There is a lot of conflicting information and disagreement about fats - even among experts. But just WTF is fat and is it going to kill you? Read on to learn the science behind fats, the different types of fats, and what differentiates a killer fat from life-enhancing fat.
The Science of Fat
There are three basic kinds of fat molecules consumed by humans; these are Saturated Fatty Acids (SFA), Monounsaturated Fatty Acids (MUFA), and Polyunsaturated Fatty Acids (PUFA). There are two main characteristics that differentiate fatty acid molecules: the first is the number of hydrogen bonds in the molecule and the second is the chain length of the molecule.
Hydrogen Atom Variance
The chain length of a fat molecule can vary (how many carbon atoms), as well as the total number of hydrogen atoms bonded to each carbon atom in the chain. It is this variance that gives each type of fat its specific characteristics.
In an SFA molecule, every carbon atom has two hydrogen atoms bonded to them – the carbon atoms are ‘saturated’ with hydrogen – giving the molecule a structure that is straight and where the atoms are strongly bonded together. This is why saturated fats have a high melting point and why they are typically solid at room temperature. More energy (heat) is needed to break the structure; think to try to break 1 dry spaghetti strand vs 100 dry spaghetti strands.
In an unsaturated fat molecule, not every carbon atom is bonded with two hydrogen atoms – only some carbon atoms have the double hydrogen bond. The variance in the molecule’s hydrogen bonds is what differentiates a MUFA versus a PUFA. The variance also means the structure is not straight; the structure of unsaturated fat is characterised by a structural kink.
A MUFA has a one double hydrogen bond in its chain – hence mono, meaning one. The remaining carbon atoms are single-bonded. This gives MUFA a boomerang shape. A structural shape like this does not pack together strongly and is why olive oil (70% MUFA) has a low melting point and is liquid at room temperature.
A PUFA has multiple double bonds – hence poly, meaning many. This means there are multiple kinks in the molecule’s chain, giving the molecule a C shape. Similar to the MUFA, this structure does not pack together well.
Chain Length Variance
Chain length refers to the number of carbon atoms in the fatty acid molecule. Most fats are between 16 and 18 carbon atoms in length. However, you do get some fats as low as 4 carbon atoms in length, and other fats longer than 18 carbon atoms in length. Similar to how hydrogen variance affects the properties of a fat, the chain length does so as well. The best way to see this is by comparing SFA that have different chain lengths. Some SFA, like MCT oil, have a majority of short-chain lengths of 8 - 10 carbon atoms and this gives this fat a low melting point – hence why it is liquid at room temperature. Whereas, other SFA, like beef tallow, have a majority of long-chain lengths of 16 - 18 carbon atoms – hence why they are solid at room temperature.
The variance in chain length doesn’t just affect the visual and tangible properties of the fat, but the taste properties of the fat as well. The variance is what gives fats their characteristics of lubricity, viscosity, greasiness, oiliness, and creaminess.
Oxidation is a type of chemical reaction known as Reduction Oxidation (Redox) and is characterised by the transfer of electrons between molecules. The transfer of electrons is a give or take scenario; one is the oxidising agent (the taker), the other is the reducing agent (the giver).
Fats differ in their susceptibility to oxidation; SFA and MUFA are more resilient to oxidation than PUFA – meaning, a PUFA is more likely to give up one of its electrons to an oxidiser.
The next step in understanding oxidation is to introduce three more factors in the oxidation process – auto-oxidation, free radicals, and anti-oxidants.
Fats are heat-, light- and oxygen-sensitive, and exposure to them leads to a free radical-induced reaction called auto-oxidation. Free radicals are molecules that have at least one unpaired electron. They get bitter in their loneliness and so seek to take electrons from other molecules for extra company. Now is where anti-oxidants step in: without anti-oxidants, auto-oxidation becomes a self-propagating process and will lead in time to the complete degradation of the fat. With the presence of anti-oxidants, the process of auto-oxidation is slowed. Free radicals are the takers and anti-oxidants are the givers of electrons.
Antioxidants can be endogenous, produced by our body, or exogenous, present in the food or diet. This is why you see in fats the presence of Vitamin E, which is an anti-oxidant. Vitamin E within the fat is on the lookout for any free radicals so it can give an electron over to the free radical as soon as possible to stop oxidation.
Why all the different fats?
Having now gained a basic understanding of fats, this will help explain why different fats exist. The three types of fatty acids make up most cellular membranes in an organism and determine their properties and functions. Cellular membranes need to maintain optimal fluidity and the presence of the three types of fats will mean the cell membranes can retain optimal fluidity and function in a variety of environments.
Human cell membranes are 50:50 SFA and MUFA. This works for us as we are warm-blooded mammals and maintain consistent body temperature. If our cell membranes were mostly PUFA, the high body temperature would exacerbate auto-oxidation and our cell membranes would be functionally compromised. Similar cell membrane dysfunction would also be seen in salmon, if for example the cell membranes were high in SFA. The cold-water temperature would effectively freeze rigid the cells. The greater the unsaturation of the fatty acid, the more liquid the fat will be at colder temperatures.
The need to consume certain fats, therefore, is heavily dependent on evolved ecology. Humans don’t need much PUFA; hence why humans don’t make their own. On the other hand, humans can make SFA from non-fat sources, such as carbohydrates; this process is known as de novo lipogenesis. From SFA, humans can also make MUFA, through a series of redox reactions. The balance of SFA and MUFA is maintained through an enzyme called Stearoyl-CoA Desaturase-1.
The reason for the different fats is to maintain optimal cell membrane function. Therefore, optimal cell membrane function can be inhibited through the excess consumption and ratios of fats and carbohydrates. And speaking of excess consumption, as it is often the case in western diets, excess calorie consumption is also strongly associated with excess PUFA consumption, in the form of heated PUFA. This combination is a recipe that can lead to some serious negative health outcomes, which is to be discussed next.
Fats and oils are used in nearly all cooking and most cooking will involve heating. As mentioned earlier, some fats are more heat resistant than others, meaning they are less susceptible to oxidation. So when it comes to cooking we want to choose fats that are stable at high heats.
However, for a long time in the science and nutrition world, there has been a big misunderstanding concerning what fats to promote. SFA has been the most vilified of the three fats since the 1960s as it has been purported to be a major cause of heart disease. Whereas, MUFA and PUFA have been marketed as being heart-healthy. It is only really now, where science is starting to prove this wrong, and counter-directionally, catch up with traditional knowledge (think your grandmother and before) and understanding of fats for nutrition and health.
The most popular and most used fats over the last 20 years are all MUFA and PUFA.
The most popular ones being: sunflower, rapeseed, canola, corn, cottonseed, palm, grapeseed, linseed, cottonseed, and rice bran oil. These fats aren’t de facto bad, but it is their utilisation as cooking oils and as the oils of choice for use in ready-made and packaged foods that are hazardous. The food manufacturing process exposes these oils to oxidation, ending in a product that has become denatured and sub-optimal for consumption.
It is the processing that damages the fats; even when these oils are cold-pressed, they still result in highly oxidised oils. The processing destroys the accompanying antioxidants, which would slow auto-oxidation. Even with MUFA, like olive and avocado oil, the manufacturing processes used by most producers leads to the majority of MUFA in the oil being heavily oxidised by the time it reaches the consumer. As this study of the avocado oil industry shockingly shows you are more likely to choose oil that is rancid or not 100% the oil stated on the label.
Here is where the killer fat aspect comes into play. When you consume an already oxidised fat, this fat gets exposed to greater oxidation within the body. As mentioned earlier, free radicals are lonely and are always looking to take an electron from vulnerable molecules. Already oxidised fatty acids are the perfect victim. Free radicals aren’t satisfied with taking only electrons from the fatty acid; it sets off a free radical cascade. This process leads to excessive oxidative stress. Oxidative stress is an imbalance between the natural production of free radicals and antioxidants. When free radicals outnumber antioxidants the denaturing effects expand to damaging, DNA, proteins, and normal metabolic cellular function. This type of damage is implicated in many diseases, ranging from cancer to Alzheimer’s disease and heart failure.
Fats are essential for survival and optimal health: they are an essential energy source for the body, they support immune function, regulate hormones, protect and insulate internal organs, regulate body temperature, maintain healthy skin and hair, and aid in the absorption of the fat-soluble vitamins. It is therefore essential to consume structurally stable fats and in the right ratios.
More structurally unsound fats like MUFA and PUFA are used in most food manufacturing, restaurant cooking and are sold as a healthy alternative to traditional, more stable fats such as butter and tallow. The high consumption of denatured fats is like trying to build a house where the building plans state the need for even shaped bricks to be used throughout, but when it comes to building, all the bricks provided vary in size and shape. This building may be strong in the short term, but over time it is going to be more susceptible to environmental pressure and more likely to form structural weaknesses in certain areas. The steady consumption of denatured fats will over time mean your cells are going to be less robust and more prone to ageing and damage.
Fat ratios refer to the balance of Omega-6 to Omega-3 fatty acids. Historical evidence shows we traditionally consumed Omega-6 and Omega-3 in a 1:1 ratio; however, our modern diets are far from this due to the increasing prevalence of vegetable oil use throughout our food chain. All this adds up and pushes the average Omega-3 to 6 ratios well above 1:1, to a ratio more like 10:1 and above. The ratios matter because omega-6 and 3 compete for the same enzymes, which means the more omega-6 you eat, the less omega-3 will be available. A diet high in omega-6 will increase inflammation, as there will be more oxidation prone omega-6 present in tissues, versus omega-3, which are health-protective.
The science behind fats is important to understand as it helps clarify why fats are essential to our health but clarify how they can damage our health. A healthy body is one where the cells that make up your body are in optimal functioning condition and since those cells are made up of fatty acids, it is essential those cells are being fed the correct fats to ensure cell fluidity and minimise oxidative stress. Due to mistaken conventional advice over the last few decades, advice on fat consumption has been wrong and has led to the proliferation of PUFA and MUFA in our food supply. Coupled with the fact that the processing of these oils at scale can’t be done without damaging the fatty acid molecules and exposing them to oxidation, it means the western diet’s fat intake is dominated by denatured fats with high omega-6 ratios. This sets the stage for increasing levels of inflammation throughout the body and it highlights why it is no surprise that we see such a high prevalence of inflammation-induced diseases.