Attack of the killer margarine: the reboot

In 2015, the Herald had a story from the Daily Telegraph on the alleged risks of margarine:

Saturated fat found in butter, meat or cream is unlikely to kill you, but margarine just might, new research suggests.

Traditionally people have been advised to reduce animal fats, but the biggest ever study has shown they do not increase the risk of stroke, heart disease or diabetes. However, trans fats, found in processed foods such as margarine, raise the risk of death by 34 per cent in less than a decade.

“For years everyone has been advised to cut out fats,” said study lead author Doctor Russell de Souza, an assistant professor in the Department of Clinical Epidemiology and Biostatistics, at McMaster University in Canada.

It’s a bit unclear exactly what “raise the risk of death by 34 per cent in less than a decade” is supposed to mean, but we’ll get to that. The research paper was in the BMJ, and came out on the same day the story did.

Today, in 2017, the Herald had a story from the Daily Telegraph on the alleged risks of margarine:

Saturated fat found in butter, meat or cream is unlikely to kill you, but margarine just might, new research suggests.

Although traditionally dieticians have advised people to cut down on animal fats, the biggest ever study has shown that it does not increase the risk of stroke, heart disease or diabetes.

However trans-fats, found in processed foods like margarine raises the risk of death by 34 per cent.

“For years everyone has been advised to cut out fats,” said study lead author Doctor Russell de Souza, an assistant professor in the Department of Clinical Epidemiology and Biostatistics, at McMaster University in Canada.

It’s a bit unclear exactly what “raise the risk of death by 34 per cent in less than a decade” is supposed to mean, but we’ll get to that. The research paper was in the BMJ, and came out nearly two years before the story did.

Yes, it really seems to be the same ‘new reasearch’: Dr de Souza hasn’t just published another meta-analysis. It even seems to be the same Telegraph story; I couldn’t find a new one.

So, how scared should we be of trans fats in our diets?  Food Standards Australia New Zealand say

Monitoring of TFAs in the Australian and New Zealand food supply has found that Australians obtain on average 0.5 per cent of their daily energy intake from TFAs and New Zealanders on average 0.6 per cent. This is well below the WHO recommendation of no more than 1 per cent.

They also say that the majority of that 0.6% is made by bacteria in the rumens of cows and sheep, not by industrial hydrogenation; the evidence of harm is weaker for these natural trans fats.

Now, back to the 34% statistic. This is based on two studies. One compared the 20% of people with the highest and lowest trans fat intakes and found a rate ratio of 1.24. The other, smaller, one estimated the ratio as 1.71 between the highest and lowest 25%.   These are rate ratios estimated from people in their 60. Since the actual probability of death in any given year would have been about 1% the absolute risk increase is smaller than “34% in less than a decade” sounds — but not at all trivial.  For comparison, the all-cause mortality rate ratio for current smoking is about 3.0, or 200% higher than non-smokers.

More importantly, though, we’re talking about a lot of trans fat in these studies. In the larger study with the less-scary rate ratio, people in the lowest 20% of trans fat intake got an average of 1.6% of their calories from it. That is, the lowest-risk group were eating three times as much trans fat as an average Kiwi today.  In the smaller study, they don’t give actual trans fat information for the groups they are comparing, but the average for the whole study was about 9% of fat in the blood was trans fat: if that even roughly translates to proportions of dietary fat they were also getting more than the typical Kiwi today.

There just isn’t that much trans fat in most margarine any more, less than 1% on average (according to Food Standards Oz/NZ, table 2) . There used to be a lot, but then we found out it’s bad for you.  Those scary numbers are actually good news if they’re true: they’d measure how much better off margarine consumers are today than twenty years ago.

(via Mark Hanna)