Stewart Truswell: Fat facts

A SYSTEMATIC review published last month created a bit of a storm as to whether recommendations to reduce saturated fat in our diet were based on evidence.

The article, in Open Heart, claimed that no randomised controlled trial (RCT) had tested government recommendations to reduce saturated fat intake before they were introduced in 1977 in the US and in 1983 in the UK to help prevent coronary heart disease (CHD).

The paper stimulated an article in The Guardian with the alarming subtitle “Researchers claim dietary advice around fat consumption, followed by millions for the past 30 years, should never have been issued”.

Neither the Open Heart paper nor The Guardian article asks whether today’s diet/heart advice is in error.

RCTs are, of course, the ultimate test for pharmaceuticals. Patients are randomly given either the test drug or a placebo with no biological action. Compliance can be checked by measuring the drug in blood samples.

However, for nutrition research this is not usually possible. If a test food is added or removed, some other food must replace it to keep the calorie intake level, and compliance is hard to maintain and assess.

RCTs of dietary change are uncommon except for trials with pure micronutrients.

When reduced saturated fat has been researched in controlled human trials it has usually been replaced with foods containing polyunsaturated fat [PUF]. These diet trials tested the combined effect of removing saturated fat and adding PUF.

All these trials were completed between 1966 and 1989, before statins were available to lower plasma cholesterol.

Meta-analyses published in more recent times find that the combination of reduced saturated fat and increased PUF does lead to significantly fewer CHD events.

The low density lipoprotein (LDL)-cholesterol-raising effect of saturated fatty acids had been first reported in The Lancet in 1957.

Expert committees first recommended reducing saturated fat intake to prevent CHD in 1961 in the US and in 1976 in the UK, following a report of a joint working party of the Royal College of Physicians of London and the British Cardiac Society. These recommendations were then taken up by the governments of both countries and later in Australia.

When the committees which developed these recommendations in the US and the UK met they had other information available showing ecological CHD was common in communities with higher plasma cholesterols; prospective studies, including the Framingham study, showing people with high plasma cholesterols had more CHD events in the next 10 years; and RCT results consistent with benefits from reducing saturated fat and increasing PUF.

Lowering plasma LDL-cholesterol has been a major way to deal with the CHD epidemic. Age-standardised death rates from CHD started to come down rapidly 7 years after the dietary recommendations were first introduced in the US in 1961 and 7 years after the 1976 recommendation in the UK.

In 1995 statins were introduced and the mortality decline has continued.

There has been a vast amount of literature in the past 50-plus years that does not support the claims made in the Open Heart articles.

Advice to limit intake of saturated fat should continue.
 

Professor Stewart Truswell is emeritus professor of human nutrition at the University of Sydney.

COI: Professor Truswell was a member of the Royal College of Physicians committee in 1976 and wrote an editorial for The BMJ in 1984 about the UK Department of Health and Social Security’s report that followed the dietary advice of the Royal College of Physicians.