Dietary Fat & Coronary Heart Disease - Why We May Just Be Chasing the Wind

Stephan Guyenet recently did a write-up/critique of a rather interesting meta-analysis done by Chowdhury et al. The authors of this study gathered, somewhat indiscriminately, 32 observational studies of ingested fatty acids, 17 observational studies of fatty acid biomarkers, and 27 randomized controlled trials of fatty acid supplementation.

What did Chowdhury and his cohorts conclude?

They surmised that...

• In observational studies that measured diet, only trans fat was related to cardiovascular risk.  Saturated, monounsaturated, and polyunsaturated fats were unrelated to risk.
• In observational studies that measured circulating concentrations of fatty acids, long-chain polyunsaturated fatty acids (DHA, DPA, EPA, AA) were associated with lower risk.  The dairy-fat-derived margaric acid (17:0) was also associated with lower risk.  No other fatty acids were related to risk, including trans fatty acids.
• In controlled trials, supplementation with omega-3 or omega-6 fatty acids did not alter risk.

What a mess of conclusions!  Some of the data collected by the authors suggests that only trans fat presents a problem in terms of cardiovascular risk.  Still yet, other data seems to indicate that polyunsaturated fatty acids and margaric acid lower your risk of cardiovascular disease, meanwhile, all other sources of dietary fat (including trans fats) yield neutral results.  Moreover, the highly beloved anti-inflammatory omega-3 polyunsaturated fatty acid (in addition to its infamous, inflammatory cousin omega-6) had no effect on cardiovascular risk (at least when supplemented)!

For the most part, I'll have to piggyback on Guyenet's critique, given that Chowdhury et jerks want me to pay to see anything more than a quaint, but rather not-so-transparent summary of their work.

Important Limitations

As Guyenet rightly points out in his critique, meta-analytical studies have some pertinent limitations -- i.e. the meta-analysis is comprised of studies with varying degrees of quality and design, and the meta-analysis can only be as good as the quality of sources it uses.  Since I can't access the study itself, I'm relying on Guyenet's assessment.  According to him, "inclusion criteria were very lax."

Important Conclusions

Of course, the authors' verdict on trans fat (at least in relation to the observational studies that measured dietary fat) doesn't surprise me at all.  I've seen ample evidence to suggest that trans fat, which is primarily a product of hydrogenated polyunsaturated oils, can cause problems.  Nevertheless, not all of the evidence the authors of this study looked at confirm the deleterious effects of trans fat.

Some interesting bio-chemistry of how you body processes dietary fats.

I was actually rather shocked that little to no benefit was found for supplementing with omega-3 polyunsaturated oil.  However, omega-3 can come from a variety of sources, and the source can effect its bio-availability.  Animal based sources (EPA & DHA) are much more efficiently utilized by the body than plant based sources (ALA) [Read this article by Chris Kresser to learn more].  Unfortunately for us, the authors of this study looked at animal based sources of omega-3; thus, things look rather bleak for omega-3 supplementation.  While I still hold to the position that we ought to try as best we can to maintain a proper balance between omega-6 and omega-3 in our diet, the conclusions gleaned via this meta-analysis suggest that this balance may not be as important as other health risk factors.  Even Guyenet seems somewhat bummed out by the poor showing omega-3 supplementation has demonstrated in recent research --

After considering new evidence and reviewing old evidence, I've gradually drifted away from the view that omega-6 polyunsaturated fat contributes to cardiovascular disease.  I still think it's probably a bad idea to eat a lot of refined seed oils-- the lipid equivalent of white sugar-- but I don't see much of an argument for avoiding whole nuts and avocados.  Recent controlled trials and meta-analyses have also dampened my enthusiasm for the idea that omega-3 fatty acids have a major impact on cardiovascular disease risk.  Either the trials weren't long enough to see protection, or omega-3 isn't as powerful as we had hoped.

Herein lies el problemo.

In regards to what the authors concluded about saturated fat, I'm not at all surprised.  Little evidence exists to suggest that saturated fat is a boogeyman.  As a matter of fact, there's very little evidence to indict or defend saturated fat.  Though Guyenet maintains caution in regards to a diet high in saturated fat, I'm inclined to think that it isn't an issue.  The only circumstance under which I would say you should cut back on your saturated fat consumption would be if you were consuming it to the detriment of essential fatty acids such as omega-3 and omega-6, and/or if you were consuming more calories than you ought to be eating, and this excess was coming from saturated fat.

While the more specific conclusions of the authors present "something to upset just about everyone," the overall inconclusiveness of their study suggest that we may be, more or less, chasing the wind whenever we set out to isolate one type of fat (or any other nutrient) as the chief cause of disease in Western society.  I don't think it's anything controversial to suggest that, if you're looking to reduce your risk of cardiovascular disease, first see if you can eliminate such things as smoking, high consumption of alcohol, processed hyper rewarding foods, excess stress, and chronic sleep deprivation before you start assessing whether omega-3 supplementation might improve your heart health.  Lifestyle is by far a better predictor of health risk than any one dietary factor alone (unless of course you have a penchant for eating arsenic.  Then we know exactly what killed you!).