Up until a couple of years ago fats were commonly deemed the culprit for weight-gain, raised cholesterol levels and many other diet related diseases. Nowadays we know that eating fat doesn’t actually make one fat. Fat is a vital macronutrient responsible for an array of physiological processes.
Just like amino acids are the building blocks of protein, fatty acids are the building blocks of fats. During digestion, our bodies break down fat into fatty acids which are classified according to the amount of carbon atoms in their chains. Short chain fatty acids (SCFA) contain up to 5 carbon atoms, medium chain fatty acids (MCFA) contain 6-12 carbon atoms and long-chain fatty acids (LCFA) contain 13-21 carbon atoms.
Short-chain fatty acids
When fibre is fermented in the colon, SCFA are produced. SCFA can improve our gut health and have anti-inflammatory, anti-microbial activity. Foods that are high in fibre (fruit, vegetables, legumes) enhance the production of SCFA in our gut. Butyrate is an example of a SCFA that is produced in the gut when high fibre foods such as beans or lentils are consumed. It is also found in certain foods such as cheese and butter. Butyrate is the main source of fuel for cells lining the colon (colonocytes). When these cells don’t obtain the necessary fuel, their function is compromised. Colonocytes provide the gut microbiome with a healthy environment in which they’re able to thrive and are thus a key component in gut health. Instead of eating foods that contain butyrate (butter/cheese) it is more important to focus on consuming foods that increase the number of butyrate-producing bacteria. A diet rich in prebiotics will improve levels of SCFA in the gut. Food sources of prebiotics include artichokes, barley, garlic, oats and onions to name a few.
Medium-chain fatty acids
Medium-chain fatty acids (MCFAs) are found in foods such as coconut oil, palm oil, cheese, butter and milk. Upon ingestion, MCFAs go straight to your liver and are either used as an instant source of energy or are turned into ketones. When the liver breaks down large amounts of fat, ketones are produced (hence the term ‘ketogenic’ diet). Ketones are produced when the body is deprived of carbohydrates and are used by the body as fuel as opposed to glucose from carbohydrates. An example of MCFAs is the increasingly popular, MCT oil. MCT oil was initially used in medical nutrition therapy in patients who aren’t able to digest or absorb short or long chain fatty acids. Such incidences include those with Chron’s or celiac disease. In the last few years MCT oil has become increasingly popular in athletes or used as a potential weight-loss tool. Conflicting evidence exists as to whether athletic performance is improved with the use of MCT oil. Some studies show no difference in endurance time between MCT and LCT trials while others report improved high intensity interval training times with the ingestion of MCT oil. Overall, more research needs to be done with regards to the effectiveness of MCT oil on exercise performance. The same concept applies for those using MCT oil as a means to try and lose weight. There is a lack of consistent evidence with regard to whether or not this works and more trials are currently being carried out to determine the validity of such claims.
Long-chain fatty acids
Long-chain fatty acids (LCFAs) can also be characterised as either saturated or unsaturated fats. The most commonly known LCFAs are omega 3 and omega 6. The omega 3 fatty acids – eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have proven to provide an array of health benefits. Omega 6 fatty acids are essential in small amounts however are pro-inflammatory and can cause problems when eaten in higher proportions. Omega 3 fatty acids do not need to be supplemented if one’s diet contains a variety of foods containing omega 3s. Food sources include fatty fish such as salmon, mackerel or tuna, nuts such as flaxseed, chia or walnuts, plant oils such as soybean oil and fortified foods. Omega 3 fatty acids have been found to exert cognitive benefits and reduce the risk of dementia. They also demonstrate cardioprotective effects, improved retinol functioning (eye health) and improved weight-management. Omega 6 fatty acid consumption has increased significantly since the introduction of Westernized diets. As mentioned above, omega 6s are pro-inflammatory and although inflammation is a normal bodily process, excessive inflammation can lead to tissue damage and other diseases. Omega 6s are found in sunflower oil, corn oil, safflower oil, walnuts and sunflower seeds.
Now that we’ve discussed the building blocks of fats, lets take a closer look into the classification of dietary fats. The four main types of fats found on food labels include saturated, trans and unsaturated fats (monounsaturated and polyunsaturated).
Monounsaturated fatty acids (MUFAs)
MUFAs are largely found in the commonly known Mediterranean Diet. Sources of MUFAs include olive oil, avocados, almonds, hazelnuts, pumpkin seeds and sesame seeds. The consumption of dietary MUFAs has proven to improve blood lipid levels (cholesterol, triglycerides etc), mediate blood pressure and improve insulin sensitivity1. Diets high in MUFAs have shown to have anti-inflammatory and cardiovascular benefits.
Polyunsaturated fatty acids (PUFAs)
Examples of PUFAs include omega 3 and omega 6 fatty acids as previously discussed. In summary, they’re important fats to consume on a daily basis for cognitive, cardiovascular and many other health reasons.
Trans fats are a type of unsaturated fat formed through a process known as hydrogenation. This process converts liquid oils into semi-solids. Studies have stated that the intake of trans fats should be kept as minimal as possible. Trans fats have been linked to various conditions such as cardiovascular disease, certain types of cancer and obesity2. They are mainly found in processed foods whereby hydrogenation of vegetable oils has occurred. Processed foods make up about 80% of the trans fats found in diets while the other 20% comes from naturally occurring fats in animal sources. The majority of sources are found in cakes, pastries, fried potato chips, margarine and microwave popcorn.Having a diet made up of zero trans fatty acids has proven to be difficult and, in some cases, detrimental. This is because certain animal products such as meat and dairy contain trans fats but are also rich in essential nutrients such as protein, calcium and iron2. Certain populations may find it difficult to obtain all of these nutrients from other sources.One should however focus on limiting one’s intake of trans fatty acids. A way in which we could decrease our trans fatty acid consumption would be to read nutrition labels, recognise and avoid processed foods containing trans fats.
Sources of naturally occurring saturated fats include coconut oil, full-fat dairy, palm oil, meat and butter. Foods made with saturated fats include cakes, biscuits and pastries. Decreasing our intake of saturated fats has been a common theme when it comes to nutritional recommendations.
Dietary recommendations stipulate that saturated fats should make up less than 10% of our total caloric intake to reduce cardiovascular disease3. Short chain saturated fatty acids are found in dairy while medium and long chain fatty acids are found in meat, dairy and plant oils3. Different foods contain varying amounts of fatty acids. Varied fatty acid amounts as well as the nutritional composition of the food will influence its physiological effects in the body3. Conflicting evidence exists around saturated fatty acids and whether or not they impact our health in a negative way. However, foods that contain high amounts of saturated fats such as dark chocolate or whole-fat dairy have been shown to not be associated with increased cardiovascular disease3.
According to the Journal of the American College of Cardiology, the overall effect of fats is largely dependent on interactions between naturally occurring fats and those introduced by processing i.e., trans fats. The journal also states that recommendations to avoid all saturated fats were released based on studies performed in the 1960s and 1970s.
The healthiness of fats is a complex topic and is definitely not as simple as determining the saturated fatty acid content3. It is rather a result of the various components found in the specific food item3.In summary, certain forms of fats should not be avoided due to previous ideas that consuming fat results in weight-gain. In fact, certain types of fats such as omega 3 fatty acids have been linked to a decrease in weight. Not to mention all the important roles dietary fats play in order to perform physiological processes. Fats are essential for the absorption of vitamins A, D, E and K and play an essential role in proper brain and nerve functioning.
Although nutrition related information is often conflicting, confusing and controversial, a key message consistent through all evidence-based research would be to focus on decreasing one’s consumption of highly processed foods and increase one’s intake of wholesome, unrefined and unprocessed foods.
Written by Nicole Keeling, Registered dietitian, HPCSA, ADSA
1: Gillingham L, Harris-Janz S, Jones JH P. (2011). Dietary monounsaturated fatty acids are protective against metabolic syndrome and cardiovascular disease risk factors. Lipids. 46(3):209-28. Available from: https://pubmed.ncbi.nlm.nih.gov/21308420/ [accessed 5 October 2021]
2: Dhaka V, Gulia N, Ahlawat KS et al. (2011). Trans fats—sources, health risks and alternative approach - A review. J Food Sci Technol. 48(5): 534-541. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3551118/ [accessed 6 October 2021]
3: Astrup A, Magkos F, Bier DM et al. (2020). Saturated fats and health: A reassessment and proposal for food-based recommendations. J Am Coll Cardiol. 76(7):844-857. Available from: https://www.jacc.org/doi/abs/10.1016/j.jacc.2020.05.077 [accessed 15 October 2021]