And yes, the science is complex and sometimes seems contradictory,
but scientific committees for the past 50 years have concluded one
after another that substituting other kinds of fatty acids for
saturated fatty acids would reduce levels of blood cholesterol and the
risk for coronary heart disease.
And no, those scientists cannot have all been delusional or paid off
by the meat or dairy industries. They--like scientists today--mostly
call the science the way they see it.
What makes the research especially hard to sort out is that all food fats--no exceptions--are mixtures of
saturated, unsaturated, and polyunsaturated fatty acids (just the
proportions differ), that some saturated fatty acids raise blood
cholesterol levels more than others do, and that one kind--stearic
acid--seems neutral with respect to blood cholesterol.
But overall, the vast majority of expert committees typically
conclude that we would reduce our heart disease risks if we kept intake
of saturated fat below 10 percent of total calories, and preferably at or below
7 percent. On average, Americans consume 11 to 12 percent of calories from saturated
fat, which doesn't sound too far off, but the average means that many
people consume much more.
As is often the case with studies of single nutrients, research
sometimes comes to different conclusions. Several studies--all done quite
well--have appeared just in the last year or so.
One of these is a meta-analysis (a review of multiple studies). It concludes:
...there is no significant evidence for concluding that
dietary saturated fat is associated with an increased risk of CHD
[coronary heart disease] or CVD [cardiovascular disease]. More data are
needed to elucidate whether CVD risks are likely to be influenced by
the specific nutrients used to replace saturated fat [my emphasis].
What saturated fat gets replaced with is the subject of three other
well-conducted studies that come to a different--the
mainstream--conclusion. One, another recent meta-analysis, confirms decades of previous observations (sorry about the annoying abbreviations):
These findings provide evidence that consuming PUFA
[polyunsaturated fatty acids] in place of SFA [saturated fatty acids]
reduces CHD events in RCTs [randomized clinical trials]. This suggests
that rather than trying to lower PUFA consumption, a shift toward
greater population PUFA consumption in place of SFA would significantly
reduce rates of CHD.
Translation: replacing saturated fats with polyunsaturated fats would be healthier.
Another meta-analysis comes to the same conclusion:
The associations suggest that replacing SFAs with PUFAs
rather than MUFAs [monounsaturated fatty acids] or carbohydrates
prevents CHD over a wide range of intakes.
A very recent consensus statement concludes:
the evidence from epidemiologic, clinical, and
mechanistic studies is consistent in finding that the risk of CHD is
reduced when SFAs are replaced with polyunsaturated fatty acids
(PUFAs). In populations who consume a Western diet, the replacement of
1% of energy from SFAs with PUFAs lowers LDL cholesterol [the "bad"
kind] and is likely to produce a reduction in CHD incidence of ≥2-3%.
No clear benefit of substituting carbohydrates for SFAs has been shown,
although there might be a benefit if the carbohydrate is unrefined and
has a low glycemic index.
The advisory committee to the 2010 Dietary Guidelines for Americans reviewed this and other research relating saturated fatty acids to heart disease risk and concluded:
Cholesterol-raising SFAs, considered SFA minus stearic
acid...down-regulate the low density lipoprotein (LDL) receptor by
increasing intracellular cholesterol pools and decreasing LDL
cholesterol uptake by the liver.
The committee's research review addressed the question, "What is the
Effect of Saturated Fat Intake on Increased Risk of Cardiovascular
Disease or Type 2 Diabetes, Including Effects on Intermediate Markers
such as Serum Lipid and Lipoprotein Levels?" It judged the evidence strong
that intake of dietary SFA is positively associated with
intermediate markers and end point health outcomes for two distinct
1) increased serum total and LDL cholesterol and increased risk of CVD and
2) increased markers of insulin resistance and increased risk of T2D
[type-2 diabetes]. Conversely, decreased SFA intake improves measures
of both CVD and T2D risk.
The evidence shows that 5 percent energy decrease in SFA, replaced
by MUFA or PUFA, decreases risk of CVD and T2D in healthy adults and
improves insulin responsiveness in insulin resistant and T2D
How much saturated fat might increase the risk of heart disease or
type-2 diabetes depends on how much you eat as well as what you eat.