Trans, poly, mono and hydrogenated: a fat-finding mission

Bad news is that we’re still eating too much saturated fat as part of our overall fat intake

All fats are equal when it comes to the amount of calories they provide, but they’re far from equal in their effects on our bodies. So although fat is an essential food we need to eat, it’s worth making healthy and not harmful choices. Recent changes to food labelling mean that has now become easier for consumers.

The main types are saturated and unsaturated. Monounsaturates and polyunsaturates both lower the “bad” LDL cholesterol. Saturated fats raise LDL, which we don’t need because of its known role in heart disease.

There are also transfats, of which some occur naturally but most are manufactured by passing hydrogen atoms through a liquid vegetable oil to render them a more useful solid fat for food manufacturers. These both raise LDL and lower the “good” HDL cholesterol, a double whammy none of us wants. Denmark has banned industrially produced transfats.

The good news is that transfats are being phased out by the food industry. But partially hydrogenated fats may contain some transfats, according to Dr Mary Flynn, chief specialist in public health nutrition at the Food Safety Authority of Ireland (FSAI). Since December 2014, under EU law, manufacturers can no longer use the innocent-sounding "vegetable oil" but have to specify which vegetable oil or oils they're using in a product and also state whether partially or fully hydrogenated fat is used. Fully hydrogenated fat is saturated, and the amount will be on the label.


As a nation with one-third of deaths caused by heart disease, the bad news is that we’re still eating too much saturated fat as part of our overall fat intake. The advice on saturates is to limit them to not more than 10 per cent of one’s daily calories, or 20g per day for the average woman and 30g for the average man. Much of our saturated fat comes from foods such as meat and dairy, which supply essential nutrients such as iron and calcium, which many people in this country are not getting enough of.

Vegetable fats

Just because a fat comes from a vegetable doesn’t mean it’s healthy. Some common vegetable fats often found in processed foods are highly saturated, even more so than butter. Coconut oil, for example, much promoted now and displayed in supermarkets, is 87g of saturated fat per 100g compared with butter at 52g. Dr Cliodhna Foley-Nolan, director of human health at Safefood, says “there are no scientifically accepted health claims” for it. And what is often used in a range of processed foods is palm oil ,which is 48g saturated fat per 100g.

As the FSAI has found, if you keep a record of how much saturates you eat in a typical day’s eating you’ll find that it’s not as easy as it might seem trying to keep to the limit of 20g or 30g, even using lean meat and low-fat dairy. Processed foods increase the amount greatly. One quarter of a popular frozen pizza has 5g saturated fat, while a 53g bar of chocolate has 9.8g. As a guide, under 1.5g of saturates per 100g of a food is considered low, between 1.5g and 5g is medium and more than 5g per 100g is high.

The body needs some “essential fatty acids” that it can’t make. The best source for one of these, omega 3, is oily fish such as salmon and mackerel. The omega 3 found in plant sources is different from that in fish.

It hasn’t yet been established how much omega 3 plant sources one would need to eat to obtain enough of this fatty acid. Plant-based supplements “are not a good source of omega 3”, says the Irish Nutrition and Dietetic Institute (INDI), but fish oil supplements can supply the omega 3 needed (see

We don’t need to obsess about fats, says Foley-Nolan, but a few rules of thumb can help, such as using oils by the teaspoonful to keep control of the amount you use, or remembering that a 7g wrapped pat of butter is enough to cover two slices of bread.

The best advice is to have a varied diet and to reduce all types of fat, says Flynn. Sugar offers four calories per gram compared with the nine calories per gram of fat. Drizzling oil over foods she describes as “madness”. Butter needs to be seen as a “pleasure” only, and if spreads are used regularly it’s better to use a mono or polyunsaturated spread instead.

To retain moisture during cooking, Flynn suggests using a teaspoon of oil in a nonstick pan and adding a little extra water if necessary.

Cliodhna McDonough, clinical dietician manager at St Columcille’s Hospital in Loughlinstown, Co Dublin, and spokeswoman for the INDI, says high heat can damage the nutritional value of oils, especially when heated beyond their “smoking point”; this varies from one oil to the next. This can result in dangerous compounds being released into food.

McDonough says Department of Health guidelines still remain that olive oil is the best for cooking purposes as it contains more of the oils that resist oxidisation. Ideally, though, we all need to be frying less, and at lower temperatures.