More Research Questions Link Between Saturated Fat & Mortality

“Saturated fats are not associated with all cause mortality, cardiovascular disease, coronary heart disease, ischemic stroke, or type 2 diabetes”¹. That’s the bold and somewhat startling concluding sentence from the latest major review study to evaluate the link between intake of saturated fat and the risk for leading causes of death. The study follows hot on the heels of two other high profile studies that involved reviews of randomised trials examine the role of saturated fat intake in risk of major disease^{2, 3}.

In science it’s easy to dismiss one study, even if it employs sound methodology. Before scientist start claiming that something is ‘scientific fact’, they ideally like to see initial findings verified by several other independent studies. But with the publication of three major separate independent studies in the space of 12 months^1-3, even the harshest sceptics will be forced to have a hard look at the new evidence and re-evaluate their stance/position on the issue.

Interestingly though, the other major finding to emerge from this latest study published on the 12^th August 2015 in the prestigious British Medical Journal, was that trans fatty acid intake was associated with all cause mortality, total cardiovascular disease, and coronary heart disease mortality.

‘Partially hydrogenated vegetable oils’ is a common ingredient known to contain trans fats, with elaidic acid being the major occurring one. Common sources of trans fat such as elaidic acid are margarine and fried foods, although many food companies and fast food chains (i.e. McDonald’s & KFC) now have trans fat-free version of french fries and fried chicken.

So avoiding trans fat intake is not as simple as avoiding fried foods. This is highlighted by findings of another study published in the British Medical Journal in which the relationship between consumption of fried foods and risk of coronary heart disease was examined in a Spanish cohort. Spaniards typically use olive and sunflower oils which are much less prone to trans fat formation when used for frying than say cheap vegetable oil. This was thought to largely explain the lack of association between intake and heart attack risk in this Mediterranean country⁴.

In contrast, a recent study looking at the impact of fried food consumption as part of a so-called ‘southern-style’ diet found  a significant positive link between risk of heart disease and consumption of fried foods⁵. But in contrast to the above study that involved a Spanish cohort, the ‘Southern’ subjects in this study were predominantly African-American and residents of southern states of America. In contrast with Spain, this region of the US is not known for their use of high quality vegetable oils such as olive and sunflower, but rather cheaper oils that are more prone to trans fat formation and content.

So while the traditional advice to consume minimal saturated fat to reduce one’s risk of major disease seems in desperate need of review, it’s important to highlight that consumption of fat in the form of trans  fats (from fried foods and the like) still represents a significant risk for heart and associated chronic disease. It’s likely that the type of oil, the degree of thermal degradation of the oil, and the type of food likely affect the production of trans fatty acids during the frying process and, as such not all fried foods have the same nutritional value.   

1. de Souza RJ, et al. Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ. 2015;351:h3978.
2. Chowdhury R, Warnakula S, Kunutsor S, et al. Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Ann Intern Med. 2014;160:398-406.
3. Harcombe Z, Baker JS, Cooper SM, et al. Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis. Open Heart. 2015;2:e000196.
4. Guallar-Castillón P, et al. Consumption of fried foods and risk of coronary heart disease: Spanish cohort of the European Prospective Investigation into Cancer and Nutrition study. BMJ 2012;344:e363
5. Shikany JM, et al. Southern Dietary Pattern is Associated with Hazard of Acute Coronary Heart Disease in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study. Circulation. Aug 10. [Epub ahead of print]