What to make of the evidence to support the SFA replacement message

Most dietary guidelines seek to limit intake of saturated fatty acids (SFAs). Human trials show that some SFAs (lauric, myristic, palmitic) raise total-, LDL- and HDL-cholesterol when they isoenergetically replace dietary carbohydrates, with a small elevation in the LDL to HDL ratio. Conversely dietary linoleic acid lowers total- and LDL-cholesterol and lowers the LDL to HDL ratio. A recent systematic review of RCTs of replacement of individual SFAs with unsaturated fatty acids (UFAs) found that total- and LDL-cholesterol were lowered when palmitic acid was replaced with UFAs or oleic acid, but there was no effect on other cardiometabolic risk factors or of replacing stearic acid with UFAs. Several meta-analyses of cohort studies report that intake of SFAs is not associated with risk of cardiovascular disease or coronary heart disease. However, the nature of what SFAs might replace or be replaced with (i.e. carbohydrates or UFAs) differs within and among cohort studies. Some meta-analyses looking at replacement of SFAs with PUFAs or linoleic acid report lowered risk of coronary heart disease. One meta-analysis showed lowered risk of coronary heart disease by replacing SFAs with PUFAs but not with carbohydrates. A meta-analysis of RCTs found that reducing SFA intake lowered risk of cardiovascular events but not of coronary heart disease. Another showed that well-controlled studies found no effect of replacing SFAs with PUFAs. Thus, although effects of some common dietary SFAs on cholesterol and LDL-cholesterol concentrations are clear and are the basis for dietary guidelines, SFAs seem to have limited impact on other cardiometabolic risk factors and have a seemingly modest adverse impact on cardiovascular disease. Factors influencing the impact of SFAs on risk factors and on disease are likely to be the food matrix in which they are provided and the composition of the rest of the diet.