The conventional wisdom that saturated fats are problematic for human nutrition is simply not credible any more, in the face of increasing scientific evidence. The latest evidence comes from De Souza et al, who have published in the British Medical Journal (http://www.bmj.com/content/351/bmj.h3978) looking into saturated fat consumption. I will examine the scientific details in this blogpost – but the important headline is that we, as medical professionals, media, society, need to challenge the previously assumed link between saturated fats and CVD. The evidence now shows that the old advice was wrong.
Palm oil is one saturated fat that has suffered from this misperception: my hope is that the more evidence emerges, the more difficult it will be for anti-palm oil activists to persist with their erroneous negative claims.
Saturated fat consumption, scientific interest and political issues
Fat consumption has been scrutinised by researchers and government agencies since the aftermath of World War 2. This is mainly the consequence of the lipid heart hypothesis formulated by the scientist Ancel Keys, in the 1950s, which was never confirmed but has passed into dietary guidance ever since. This study suffered all the bias of retrospective or prospective non-interventional epidemiological studies about diet and CVD. Particular weaknesses include –
- Very poor quality of diet analysis and questionnaires
- No control group and a lot of confounding parameters
- Weak correlations and very low absolute risk differences
- Wide range of metabolic responses among individuals to intake of carbs / lipids / proteins
- Ignorance of the type of fat and especially the amount of industrially produced trans fats
- Selection of countries and/ or avoidance of those with high intake of saturated fats and low CVD rates like France or Spain.
To illustrate this, let me review the selection process of the studies as shown in Figure 1 of the paper (http://www.bmj.com/content/351/bmj.h3978). THE BMJ paper finds that os much of the literature on saturated fats following Ancel Keys was not of sufficient scientific quality. From 20,413 studies in the database, only 41 were selected (because of lack of information, low quality, and other insufficiencies). For instance, from the 445 studies resulting of a process of eligibility based on the full text, 372 were excluded because:
- They did not assess saturated fat exposure
- They did not measure outcomes of interest
- They duplicate data from previous publications
- They did not present a measure of associations
- They have an inappropriate study design.
There is more, the GRADE (http://www.gradeworkinggroup.org/index.htm) evidence profile of quality is very low for all the comparisons done in the selected studies in the past around saturated fats, as found yb the BMJ (http://www.bmj.com/content/bmj/suppl/2015/08/11/bmj.h3978.DC1/sour025275.ww5_default.pdf).
What are the findings?
Once more, I have to insist on a critical point in human observational studies about diet: mortality is crucial. Without any effect on mortality, observational studies should be taken with extreme precautions for further conclusions. Figure 2, which is displayed below, illustrates very precisely how saturated fat are neutral on different risks and the great heterogeneity of studies on CHD and saturated fats.
Recently the number of papers by nutrition specialists who doubt or challenge results of studies about saturated fats and CVD has increased because the statistical reality as assessed by meta-analysis or recalculating old data is indeed against any detrimental effect of saturated fats on cardiovascular health.
Atheroma and CVD are complex issues, which are not caused by fat (or cholesterol) in your plate, and therefore not caused by palm oil.
Without a doubt, we are near the end of a myth. The only surprise is the slowness of the process i.e. the extraordinary conservatism of the scientific community about the diet heart hypothesis. No doubt that economic interests (the low-fat industry, the sugar industry and at large the agro-food industry) and the traditional reluctance to change of highly centralised bureaucracy are key explanations for exceptional lasting of this myth. But enough is enough because this advice is not neutral and even deleterious to populations following it and consequently do not engage in actual and efficient prevention of CVD.