A recent editorial in the journal Open Heart suggests many of us have it all wrong when it comes to the balance of fats we eat.
The authors urge a return to equal amounts of specific types of fats known as omega-6 and omega-3 polyunsaturated fatty acids in order to help combat global obesity.
The paper reflects a recent wave of evidence supporting a revision of guidelines around dietary fat, including in Australia.
Fats - more correctly referred to as fatty acids - are a major dietary source of energy, along with carbohydrate and protein. Fats can be saturated or unsaturated, terms that refer to the makeup and structure of the fat molecules.
Polyunsaturated fatty acids include the groups of omega-6 and omega-3 fats. The omega-6 linoleic acid and omega-3 alpha-linolenic acid are called essential fats, as humans cannot produce them: we need to obtain these from dietary sources.
Major sources of omega-6 polyunsaturated fatty acids are seeds that are used abundantly in vegetable oils like safflower and sunflower oil. These oils are commonly used to make margarines. Processed foods such as cakes, biscuits, burgers, pizza and chips are therefore high in omega-6.
Plant sources of omega-3 alpha-linolenic acid are nuts (such as walnuts), seeds (such as linseeds) and green leafy vegetables. The longer chain, more highly unsaturated omega-3s known as eicosapentaenoic acid and docosahexaenoic acid come from algae and oily fish like salmon, tuna, mackerel and sardines.
There is good evidence for the health benefits of monounsaturated fatty acids: these are found in olive oil, macadamia oil, avocado, and selected nuts like almonds and peanuts.
Highly processed food also contains trans fatty acids which occur as a result of the hydrogenation of vegetable oils for margarine, commercial cooking and manufacturing. This process alters the structure of the fat, and these are associated with increased risk of heart disease.
Apart from contributing energy that our bodies need to work properly, fats have numerous important health benefits including healthy skin and hair, absorbing fat-soluble vitamins (A, D, E and K), and insulation to keep us warm.
Omega-3 and omega-6 polyunsaturated fatty acids are important for brain development. Docosahexaenoic acid is particularly concentrated in our brains, where it has multiple important roles in healthy brain function, cognition and mental health.
Furthermore, omega-3 polyunsaturated fatty acids produce important chemicals that reduce inflammation and blood clotting, and improve blood vessel dilation. Conversely, omega-6 polyunsaturated fatty acids promote inflammation, clotting and constriction of blood vessels.
A diet low in omega-3 and rich in omega-6 can therefore create a range of problems, including chronic inflammation and poor blood flow. These changes are associated with chronic diseases such as obesity, heart disease, stroke, mental illness and dementia.
In traditional societies, humans consumed a ratio of roughly 2-1:1 of omega-6 to omega-3 polyunsaturated fatty acids. This came about due to diets rich in fish, plant foods and free grazing animals, and eggs from chickens that ate plants high in omega-3 fats.
In industrialised regions such as Europe and the United States, the dietary ratio of omega-6 to omega-3 is very different, being closer to 16:1. In Australia it is estimated to be 8:1.