Why is fat demonised?
The bad reputation of fats, saturated fats in particular, dates back to the 1950s when researchers proposed the lipid hypothesis: a theory that dietary fat raises cholesterol and increases the risk of heart disease. This hypothesis evolved to single out saturated fats as the culprit. In conjunction with an increasing focus on the link between calories and weight gain, this has led to an ingrained and undiscriminating fear of dietary fat.
Why do we need fat?
Fats are vital to processes throughout the body: nervous system development, immunity, metabolism, hormone balance, inflammation control, joint health, brain function, cholesterol control and much more. Some of the required fats are “essential”, meaning that they can’t be made by our bodies directly and must therefore be consumed through our diets.
Types of fat?
There are 3 principal categories of fats; saturated, unsaturated and trans. Fats are classified according to their chemical structure, specifically by how tightly packed the component fatty acids are. Saturated fats (red meat, dairy, coconut oil) have a compact structure, making them solid at room temperature. Unsaturated fats, generally considered the healthiest type, can be either monounsaturated (olive oil, avocados, most nuts) or polyunsaturated (fatty fish, flaxseeds, vegetable oils), with the latter having the least tightly packed structure. Trans fats (margarine, commercial fried foods, processed snack foods) are formed when liquid vegetable oils are processed to give them a solid structure and prevent them from becoming rancid.
1 - Saturated fats
Decades of dietary advice has warned of the harmful effects of saturated fat through an increased risk of heart disease. However, more recent studies have cast doubts over this linkage. Furthermore, various types of saturated fats play key roles in the body:
· Essential for nervous system development and structurally vital for the brain.
· Cardiovascular health relies on small amount of saturated fats.
· Involved in immunity.
· Needed to synthesise steroid hormones (testosterone, oestrogen and progesterone).
· Necessary for cell membrane construction.
· Required for absorption of fat-soluble vitamins A, D, E and K.
However, there are still some clear drawbacks to saturated fats which mean that we must remain vigilant of over-consumption:
· Can increase the risk of inflammation, which can cause issues with cardiovascular health, immunity, diabetes and more.
· Can increase levels of bad (LDL) cholesterol.
· Some types (such as those in red meat) strain the digestive system.
· Can compete for absorption with healthy fats such as omega-3 and omega-6.
2 - Unsaturated fats
Olive oil is perhaps the best known source of monounsaturated fat and boasts many health benefits, especially for cardiovascular health. Other good sources include various other oils (peanut, canola, sunflower), avocados and most nuts and seeds. Monounsaturated fats support healthy cholesterol levels and aren’t as inflammatory as saturated fats.
These are “essential” fats, meaning that our bodies need them but can’t self-produce them. There are 2 main types: omega-3 fatty acids and omega-6 fatty acids. Omega-3 fatty acids help balance cholesterol levels, play a structural role in the brain, are involved in memory, concentration and alertness, have anti-inflammatory properties and are antioxidants. Good sources include fatty fish (salmon, mackerel, sardines), flaxseeds and walnuts. Omega-6 fatty acids, such as vegetable oils, are immune supporting. However, they can also cause inflammation, so a delicate balance of omega-3 to omega-6 is required; too much vegetable oil from popular processed foods can disrupt this. Also note that cheaper vegetable oils (including those higher in monounsaturated fats) are often heavily processed using bleach, caustic soda and other chemicals which, amongst other issues, could negate their antioxidant properties.
3 – Trans fats
Although small amounts of trans fats can be found naturally in animals (these are thought to be less harmful and may offer some nutritional benefit), they are predominantly artificial and found in processed foods. Our bodies struggle to recognise the chemical structure of these fats. They also encourage bad LDL cholesterol, can damage cells (blood vessels in the brain in particular), compete with healthy fats for absorption and are highly inflammatory, which in turn is thought to increase the risk of diabetes, heart disease and other chronic conditions.
Cooking with fats
When fats are heated, they oxidise which causes their structure to alter and can result in the production of toxic aldehydes. Aldehydes have been linked to various health issues, including heart disease, dementia and cancer. The level of degradation and aldehyde formation varies according to the fat type.
Saturated fats, with their compact structure, are more likely to remain stable when heated. Monounsaturated fats, which are slightly less tightly packed, are generally also quite resistant to heat degradation. Polyunsaturated fats (including olive oil and other vegetable oils) are far less resilient. Vegetable oils can also form harmful trans fats when heated to temperatures of around 150°C, well below the levels reached in deep frying. Coconut oil, butter, ghee, lard, macadamia and avocado oil have a higher saturated and monounsaturated acid content, and are therefore safer to use for cooking. Olive oil is high in monounsaturated fats (76%) and contains some saturated fats (14%), and is therefore safer than many other vegetable oils, although much of the benefits associated with olive oil are lost when it reaches high temperatures. Also, be sure to store your cooking fats in a cool, dry and dark environment to limit oxidation, which is caused by heat, oxygen and light.
· Don’t fear fat! Healthy fats are essential to vital bodily functions.
· Make room in your diet for good fats, even if you’re trying to lose weight.
· Avoid “low-fat” products if they are loaded with refined sugars and artificial ingredients to replace the removed fat.
· Avoid trans fats completely.
· Prioritise polyunsaturated and monounsaturated fats instead.
· Try to get a good source of omega-3 fatty acids (e.g. oily fish) at least 3-4 times per week.
· Be careful of vegetable oils which are heavily processed and have lost their natural health benefits.
· The historical bad reputation of saturated fats may not be entirely warranted. Don’t eliminate altogether; some healthy sources in moderation can do you good.
· The structure and beneficial properties of fats change when they are heated, so choose cooking oils carefully. Use more stable saturated and monounsaturated fats for cooking and try to avoid vegetable oils.