Study Questions The Role Fat And Cholesterol Play In Heart Disease

| November 8, 2013 | Comments (0)

The conventional view is that saturated fat is ‘artery clogging’ and polyunsaturated vegetable oils are ‘heart healthy’. One way this concept can be tested is to put people on diets that are low in saturated fat or replace it with supposedly healthier fats. When you put such studies together, the results show no reduced risk of heart disease, stroke or overall risk of death [1].

This evidence strongly challenges our preconceived notions about saturated and ‘polyunsaturated’ fat. Every so often, though, someone will offer up a study that appears to buck the trend. One such study is known as the ‘Los Angeles Veterans Administration Diet study [2]. I recently had an exchange with a dietician who used it as ‘evidence’ of my faulty thinking on fats (I maintain that there is no good evidence to incriminate saturated fat, and that vegetable oils have not been proven to be inherently ‘heart healthy’. So, what was this study about, and what did it show?

The LA veterans study involved more than 800 middle-aged and elderly men (54-88 years) living in an institution in the US. Each participant was allocated to eat one of two diets:

1. a diet low in animal fat and cholesterol but enriched with polyunsaturated vegetable oils (corn oil, safflower oil, soya bean oil, and cottonseed oil)

2. a normal diet

The food was supplied in the centre’s canteen under-double blind conditions (neither the men nor the researchers knew which diet each participant was eating). Once assigned to the diet, men were considered as part of the study however long they lived at the centre subsequently. What this means is that it was possible for men who only ate the prescribed diet for a relatively short period of time (even a few days or weeks) to be included in the data analysis.

Another major failing of the study was that the diets of the men were not very controlled: dining room records reveal that, overall, only about half the meals the men ate were at the centre and therefore controlled. We really have no idea what they ate the rest of the time (good, bad or indifferent).

Each participant was allotted his diet on a random basis. This is done to ensure that the two groups being compared are equivalent in terms of characteristics such as age and general health. However, one critical area that the men were not was cigarette smoking.

For example, 45 men in the ‘healthy diet’ group smoked more than a packet of cigarettes a day, compared to 70 in the control group. Also, there were 99 non-smokers in the ‘healthy diet’ group, but only 86 in the control. The generally higher levels of smoking in the intervention group would bias the results in favour of this group of course.

The ‘primary outcome’ (pre-determined main measured outcomes) for this study was the number of cases of ‘sudden death’ and heart attacks. The difference between the groups was not significant. In other words, the researchers failed to find any benefit in terms of the main outcome they measured.

The researchers performed other analyses, including adding up all the deaths due to ‘cardiovascular’ causes such as heart attack, stroke, amputation and rupture of the aorta (the main artery in the body).

Lumping all these things together did produce a statistically significant result. However, crucially, the study failed to find any reduction in overall risk of death.
The fact that cardiovascular deaths were reduced but overall risk of death was not points to the possibility of an increased risk of death from non-cardiovascular causes. In this study, the ‘healthy’ diet appeared to increase the risk of cancer.

One might ask what the point of reducing cardiovascular disease is if, at the same time, it increases risk of cancer. But also, when we take a broader look at the evidence, we see there are no overall health benefits from swapping polyunsaturated fats for saturated [1]. This evidence clearly asks questions about the conventional view on the role fat and cholesterol in heart disease.

Here’s to a healthy heart

Dr John Briffa
for The Cholesterol Truth

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1. Hooper L, et al. (2012) Reduced or modified dietary fat for preventing cardiovascular disease. The Cochrane Library.

2. Dayton S, et al. Controlled trial of a diet high in unsaturated fat for prevention of atherosclerotic complications. Lancet. 1968;2(7577):1060-2.

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