Saturated fatty acids, palm oil and cardiovascular health – where do we stand today?

Abstract

For  almost  sixty years dietary fat  has  been  the  focal  point  for reducing the risk  from  coronary  heart  disease (CHD).  With  evidence  based  largely on  animal  and  observational  studies documenting that  saturated fatty acids (SFA)  increase LDL-C (with the latter being associated with increased CHD risk), the notion that SFA increased CHD, became etched in folklore. As a consequence,   decreasing   SFA   to   <10%   of   total   calories,   became   the corner-stone   of   global   dietary recommendations. Ironically, the fact that SFA increased the large buoyant LDL particles (as opposed to small-dense atherogenic LDL particles), or that they increased the cardio-protective HDL-C and in some instances, lowered the atherogenic Lp(a), went largely unnoticed. However a spate of studies starting in 2009 has dramatically challenged our thinking on the “widely accepted” role of SFA.  Twenty year follow up data from prospective epidemiologic studies suggest that only two classes of fatty acids affect CHD risk, namely trans monounsaturated fatty acids (resulting principally from the partial hydrogenation of vegetable oils) and polyunsaturated fatty acids (PUFA) – which increase and decrease risk, respectively. These studies suggested that when  replacing/removing  SFA   from  the  diet,  the  replacement  nutrient  may  be  as important. Thus SFA replacement with PUFA may provide small benefits, but the replacement represents a dramatic shift in dietary regimen. The effects of replacing SFA with MUFA were inconclusive. If SFA are replaced with carbohydrates, then the quality of the carbohydrate (as measured by the glycemic index) is also important. Earlier this year, a highly publicized study found no benefit on CHD even when SFA were replaced by PUFA, and questioned the usefulness of this public health message. The data on SFA has had a profound effect on the perceived role of palm oil as a dietary constituent. As palm oil contains palmitic and stearic acid (45% and 5% of total fatty acids, respectively), its SFA content was always the focal point for its effects on lipoprotein cholesterol. Several studies have shown that when considering the TC/HDL-C ratio, palm oil produced similar effects as various unsaturated oils (soybean, olive, groundnut and canola). A meta-analysis published earlier this year has confirmed these observations – namely that while palm oil per se may increase LDL-C somewhat in certain instances, it also increases HDL-C. As a result the TC/HLD-C ratio is unaffected. This is particularly so when subjects are consuming ~ 30% of calories from total fat. This talk will provide an overview of the latest studies relating to palm oil /SFA nutrition, with a particular focus on their relevance to the Indian scenario where dyslipidemia, characterized by low HDL-C in 72% of the population, is a major health concern.