Discover the different types of fat in your food.
Fat has a bad reputation. Eating too much has been linked to weight gain, high cholesterol and heart disease, and supermarket packaging nudges us towards the low-fat or fat-free options. But some fat is absolutely essential for survival.
A membrane made from fats surrounds every cell in the human body. Fat insulates our nerve cells, a bit like the plastic coverings on electrical wires. It provides warmth, and it cushions the soles of our feet and the palms of our hands.
Dietary fat also helps us to absorb vitamins A, D and E, which do not dissolve in water. Fats are one of the three macronutrients, the major food types that provide our bodies with energy. The others, carbohydrates and proteins, each provide four kilocalories of energy per gram, but fats pack on a whopping nine kilocalories, making them our densent energy source.
The recommended intake of fat per day is around 95 grams for a man, and 70 grams for a woman, but not all fats have the same effect on our health. While they all provide the same amount of energy, it’s true that some fats are better for our bodies than others.
The main fats in our diet come in the form of fatty acids. These molecules are made from chains of carbon atoms, with a carboxylic acid group at one end. Each carbon in the chain can bind to up to two hydrogen atoms. If all of the carbon atoms are bonded to the maximum number of hydrogen atoms, the fatty acids are ‘saturated’. These fats tend to be solid at room temperature, because the molecules are straight and pack tightly together. Saturated fats come mainly from animals, but can also be found in plant oils like palm and coconut. Eating them has been linked with high cholesterol, so limiting your intake is recommended.
These fats aren’t found in high quantities in nature, and are more commonly made during food manufacturing. The process involves passing hydrogen through unsaturated fats to fill up gaps on the carbon chains. This helps to straighten out molecules, making them behave more like saturated fats. They are solid at room temperature, and have a longer shelf life than their unprocessed counterparts. They are in products like margarine, and in processed foods like cake and biscuits, and are worse than saturated fats for raising blood cholesterol.
Unsaturated fats have gaps in terms of hydrogen atoms bound to their carbon chains. At least two carbon atoms are joined together by a double bond. This creates kinks in the long chains, making it harder for the molecules to pack together. So the fats tend to be liquid at room temperature. Monounsaturated fats have just one double bond. Foods tend to contain a mixture of saturated and unsaturated fatty acids, but the proportions of unsaturated fats are higher in plant foods like olive oil and avocados. They help to lower cholesterol levels in the blood.
Polyunsaturated fats have more than one double bond in their carbon chain, making several kinks. They are found in plant oils, as well as oily fish like mackerel, sardines and salmon. They have been shown to help lower blood cholesterol, and they also have an important role in our cells. Every cell in the body is surrounded by a membrane, which contains fatty acid chains. Polyunsaturated fats are very important in maintaining the fluidity of these membranes, helping to keep them flexible. While we can make many of the fats that our bodies need, some polyunsaturated fats are known as ‘essential’, meaning that we can only get them from our diets.
Omega-3 fatty acids
This group of polyunsaturated fats are mainly found in oily fish, but also in plant foods such as nuts and seeds. They can’t be made by the body, but are important for growth and development, and are thought to have a protective effect on the circulation. Omega-3 fatty acids are found in high concentrations in the brain, and getting enough of these nutrients during childhood is thought to be important for nerve development.
Omega-6 fatty acids
Like omega-3 fatty acids, our bodies cannot make omega-6. These fatty acids are found in meat and vegetable oils, and are often consumed more readily than omega-3. In the US, for example, a typical diet contains over ten times more omega-6 than omega-3. While both are essential for health, researchers think that getting a balance could be important in maintaining optimal health.
Image credits: Wikimedia commons – Lucasmartin2 / Fir0002
Written by the How It Works team
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