Perceptions concerning the benefits and function of fats and fatty acids in human nutrition have gone through a series of rather dramatic changes over the past several years. Not too long ago, fats of all types were reviled by the consuming public as witnessed by the numerous low-fat and no-fat diets that were once in vogue. More recently, the pendulum has swung the other way, as high fat and high protein diets became the rage. Today, the tendency is to moderate our total fat intake, focusing our attention on increasing intake of monounsaturates and omega-3 (n-3) oils, while reducing or eliminating saturates, trans- fats and omega-6’s (n-6) from our diets.
While consumer understanding of the roles of fats and fatty acids in our diet is improving, the mass media’s tendency to over simplify and gloss over complex issues continues to result in misconceptions and misperceptions. Among these misconceptions is a general belief that n-3 fatty acids from plant based sources are not as “bioavailable” or “efficacious” as marine and algae based n-3 fatty acids.
Plant based alpha-linolenic acid (ALA) is an essential fatty acid. It is the precursor of the long-chain polyunsaturated fatty acids (PUFA) of which eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are two well-known members with recognized roles in human physiology.
There are landmark studies that support the beneficial effects of ALA especially related to heart health. The Cardiovascular Heart Study is a large prospective cohort study of elderly Americans. Starting in 1989, and continuing through 1999, participants underwent annual extensive clinical examinations. Measurements included traditional risk factors such as blood pressure and lipids as well as measures of subclinical disease, including echocardiography of the heart, carotid ultrasound, and cranial magnetic-resonance imaging (MRI). At six month intervals between clinic visits, and once clinic visits ended, participants were contacted by phone to ascertain hospitalizations and health status. In that study, significant associations existed between a higher dietary intake of alpha-linolenic acid (ALA) and a decreased risk of total and non-cardiovascular mortality (1).
A further approach to better understand the possible importance of ALA in the diet is through experimental intervention under controlled conditions. Egert and colleagues have undertaken a controlled exercise and dietary intervention study (2). In this research, a group of overweight-to-obese patients with metabolic syndrome received a 6-month weight-loss intervention. Half of the study participants received a hypo-energetic diet containing a low daily content of 0.9 g ALA, and the other half the same diet with a high daily content of 3.4 g ALA.
Both groups of participants lost weight and body fat mass, experienced a reduction in blood pressure, and displayed significant reductions in a range of circulatory markers of inflammation (C-reactive protein, TNF-α, IL-6, sVCAM-1, sICAM-1 and E-selectin), and markers of endothelial function (endothelin, asymmetric dimethyl-arginine).
Of interest, whereas the weight-loss intervention was successful, no significant differences were seen for any of these markers between the two study groups except for one protein, YKL-40. This glycoprotein is considered a mediator of inflammation and is secreted by macrophages. It is formed upon damage of the vascular endothelium (interior surface of blood vessels and lymphatic vessels). Serum YKL-40 levels decreased significantly faster in those participants who received a higher dose of ALA in their diet during the course of study. It will be interesting to learn from further studies if the effect on YKL-40 is specific to ALA, or whether the effect is mediated via further transformation to EPA/DHA.
References:
1. Fretts AM, Mozaffarian D, Siscovick DS, Sitlani C, Psaty BM, Rimm 3EB, Song X, McKnight B, Spiegelman D, King IB, Lemaitre RN. Plasma phospholipid and dietary α-linolenic acid, mortality, CHD and stroke: the Cardiovascular Health Study. Br. J. Nutr. 2014;112(7):1206-1213. [PubMed]
2. Egert S, Baxheinrich A, Lee-Barkey YH, Tschoepe D, Wahrburg U, Stratmann B. Effects of an energy-restricted diet rich in plant-derived α-linolenic acid on systemic inflammation and endothelial function in overweight-to-obese patients with metabolic syndrome traits. Br. J. Nutr. 2014;112(8):1315-1322. [PubMed]