Is "Bad" Fat Now "Good"?
Len Kravitz, Ph.D.
Introduction
No doubt personal trainers were surprised and confused after reading or hearing about a recent study published in the Annals of Internal Medicine challenging the long-held association between saturated fat intake and heart disease. Some of the media reports pounced on the study results, giving green light messages to eat more red meats and butter. This is a controversial research topic due to various limitations of clinical studies, such as subject compliance to a long-lasting dietary regimen, that have investigated the relationship of fat intake and cardiovascular disease (Siri-Tarino et al., 2010). Yet, this recent study stirred up considerable attention. Further analysis of this health issue suggests caution is advised before exercise professionals give clients the go ahead to start indulging on saturated-fat containing foods.
The Study That Challenges The Association of Saturated Fat to Heart Disease
A team of researchers led by a Rajiv Chowdhury (2014), a medical doctor and researcher from the United Kingdom conducted a meta-analysis and systematic review of the combined data from 76 studies. A meta-analysis is a statistical method that combines results from different studies with the objective to provide a precise estimation of the effect of a treatment, risk factor for a disease, or possible other clinical outcomes (Haidich 2010). Haidich continues that this statistical measure also attempts to identify consistencies, interrelationships, or contrasts between the studies analyzed. However, meta-analysis study designs are often criticized for how researchers choose to include the studies that were selected and how the data are evaluated.
The Chowdhury investigation combined data from 27 randomized controlled trials of fatty acid supplementation, 17 observational studies of fatty acid biomarkers, and 32 observational studies of fatty acids from dietary intake. Chowdhury and colleagues' controversial finding from their study was that the evidence does not support current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats, for the reduction heart disease.
What's the Message from the American Heart Association and American College of Cardiology?
Interestingly, on November 13, 2013 the American Heart Association (AHA) and the American College of Cardiology (ACC) published a joint position stand on healthy living (Eckel et al. 2013). The scientific evidence supporting this position stand is from 133 studies published between 1990 and 2012. This joint organization statement recommends all adults to get physically active and eat a heart-healthy diet to prevent heart attacks, strokes and other cardiovascular diseases. For physical activity the AHA and ACC encourage all adults to average 40 minutes of moderate to vigorous-intensity aerobic exercise (such as brisk walking), three to four times a week. With diet, the joint statement encourages following a heart-healthy lifestyle by eating more fruits, vegetables, and whole grains, while including low-fat dairy products, poultry, fish and nuts,
In regards to LDL cholesterol or the “lousy” cholesterol that is elevated from saturated fat intake (See next section for more), the AHA and ACC statement states that 33% of adults have elevated levels of this harmful cholesterol. The researchers from this joint position paper highly encourage limiting trans fat and saturated fat because of the increased risk of heart disease (i.e., disputing the Chowdhury et al., 2014 findings). Trans fats can be found in many foods, particularly in commercially baked foods such as pastries, pie crusts, biscuits, pizza dough, cookies, crackers, and in fried foods (like French fries). Saturated fat can be found primarily in foods derived from animals, such as fatty cuts of meat and poultry with skin, full-fat dairy products, coconut and palm oil. A highly cited research study published in the American Journal of Clinical Nutrition (Jakobsen et al., 2009), which pooled data from 11 studies from Europe and America, supports the AHA and ACC recommendations. Jakobsen and colleagues conclude that replacing saturated fatty acids with polyunsaturated fatty acids, rather than monounsaturated fatty acids or carbohydrates, helps to prevent coronary heart disease.
How Does Saturated Fat Elevate LDL-Cholesterol?
Dietary intake of saturated fat intake has been shown to increase LDL cholesterol, and thus has been consistently associated with an increased risk of cardiovascular disease (Siri-Tarino et al., 2010). LDL cholesterol particles can be separated into two types that differ in size, density, chemical composition, metabolic behavior and atherogenic risk (Rizzo & Berneis, 2006). Rizzo and Berneis explain the types have been called 'pattern A' (larger, more buoyant LDL) and 'pattern B' (smaller, denser LDL). Smaller, denser LDL particles in particular have been shown to be highly associated with atherosclerotic plaque build-up and a predictor of cardiovascular disease (Siri-Tarino et al., 2010; Rizzo & Berneis, 2006). Rizzo and Berneis continue that LDL size is genetically influenced, with studies showing heritability ranging from 35-45%.
It should be noted that much of the basic science research on LDL atherosclerotic mechanisms explaining this association has been completed in animal studies. Siri-Tarino explain that the studies in animals have shown that saturated fats increase LDL cholesterol by inhibiting a special LDL receptor activity and enhancing production of apolipoprotein B-containing lipoprotein. This LDL cholesterol-raising effect of saturated fatty acids has been shown to be associated with high levels of dietary cholesterol consumption. When individuals or animals are fed (or eat) excessive calories and dietary cholesterol, specific saturated fatty acids can contribute to this decreased LDL receptor activity (Siri-Tarino et al).
Siri-Tarino et al. (2010) report the replacement of saturated fat with polyunsaturated fat has been shown to decrease total cholesterol and LDL cholesterol by lowering LDL cholesterol production rates and/or increasing LDL clearance rates from the blood. Lastly, the authors summarize these benefits are likely to be underestimated because polyunsaturated fats can have other benefits beyond cholesterol, including improving insulin sensitivity and reducing inflammation.
Where Do We Go From Here?
This saturated fat controversy is a meaningful moment of awareness for the fitness industry. Perhaps we need to re-focus and realize that although this issue is an important research concern to resolve, one overarching goal of what we do in our profession is to help reduce the risk of cardiovascular disease worldwide. This requires a concerted effort for each client to learn how to integrate optimum physical activity, exercise and dietary plans into a sustainable lifestyle. Realistically, it is not beneficial for a client to go on a reduced saturated fat dietary regime if she/he just replaces those fats with refined sugars. This is just replacing one risky foodstuff with another one. As personal trainers we can educate and guide our clients to make sensible and evidence-based lifestyle decisions that will improve their quality of life and protect against the cardiovascular disease.
References:
Chowdhury, R., Warnakula, S., Kunutsor, S., Crowe, F. et al. (2014). Association of dietary, circulating, and supplement fatty acids with coronary risk: A systematic review and meta-analysis, Annals of Internal Medicine, 160(6), 398-406.
Eckel, R.H., Jackic, J.M., Ard, J.D., Hubbard, V.S et al. (2013). 2013 AHA/ACC guidelines on lifestyle management to reduce cardiovascular risk: A report of the American College of Cardiology/American Heart Association task force on practice guidelines
http://circ.ahajournals.org/content/early/2013/11/11/01.cir.0000437740.48606.d1
Retrieved June 22, 2014
Haidich, A.B. (2010). Meta-analysis in medical research, Hippokratia 14(Suppl 1), 29-37.
Jakobsen, M.U., O'Reilly, E.J., Heitmann, B.L., Pereira, M.A. et al. (2009). Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. American Journal of Clinical Nutrition, 89:1425-32.
Rizzo, M., Berneis, K. (2006). Low-density lipoprotein size and cardiovascular risk assessment. Quarterly Journal of Medicine, 99, 1-14
Siri-Tarino, P.W., Sun, Q., Hu, F.B., & Krauss, R.M. (2010). Saturated fatty acids and risk of coronary heart disease: Modulation by replacement nutrients. Current Atherosclerosis Reports, 12, 384-390.
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