)

Skeaff & Miller only included a trial by Ball, et al and the Women’s Health Initiative (WHI), while Hooper, et al included several others that were either very small (only a few events or deaths in each group), for cancer (mostly breast cancer and one bowel cancer) and one (the DO IT trial) that looks more like a fish oil trial.  So I’m only going to do Ball, et al and the WHI. 

This won’t limit me (or Skeaff & Miller) that much.  The WHI was a huge trial, lasting 8.1 years with 46,558 participants.  Consequently the WHI has well over 50% of the weighting in statistical analyses, which is probably a main reason why the results of the two meta-analyses are so similar, even though Hooper, et al included several other trials 

* They included Rose (but only compared olive oil to corn oil), LA Vets, MRC, Oslo, Finnish, DART and STARS and found for: CHD events RR = 0.83 (0.69, 1.00), p = 0.073; CHD mortality RR = 0.84 (0.62, 1.12), p = 0.335; and total mortality RR = 0.88 (0.76, 1.02), p = 0.005.  The somewhat positive result isn’t surprising considering their poor trial selection (pretty much as bad as Mozaffarian, et al) 

** My main objection to the fat modification trials was that the trials changed a lot more than SFA and PUFA intakes.  Some accidental changes would be expected when you make a dietary change.  For example: you would expect the control group (higher SFA) to have a higher vitamin A and cholesterol intake and the experimental group (higher PUFA) to have a higher vitamin E intake.  Other changes, like the amount of hydrogenated oil and junk food, is not expected and makes for a poorly controlled trial.  In the fat reduction trials you would expect the low fat diet would have more accidental changes, like increasing intake of vegetables, fruit and grains, as a function of increasing carbohydrate intake 

Summary 

Despite the dogma that ‘fat will clog your arteries’, low fat diets wouldn’t be expected to reduce CHD based on both observational studies and their effect on blood lipids.  Also, low fat diets haven’t been found to reduce CHD events, CHD mortality or total mortality in clinical trials.

Tuesday, March 25, 2014

Some Criticisms of the Paleolithic Diet Trials

There are a number of potential criticisms of the Paleo diet trials that I want to address 

Define Paleo 

Paleo is poorly defined 

Paleo critics are quite hypocritical on this point.  On the one hand they want a unified definition, but criticise it for being inflexible and say stuff like: ‘you can’t promote The Paleo diet because the diets of hunter-gatherers varied by geography and season and sometimes by a great deal’ and “chucking the many different hunter–gather diets into a blender to come up with some kind of quintessential smoothie is a little ridiculous”. 

Never mind that the Paleo community acknowledges the diversity of hunter-gatherer diets.  I also don’t understand the last objection.  If we draw a made up Venn diagram (below) to symbolise the differences between HG diets, then there are going to be many areas of common ground.  What’s so bad about finding value in the common ground?
 

What Paleo Diet? 

The Paleo diet used in the trials is very different to the Paleo diet that is being promoted 

I agree, but I don’t think it’s so black or white.  If people could only promote the exact diet people adhered to in clinical trials we would have a lot of half-assed diets and a lot of recommendations that lack evidence to support them, such as SFA and salt restriction in the Paleo trials. 

There are some people who describe the Paleo diets in the trials as something they’re not, and then use them as evidence to support their position.  That’s clearly dishonest and wrong.  But I can’t see the harm in using these studies to say: 

‘The Paleo diet (which contained A, but not/restricted/reduced B, with emphasis on C) used in these trials was more successful at doing X than the Mediterranean/Diabetes (whatever) diet (which contained D, but not/restricted/reduced E, with emphasis on F).  Since there were many differences between the two diets, it’s very difficult to know for sure which particular difference(s) was/were responsible for the difference(s) between the groups.  The Paleo diet used in the trials is similar to, but also different from the diet that I recommend.  Here are my reasons for how the diet I recommend differs from the Paleo diet in the trials… 

Obviously that won’t fit in a tweet 

For example: one of the main points of this objection is that the Paleo diet in the trials is low in SFA, but as it’s more commonly promoted, the Paleo diet doesn’t have restrictions on SFA.  So it would be dishonest and wrong to use these trials as evidence that SFA is ok (obviously), but there shouldn’t be a problem with using other sources of evidence (the fat modification trials) as support for SFA being ok.  As long as they acknowledge that cholesterol levels in the Paleo group would have been slightly higher if the SFA content was higher 

* Just in case you’re not aware here are some of the differences.  The Paleo diet used in the trials is a lot more consistent than the various incarnations of Paleo as it’s more commonly promoted, so the last column depends a lot on who you’re talking to (especially regarding macronutrients, dairy, fruit and starch).  Many popular versions of Paleo also include some variation of things like cured meats, fermented foods, some dark chocolate, other parts of the animal and ‘Paleo’ junk food (which should be an oxymoron) 

 
The Paleo Diet in the Trials
The Paleo Diet as it’s more Commonly Promoted
Macronutrients
High protein, moderate fat, moderate carb.  Low SFA, high MUFA and PUFA
Moderate-high protein, high fat, low carb.  High SFA and MUFA, low PUFA
Ad Libitum Foods
Lean meats, fruit, vegetables
Fatty meat, non-starchy vegetables, eggs, fats (mostly animal fats, olive oil and coconut oil)
Moderate Amounts Of
Eggs, potatoes, nuts, olive/canola oil
Dairy, fruit, starchy vegetables, salt
Restrict
Grains, legumes, dairy, refined sugar, salt
Grains (except white rice), legumes, refined sugar

The Trials Aren’t Well Controlled 

There are many differences between the two diets in the Paleo diet trials, so we don’t know what effect each variable has 

I completely agree.  My main complaint against the fat modification trials was that the experimental groups did more than just replace SFA with PUFA.  They were all advised to restrict TFA, many of them were advised to eat less junk food (baked goods, ice cream) and some were also advised to eat more whole foods (fruits, vegetables, etc).  So how could you say the differences in outcomes were due to fat modification rather than something else that was altered? 

Same thing is true in the Paleo trials where the Paleo diet tends to be: 

·         Higher in fruit, vegetables and meat, but lower in grains and dairy
·         Higher in protein, but lower in calories, carbohydrate and saturated fat 

If there’s a difference in outcomes between the groups we don’t know which of these factors was responsible.  Sometimes studies try to answer this by doing correlations, but I don’t think they are that useful.  Often they will really just be a marker of compliance, not only to grains/dairy/etc, but also to things like junk food and perhaps even exercise and other lifestyle factors. 

The bottom line is that the trials aren’t designed to say whether grains are bad.  Hopefully there will be a trial with a similar design to DART (multiple groups, each with a different combination of diet advice) to better test individual components and perhaps even examine whether there are any interactions 

Compliance 

Compliance was poor in the most recent trial, so you can’t really compare the diets 

I agree to some extent.  Metabolic wards and the more community based trials have their advantages and disadvantages.  Metabolic wards are better for measuring the actual diet (construct validity), while free living trials are better at measuring what will happen in real life (external validity).  You may have come up with the best diet, but in practice will people stick to it*?  If people find it too difficult to stick to the diet, then chances are that’s a problem of the diet. 

The recent Paleo trial had poor compliance in both groups.  I’m not sure if the level of compliance was better/worse than in other trials, but it was pretty bad and would have affected the results quite a bit.  Just to focus on the Paleo diet, the diet used is fairly difficult to adhere to (no grains and dairy is the main thing, but also lean meats and restricting salt**).  Perhaps the adherence, and then consequently the result would have been more favourable if some of the restrictions (like lean meats, low salt, low SFA and no cream and butter) were lifted.  Particularly those without much evidence to support them like low salt and low SFA (so lean meats). 

I imagine one of the main difficulties for dieticians is giving sufficient unpalatable advice to be effective, but not too much to be sustainable, and all of which depends on the person and their needs. 

* This is the issue with calorie restriction for weight loss.  Of course it works, but it’s very difficult to stick to long term. 

** I’m not counting legumes because people don’t eat much of them and don’t have the same desire for them as bread, pasta, baked goods, milk, cheese, butter, ice cream, etc. 

*** This isn’t only an issue for Paleo, but rather an issue for all dietary advice, whether it’s a particular diet, national dietary guidelines, etc.
 
Finally, there's also the issue of the trials only measuring stuff like weight and biomarkers, but not disease endpoints, which is a function of them being small and short