If you have any interest in health at all, you’ll be familiar with the concept of altering fat intake to reduce risk of disease and premature death. One central theme here is that certain types of fat (e.g. saturated fat) increases risk of ‘cardiovascular’ diseases such as heart disease and stroke, while others (e.g. polyunsaturated fats) have a protective effect. Either replacing saturated fat with polyunsaturated fat and/or reducing fat overall is supposed to be good for our health – but is it?
In recent years there have been quite a number of studies which have failed to find a link between saturated fat and cardiovascular disease. These studies cast considerable doubt on the wisdom of cutting back on saturated fat.
Yet, studies such as these that are ‘epidemiological’ in nature and only tell us of a lack of a relationship between saturated fat and cardiovascular disease. To really know whether cutting back on saturated fat and/or replacing it with supposedly healthier fats is beneficial to health we need to conduct studies that test just that, with what are known as ‘intervention’ studies.
Many studies of this type have been conducted over the last few decades. These were reviewed back in 2000 by a group of British researchers [1]. This review was actually a ‘meta-analysis’ (grouping together of similar studies) of 27 individual studies. The results revealed that modification of dietary fat did not lead to a significant reduction in either deaths due to cardiovascular disease or overall risk of death.
This meta-analysis was recently brought up-to-date by the same group of researchers [2]. Another decade’s worth of data was added in the form of another 21 studies. The studies in this review basically came in three forms:
1. studies where fat intake was reduced (usually by replacing fat with starchy foods) compared to usual or ‘control’ diet
2. studies where fat intake was modified (e.g. saturated fat replaced with polyunsaturated fat)
3. studies where fat intake was both reduced and modified
Let’s take a look at the results:
Reduction of dietary fat, modification of dietary fat, or both did not reduce the risk of death due to cardiovascular disease.
Reduction of dietary fat, modification or dietary fat, or both did not reduce overall risk of death.
The authors of this study report that there was evidence that reduction and/or modification of fat led to a significant reduction in risk of ‘cardiovascular events’ (basically a collection of fatal and non-fatal heart attacks and strokes). However, before cracking open the champagne, there’s a couple of things worth bearing in mind here.
First of all, dietary fat change did not lead to a significant reduction in risk of either heart attack or stroke when taken in isolation.
Also, some of the studies used in the analysis did not just employ changes in dietary fat, but other strategies too (for example, nutritional supplements were given to the treated group). This obviously makes it impossible to discern what elements of the treatment were effective.
Crucially, when such studies were removed from the analysis and studies that utilised fat modification were used, overall risk of cardiovascular events was not changed at all.
Here’s an interesting excerpt from the authors’ discussion:
“It is important that individuals and populations are receiving clear, evidence-based advice about the types of dietary fat changes which are most effective in reducing cardiovascular risk, as well as ways to achieve those changes. Further research comparing low fat and modified fat changes on cardiovascular disease risk factors would be feasible and helpful. This review suggests that modified fat intake, or modified and reduced fat intake combined (but not reduced fat intake alone) are protective against combined cardiovascular events. No clear effects of these interventions on total or cardiovascular mortality were seen.”
I’d agree regarding the importance of the public getting evidence-based advice. But why the need for further research? Are the results not clear? The pooled results of 48 studies show that low-fat eating or replacing saturated fat with polyunsaturated fats is an unmitigated failure. Why do we need more research? In the hope of keeping the fallacy alive?
What do the authors mean when they say “No clear effects of these interventions on total or cardiovascular mortality were seen.” Let me reword this line for the authors and call a spade a spade: “Conventional dietary advice regarding fat consumption has been proven to have no effect on risk of heart attack or stroke or cardiovascular mortality or total mortality – they don’t prevent disease nor save lives. We should abandon them.”
References:
1. Hooper L, et al. Dietary intake and prevention of cardiovascular disease: systematic review. BMJ 2001 322(7289):757-630
2. Hooper L, et al. Reduced or modified dietary fat for preventing cardiovascular disease.
Cochrane Database Syst Rev. 2011 Jul 6;7:CD002137.
