No doubt personal trainers were surprised and confused after learning about a recent Annals of Internal Medicine study challenging the long-held association between saturated-fat intake and heart disease. Some media reports pounced on the study results, essentially giving green-light messages to eat more red meats and butter.
This is a controversial research topic because clinical studies that investigate the relationship between fat intake and cardiovascular disease always have limitations—such as how well study participants stick with a long-lasting dietary regimen (Siri-Tarino et al. 2010). Still, the recent Annals study stirred up considerable attention, so personal training clients may be talking about it. Further analysis of this health issue suggests exercise professionals should be cautious about giving clients the go-ahead to indulge in foods that contain saturated fats.
The Study That Challenges the Association of Saturated Fat With Heart Disease
A team of researchers led by Rajiv Chowdhury (2014), a medical doctor and researcher in the United Kingdom, conducted a meta-analysis and systematic review of data from 76 studies. A meta-analysis combines results from multiple studies to estimate as precisely as possible the effects of a treatment, disease risk factor or other clinical outcome, and it attempts to identify consistencies, interrelationships or contrasts between the studies analyzed (Haidich 2010). However, critics of meta-analysis study designs often question the specific choice of studies and the methods used to evaluate the data.
The Chowdhury investigation combined data from
- 27 randomized, controlled trials of fatty-acid supplementation,
- 17 observational studies of fatty-acid
- 32 observational studies of fatty acids from dietary intake.
Controversy erupted when Chowdhury and colleagues concluded that the evidence they analyzed did not support current cardiovascular guidelines that indicate “favorable effects on lipid profiles are greater when saturated fat is replaced by polyunsaturated fatty acids” (Eckel et al. 2013) for cardiovascular health.
What’s the Prevailing Position Stand From the American Heart Association and the American College of Cardiology?
Six months before the Chowdhury paper caused a stir, the American Heart Association and the American College of Cardiology published a joint position stand on healthy living (Eckel et al. 2013), backed by evidence from 133 studies published between 1990 and 2012. In their statement, the AHA and ACC encourage adults to get an average of 40 minutes of moderate to vigorous-intensity aerobic exercise (such as brisk walking) three to four times a week, and to eat more fruits, vegetables and whole grains, while including low-fat dairy products, poultry, fish and nuts.
In regard to LDL cholesterol, or the “lousy” cholesterol that rises in response to saturated-fat intake (see next section for more), the AHA and ACC say that 33% of adults have elevated levels of this harmful cholesterol. Authors of the joint paper highly encourage limiting trans fat and saturated fat because of their association with increased risk of heart disease. This is the conclusion Chowdhury et al. 2014 call into question.
Trans fats are common in commercially baked goods such as pastries, pie crusts, biscuits, pizza dough, cookies and crackers; and in fried foods like french fries. Saturated fats are most common in foods from animals—such as fatty cuts of meat, poultry with skin and full-fat dairy products—and in coconut and palm oils. An often-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, concluded 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?
Consuming saturated fat has been shown to increase LDL cholesterol, and thus has been consistently associated with a higher 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 that the types have been called “pattern A” (larger, more buoyant LDL) and “pattern B” (smaller, denser LDL) (see Figure 1). Smaller, denser LDL particles in particular have been highly associated with atherosclerotic plaque buildup and shown to be a predictor of cardiovascular disease (Siri-Tarino et al. 2010; Rizzo & Berneis 2006). Rizzo and Berneis say LDL size is genetically influenced, with studies showing heritability ranging from 35% to 45%.
It should be noted that much of the basic research on LDL atherosclerotic mechanisms explaining this association has been done on animals. According to Siri-Tarino and colleagues (2010), animal studies have found that saturated fat increases 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 people or animals take in excessive calories and dietary cholesterol, specific saturated fatty acids can contribute to the decrease in LDL receptor activity (Siri-Tarino et al.).
Siri-Tarino et al. report that replacing saturated fat with polyunsaturated fat has been shown to reduce total cholesterol and LDL cholesterol by lowering LDL cholesterol production rates and/or increasing LDL clearance rates from the blood. Last, the authors summarize that 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 presents a meaningful moment of awareness for the fitness industry. Perhaps we need to refocus and realize that although this issue is an important research concern to resolve, it does not change our profession’s overarching goal of helping to reduce the risk of cardiovascular disease worldwide. This requires a concerted effort on behalf of each client to learn how to integrate optimum physical activity, exercise and dietary plans into a sustainable lifestyle.
Realistically, it does not help clients to go on a reduced-saturated-fat dietary regimen if they just replace those fats with other risky foods like refined sugars. As personal trainers, we can help our clients make sensible, evidence-based lifestyle decisions that will improve their quality of life and protect against cardio- vascular disease.
Chowdhury, R., 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., 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. circ.ahajournals.org/content/early/2013/11/11/01.cir.0000437740.48606.d1; accessed June 22, 2014.
Haidich, A.B. 2010. Meta-analysis in medical research, Hippokratia (Suppl. 1), 29-37.
Jakobsen, M.U., 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 (5), 1425-32.
Rizzo, M., & Berneis, K. 2006. Low-density lipoprotein size and cardiovascular risk assessment. Quarterly Journal of Medicine, 99 (1), 1-14.
Siri-Tarino, P.W., et al. 2010. Saturated fatty acids and risk of coronary heart disease: Modulation by replacement nutrients. Current Atherosclerosis Reports, 12 (6), 384-90.