Trans fats – they’re in our chips, bakery goods, popcorn and cakes. We know we should avoid them, but what exactly are they, and why are they so bad for us?

First, let’s take a step back and look at how trans fats fit into the two broad categories of edible fats: saturated and unsaturated.

What are saturated fats?

Saturated fats have a stable chemical composition – they’re solid at room temperature and oxidise slowly. Because they’re very stable and feel good in the mouth, they’re commonly added to processed foods.

Health wise, saturated fats raise the level of cholesterol in the blood. And in large quantities they can increase your risk of heart attacks and strokes.

Animal fats – cream, butter and milk – tend to be at least a half saturated fat. Plant products, such as coconut oil and palm oil, contain saturated fats, as do many prepared foods.

What are unsaturated fats?

The chemical composition of unsaturated fats is much less stable. They’re liquid at room temperature, which makes them more difficult to use.

From a health perspective, they actually lower blood cholesterol.

Fats from most oilseeds, avocado and nuts are unsaturated.

What are trans fats?

Trans fats are variants of unsaturated fats, which have been chemically altered to improve their physical characteristics. They’re produced industrially to harden fats and oils.

Low levels of trans fats are also found naturally in cow fat and milk.

When trans fats were first introduced to food production over 50 years ago, they were considered miraculous because they allowed a liquid oil to be converted to a solid spread without the adverse effects of saturated fat on blood cholesterol.

The original US studies of trans fats didn’t show any elevation of blood cholesterol, so they were thought to be a healthier option.

What makes trans fats harmful?

By the 1990, research by Mensking and Katan showed trans fats elevated the harmful LDL cholesterol by about a tenth more than regular unsaturated fat.

And compared with other fats, trans fats didn’t have the benefit of elevating the protective HDL cholesterol. Mensink and Katan concluded that trans fats were worse for heart disease than the equivalent amount of saturated fat.

This was shown convincingly by Walter Willett in his 1993 study of US nurses. Those who reported eating a large amount of trans fats (more than 5.7 grams a day) were around two-thirds more likely to have a heart attack than nurses eating less than 2.4 grams a day.

Trans fats from dairy and beef fat (“natural” trans) were not linked to heart disease risk.

How are trans fats regulated internationally?

In 2004, Denmark was the first country to ban industrially-produced trans fatty acids at a level of more than 2% of total fat. But it’s too early to tell if this has had an effect on heart disease rates.

The United States took a different approach and mandated the labelling of trans fats on food packaging in 2006. This encouraged manufacturers to question the inclusion of trans fats in their food and many removed the product so they didn’t have to make this declaration.

New York state implemented a partial ban on trans fats in restaurants in 2006, with the ban fully in place in 2008. California and at least a dozen other jurisdictions followed suit, as did Switzerland and Denmark in 2008.

How much trans fats do Australians consume?

Margarines containing trans fats were withdrawn in 1997 and trans fat intake has subsequently declined to a few grams per day.

But even in the 1990s, Australians' intake of trans fat was relatively low, averaging 3.5 grams a day in groups at high risk of heart attacks.

We eat a lot more saturated fat than trans fat.

Do you expect Australia will regulated trans fats?

Several high-fat foods – pies, pasties, sausage rolls, quiches, bagels and donuts – contain more than 4% trans fats.

Although these foods would generally be regarded as unhealthy because of their saturated fat content, it’s important consumers have the option of choosing trans fat-free varieties.

At the very least, trans fats should be labelled so consumers can make their own choice.

Banning trans fats probably isn’t required because labelling would serve the same purpose, but with less administrative burden.

Trans fats are much more harmful to health than saturated fat and should be avoided as much as possible.