Sunday, December 29, 2013

The Saint Vincent's Hospital Study

Studies Associated with the Trial

Blood Cholesterol and Coronary Heart Disease (1963) (no access)
The Effects of Two Low Fat Dietary Patterns on the Blood Cholesterol Level of Young Male Coronary Patients (1963) [1]
Modified-fat dietary management of the young male with coronary disease. A five-year report (1967) [2]
The 5-Year Experience of Modified Fat Diets on Younger Men with Coronary Heart Disease (1970) [3]
Ten-year experience of modified-fat diets on younger men with coronary heart-disease (1973) [4]
 
The 'Pilot Study'
 
100 men, aged 20-50 with confirmed myocardial infarction, were randomised to one of two diet groups.  Both groups were placed on a diet where 28% of calories came from fat.  “The fat content was achieved by eliminating certain dairy products, rich desserts and pastries, certain fried foods, and fatty meats” [2]
 
“Diet 1 contained 1 oz of a 50% mixture of corn-safflower oil”
“Diet 2 contained 1 oz of a 50% mixture of coconut-peanut oil” 
 
There were a few other differences between the diets: Diet 1 was allowed 8 fish and seafood meals, whereas Diet 2 was only allowed 1; and Diet 1 had a special margarine that was higher in PUFA, whereas Diet 2 had a regular margarine (there may have been differences in TFA, but I can’t tell) [1]
 
All overweight participants (73) were placed on a standard 1,200 calorie weight loss diet.  After the desired weight was attained they were randomly placed on their assigned diet [2].
 
[2]
Diet 1
Corn and Safflower
Diet 2
Coconut and Peanut
Protein (%)
20.4
20.7
Fat (%)
SFA/MUFA/PUFA
P/S Ratio
27.8
5.5/9.3/14.1
3:1
28.2
9.6/13.2/3.3
1:3
Carbohydrates (%)
51.8
51.1
Cholesterol (mg)
260
395
 
After 12 months both groups had a minor decrease in cholesterol but the difference between the groups was not significant, which wasn’t consistent with metabolic ward studies.  Thinking that the issue may have been compliance, the researchers gave the men frozen meals.  After another 12 months (2 years) the pilot study ended due to a lack of difference in cholesterol levels between the groups [2]

A New Comparison
 
The researchers then merged the two diet groups and added a matched, non-dietary managed control group of 100 participants, with fairly similar risk factors, but the control group had more heavy drinkers, smokers and heavy smokers.  This made the remainder of the study non-randomised.  None of the overweight members of the control group were placed on the 1,200 calorie weight loss diet [2] [3]
 
After 5 years the study group had an average 10% (24 mg/dl) drop in total cholesterol, whereas the cholesterol level in the control group didn’t significantly change.  There was still no significant difference in cholesterol between the two diet groups despite good dietary adherence [2] [3]
 
Interestingly, while the average cholesterol level in the control group stayed pretty constant, the cholesterol levels in the participants who died in the control group actually slightly increased, whereas the cholesterol level in the participants who survived slightly decreased.  The differences weren’t significant [2]
 
 
The study group had slightly more myocardial infarctions and slightly fewer deaths, although since the years of experience in the study group was much greater than the control group, the incidence rates per years of experience was much lower in the study group (37.7% fewer myocardial infarctions and 57.1% fewer deaths [2] 

Of the 9 deaths in the study group, 5 came from the corn + safflower oil group and 4 came from the coconut + peanut oil group, but we don’t know what the causes of death were or the differences in myocardial infarctions between the diet groups [2] 

 
However, in addition to the weight loss in the study group, smoking was another confounding variable.  Smokers had approximately twice the incidence rate of non-smokers.  The control group already had more smokers at baseline and the difference became more pronounced at the end of the study.  After 5 years there was a decrease in smokers in the study group (from 37 to 29) and an increase in the control group (from 47 to 59) [3]
 
It’s a shame, what started as a fairly good (but probably underpowered from number and age) RCT testing the diet heart hypothesis ended up as a basic, multifactorial diet intervention study, where one can’t really tease apart the effects of smoking, weight loss and perhaps other dietary factors from dietary fat reduction.  But as for the diet heart hypothesis, the researchers found that “the degree of unsaturation of the diet did not appear to influence serum cholesterol value or mortality” [2]

None of the meta-analyses included this trial.  While it started off testing the diet heart hypothesis, it ended up non-randomised, testing a broad dietary intervention with weight loss, was underpowered to compare differences between the two diet groups (which were randomised) and didn't report the causes of death or incidence of myocardial infarction in the two diet groups.
 
* Peanut oil is “unexpectedly atherogenic” in animal models of atherosclerosis, which seems to be due to peanut lectin [5]
 
** After a 5 year follow up period (10 years total) there were still significant reductions in cholesterol in the study group compared to the control group and 42.9% fewer deaths in the study group (16% vs. 28%) [4]

No comments:

Post a Comment