Fats: the helpful and the harmful
Learn why you need fat, how saturated, unsaturated and trans fats differ, and which swaps guidelines recommend.
WHY YOU NEED IT
Three jobs fat does
- Stores energy. At about 9 kcal per gram, fat is the densest fuel in food (lesson 1).
- Builds cells. Every cell in your body is wrapped in a membrane made largely of fat.
- Carries vitamins. Vitamins A, D, E and K are fat-soluble: they need some fat in the meal to be absorbed.
A salad of carrots and greens with a spoon of olive oil lets you absorb more of the vitamin A the carrots provide than the same salad with no fat at all.
Check yourself
Which vitamins need some fat in the meal to be absorbed well?
- B and C
- A, D, E and K
- Only vitamin C
- All vitamins equally
Show the answer
A, D, E and K
Right. A, D, E and K are fat-soluble, so a little fat in the meal helps you absorb them.
A quick rule of thumb: liquid or solid?
Mostly saturated · solid at room temperature
Butter, ghee, animal fat, fatty and processed meat, cheese, cream, and also coconut and palm oil. WHO advises keeping saturated fat below 10 % of daily energy, about 22 g on 2,000 kcal.
Mostly unsaturated · liquid at room temperature
Olive, canola (rapeseed) and sunflower oils, nuts, seeds, avocado and oily fish. Replacing saturated fat with these is linked to lower LDL ("bad") cholesterol and a lower risk of heart disease.
Check yourself
Sort these by the kind of fat they mostly contain.
- Olive oil
- Ghee
- Walnuts
- Butter
- Sardines
- Coconut oil
- Sunflower oil
- Palm oil
Show the answer
Mostly unsaturated: Olive oil, Walnuts, Sardines, Sunflower oil
Mostly saturated: Ghee, Butter, Coconut oil, Palm oil
Industrial trans fat
Fat made in a factory by partially hydrogenating vegetable oil, to turn it solid and keep it longer. It has been used in some margarines, shortening, and fried and baked snacks. Trans fat raises LDL and lowers HDL ("good") cholesterol, a double hit. WHO advises keeping it below 1 % of energy and has called for it to be removed from the food supply altogether.
On an ingredients list, the words "partially hydrogenated" oil or fat are the sign. Iran and many other countries now regulate trans fat, but it's still worth a glance at the label.
WHO limits, turned into grams on a 2,000 kcal day
(fat has about 9 kcal per gram)
total fat about 30 % 600 kcal / 9
saturated fat under 10 % 200 kcal / 9
trans fat under 1 % 20 kcal / 9total fat about 67 g at most
saturated fat under about 22 g
trans fat under about 2 gThese are rough ceilings for an average day, not targets to fill. On a smaller or larger energy intake the grams scale with it.
Check yourself
What does WHO advise as the limit for saturated fat?
- Under 1 % of daily energy
- Under 10 % of daily energy
- Under 50 % of daily energy
- No limit, as long as it's natural
Show the answer
Under 10 % of daily energy
Right. Under 10 % of daily energy, which is about 22 g on a 2,000 kcal day.
Check yourself
Hamid is checking the ingredients on a packet of biscuits. Which phrase tells him it contains industrial trans fat?
- "Cold-pressed"
- "Partially hydrogenated vegetable oil"
- "High in omega-3"
- "Made with sunflower oil"
Show the answer
"Partially hydrogenated vegetable oil"
Yes. Partial hydrogenation is the process that makes industrial trans fat, so that phrase is the giveaway.
Omega-3 fats
A family of unsaturated fats the body needs but can't make enough of on its own. The richest sources are oily fish such as salmon, sardines, mackerel and trout; walnuts and flaxseed provide a plant form. UK advice is two portions of fish a week, one of them oily.
A tin of sardines on bread counts as a portion of oily fish, and it's one of the cheaper ways to get there.
Four easy swaps
- Cook with a liquid oil
Use olive, canola or sunflower oil in place of ghee, butter or solid cooking fat for everyday dishes.
- Measure with a spoon
Pour the oil into a spoon, not straight from the bottle. Two spoons for a pot of stew is often plenty.
- Swap the pastry for nuts
A handful of unsalted nuts or seeds instead of a pastry or biscuits trades mostly saturated fat for mostly unsaturated.
- Put fish on the menu twice a week
One portion oily, such as sardines, mackerel or salmon. Grilled or baked keeps it simple.
Check yourself
Coconut oil comes from a plant, so it's mostly unsaturated like olive oil.
Show the answer
False
False. Coconut oil is one of the few plant oils that is mostly saturated, which is why it's solid in a cool kitchen. Palm oil is high in saturated fat too. "Plant" doesn't guarantee unsaturated: the liquid-or-solid rule is a better guide.
Lesson recap
- You need fat: it stores energy, builds cells and carries vitamins A, D, E and K.
- Mostly unsaturated fats (liquid oils, nuts, seeds, oily fish) are the ones to lean on; replacing saturated fat with them is linked to lower heart-disease risk.
- Mostly saturated fats (butter, ghee, fatty meat, coconut and palm oil): WHO advises under 10 % of energy, about 22 g on 2,000 kcal.
- Industrial trans fat: under 1 % of energy, and ideally none. Look for "partially hydrogenated" on the label.
- Two portions of fish a week, one oily, and simple swaps like measuring oil with a spoon go a long way.