Sunday, November 17, 2013

The Evidence Against Saturated Fat

The Heart Foundation’s Summary of Evidence 

Shortly after Catalyst aired the Heart Foundation responded to the program.  The response included links to a document called ‘Summary of evidence. Dietary fats and dietary cholesterol for cardiovascular health’ (2009). 

They discuss many things in this document and unfortunately their evidence often comes from studies where the endpoints are blood lipids rather than cardiovascular events, cardiovascular mortality or better still, total mortality.  I’m just going to keep it to SFA >> CVD and replacing SFA with PUFA for CVD. 

In a summary we get this: 

Level of evidence
Saturated FA (SFA)
·         SFA intake is associated with CHD5
·         Replacing SFA with cis-unsaturated FA has a greater positive influence on CHD risk than replacing SFA with carbohydrates (CHO)6,7
·         Replacing SFA with n-6 PUFA to achieve a ratio of PUFA to SFA of greater than one will reduce the risk of CHD (1999 evidence statement retained)2

The rest of the stuff in the table for SFA was about SFAs and LDL-C and a lack of evidence for associations between SFA with stroke and “the susceptibility to thrombosis and arrhythmia or blood pressure” 

Reference 5 is a review for FSANZ was only included observational studies looking at SFA and CVD and clinical trials looking at SFA and blood lipids.  No randomised controlled trials.  Also on their scale the level of evidence (III-2) is quite poor 

Reference 6 is a review by Mozzafarian.  The SFA section has some observational studies, some SFA >> LDL-C studies and a short section on clinical trials: 

“Results of randomized trials replacing saturated fat with polyunsaturated fat (including two trials that added a high proportion of alpha-linolenic acid, an omega-3 polyunsaturated fat) have been inconsistent; no significant effect was seen in four studies [40,41,43,44], CHD risk was reduced in one study [45,46], and total mortality was increased in another [42] (Table 1).” 

Reference 7 is a meta-analysis looking at how fatty acids and carbohydrates effect blood lipids.  Nothing on actual disease 

Reference 2 is to a previous evidence statement in 1999, which I can’t seem to find.  If it’s anything to go by, its referenced here as well: “The consumption of SFA and increased LDL-C levels are associated with an increase in CHD,2,24 although the strength of this association has recently been questioned.5.  Reference 24 is the Nutrient Reference Values (NRV) for Australia and New Zealand.  It has a small section on SFA and CVD, which only consists of the diet heart hypothesis: there is evidence that SFA increased LDL-C and evidence that LDL-C is associated with an increased risk of CVD.  Very appropriately they finish up with: “Whether dietary intervention would bring about equivalent lowering of CHD mortality is unknown.” 

On a somewhat related note, in the section ‘Limit intake of foods high in saturated fat’, the new Australian dietary guidelines just mention SFA >> LDL-C, but then there’s nothing about SFA >> CVD.  They then mention that omega 3s are therapeutic, which is not only irrelevant to the section but also irrelevant to the debate of whether to replace SFA with omega 6s 

So far, it’s just observational studies showing an association between SFA and CVD, studies that find SFA increases LDL-C and a short review of a few randomised trials with no significant effects and inconsistent results.  Not too persuasive. 

After 2009 

However, in the response to Catalyst the Heart Foundation mentioned that some further evidence in support of their position has been published since the 2009 Position Statement which includes: 

The Cochrane Database of Systematic Reviews (Hooper et al), 2011, Reduced or modified dietary fat for preventing cardiovascular disease.

Mozaffarian et al, 2010, Effects on Coronary Heart Disease of Increasing Polyunsaturated Fat in Place of Saturated Fat: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Jakobsen et al, 2009, Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies

But they didn’t reference the studies below, what a surprise 

Ramsden, et al., 2010. n-6 Fatty acid-specific and mixed polyunsaturate dietary interventions have different effects on CHD risk: a meta-analysis of randomised controlled trials

Siri-Tarino, et al., 2010. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease.

The Meta-Analyses of Clinical Trials 

But let’s ignore Jakobsen et al and Siri-Tarino, et al because both are observational 

The Cochrane review found reducing saturated fat by reducing and/or modifying dietary fat reduced the risk of cardiovascular events by 14%” but “There were no clear effects of dietary fat changes on total mortality or cardiovascular mortality” 

Similarly, Mozzafarian, et al. found Combining all trials, the pooled risk reduction for CHD events was 19%” but “In secondary analyses restricted to CHD mortality alone, the pooled RR was 0.80 (95% CI 0.65–0.98). Evaluating total mortality due to all causes (2,472 events), the pooled RR was 0.98 (95% CI 0.89–1.08).” 

Whereas Ramsden, et al. found For non-fatal myocardial infarction (MI)+CHD death, the pooled risk reduction for mixed n-3/n-6 PUFA diets was 22% compared to an increased risk of 13% for n-6 specific PUFA diets. Risk of non-fatal MI+CHD death was significantly higher in n-6 specific PUFA diets compared to mixed n-3/n-6 PUFA diets (P=0·02). RCT that substituted n-6 PUFA for TFA and SFA without simultaneously increasing n-3 PUFA produced an increase in risk of death that approached statistical significance (RR 1·16; 95 % CI 0·95, 1·42).” 

In other words neither study referenced by the Heart Foundation found that replacing SFA with PUFA lowered total mortality, whereas the findings of Ramsden, et al. suggest that replacing SFA with omega 6 is likely to increase total mortality (seeing as both SFA and TFA were replaced) 

Here are the trials (that replaced SFA with PUFA) the meta-analyses included.  I’m also aware of the Anti-Coronary Club and St. Vincent's Hospital Study, does anyone know of any others? 

Cochrane 2012
Mozzafarian 2010
Ramsden 2010
Rose Corn Oil 1965

Anti-Coronary Club 1966

Los Angeles Veterans 1968
Medical Research Council Trial 1968
Oslo Diet-Heart Study 1970
St. Vincent’s Hospital Study 1973

Sydney Diet Heart Study 1978

Finnish Mental Hospital 1983


Minnesota Coronary Survey 1989
Diet and Reinfarction Trial 1989

St. Thomas Atherosclerosis Regression Study 1992

I will discuss each of these trials in future blog posts

No comments:

Post a Comment