Dietary Fats: Types, Roles and Food Sources

What fat does in the body

Fat is one of the three macronutrients. It provides energy and supplies essential fatty acids that the body cannot make itself. Fat also helps the body absorb the fat-soluble vitamins A, D, E and K (covered in Lesson 6), and fats are part of the structure of every cell.

Fat and energy

Fat provides about 9 kcal per gram, more than twice as much as carbohydrate or protein (about 4 kcal per gram each). That's why foods high in fat, such as oils, butter and nuts, are energy-dense even in small amounts. See Lesson 2 for how energy is calculated.

The main types of fat

Fats are made of fatty acids, which are grouped by their chemical structure:

UK NHS guidance, for example, advises cutting down on saturated fat and choosing foods with more unsaturated fat instead, as part of an overall healthy diet. Advice on fat differs in detail between countries, so it's worth checking guidance where you live.

Omega-3 and omega-6

Omega-3 and omega-6 are families of polyunsaturated fatty acids. Some of them are essential, meaning they must come from food. Omega-6 fats are found in many vegetable oils, nuts and seeds. Omega-3 fats are found in oily fish (such as salmon, mackerel and sardines) and, in a different form, in some plant foods such as walnuts, flaxseed and rapeseed oil.

Research on omega-3s is ongoing, and this course doesn't make claims about them treating or preventing specific conditions. UK guidance, for example, recommends eating fish regularly, including oily fish, as part of a healthy diet.

Trans fats

Trans fats occur naturally in small amounts in some meat and dairy foods. Industrially produced trans fats come mainly from partially hydrogenated oils, which were used in some processed foods. The WHO advises limiting trans fat intake, and regulators in several places, including the US and the EU, have taken steps to limit industrially produced trans fats in food. Rules and timelines differ between countries, so check the sources below and guidance where you live.

Foods contain a mix of fats

It's tempting to sort fats into “good” and “bad”, but real foods contain a mixture of fatty acids. Olive oil contains some saturated fat; butter contains some unsaturated fat. Foods also differ in everything else they provide. Looking at your overall diet is more useful than labelling single foods.

Reading fat on a label

UK and EU labels show fat with of which saturates underneath. US Nutrition Facts labels show Total Fat with Saturated Fat and Trans Fat listed beneath it. Some products voluntarily list mono- and polyunsaturated fats too.