By Hazel Grassie
The dietary necessity of fat
Dietary fat serves many roles to human health. Fat is an excellent energy source and essential to the formation of healthy cell membranes, nervous tissue and hormones. Furthermore, fat-soluble vitamins, A, D, E and K, are found naturally in fat-containing foods as it aids the absorption of these vital amines! However, dietary fat has received so much negative media coverage with regards to weight gain and negative health implications. In terms of weight gain, there are a couple of points worth noting. Granted, at 9kcal per gram, fat is an extremely calorific food group, which is why we must be particularly conscious of staying within the guideline daily intake limits. However, overconsumption of any food group in excess of a person’s caloric requirement will lead to weight gain. Achieving and maintaining a healthy weight is simply a matter of having an awareness of calorie consumption and aiming for a balanced, nutritious diet. Secondly, not every fat is the same. Indeed, all fats gram for gram contain the same amount of calories, but their health attributes vary vastly. This is what I aim to clarify and advise upon in ‘Understanding Fats Part 1 and 2’.
Most people will have heard that there are two types of fat – saturated and unsaturated. All fatty acids are made up of a carbon chain to which hydrogen molecules are attached. When every carbon on the chain contains a hydrogen molecule, this is known as a saturated fatty acid. This is what gives fat stability and solidity at room temperature.
On the other hand, unsaturated fatty acids contain at least one double bond between two carbon molecules, meaning that it is no longer saturated with hydrogen molecules. Double bonds cause kinks to form in the carbon chain making it unstable thus, liquid at room temperature. Fatty acids with only one double bond are called mono-unsaturated (MUFA), and fatty acids with many bonds are called poly-unsaturated (PUFA). MUFAs have particular benefits and are often referred to as omega 9 fats. There are two types of PUFAs known as omega 3 and omega 6.
Most people will have also heard of the terms Cis and Trans fats. These are unsaturated fats that behave similarly to saturated fats. Most commonly found in nature and containing health benefits are Cis-unsaturated fatty acids, whereby the hydrogen molecules are both located on the same side of the double bond. Conversely, the hydrogens of a Trans unsaturated fat lay on opposite sides of the bond. Trans fats are uncommon in nature and can be detrimental to health. These fats occur under the combination of high temperatures and hydrogenation. Such processes are used in the manufacture of margarine, turning unsaturated oils into semi-solid substances.
Not all fats are equal
Saturated fat is often labeled ‘bad fat’ as in excess it has the ability to raise LDL, or ‘bad, cholesterol as it promotes dyslipidemia (abnormal amount and deregulation of fats in the blood). Foods high in saturated fat are mostly of animal origin, such as meat and dairy. Such foods include red meat, processed meats, cheese, cream, palm oil, butter, lard and ghee. The government advises that 20-35% of daily calorie intake should come from fat. A maximum of 11% of daily calories should come from saturated fats. For the average man this equates to roughly 30g/day and 20g/day for the average woman. Equally, over consumption of Trans fats found in margarine, snack foods and fried fast-food has consistently been associated with increased risk of coronary heart disease. It is advised that adults should limit trans fat consumption to 5g per day. It is not necessary to remove these fats from the diet completely, but avoid them where possible and replace them with ‘good fats’.
Unsaturated fats are labeled as ‘good fats’ because not only do they maintain bodily processes, but they also have additional health benefits. Research has shown that when dietary saturated fat is replaced with MUFAs, there are reductions in bad cholesterol and improvements in blood lipid profiles (the balance of different lipids in the blood). The Mediterranean diet has a high MUFA consumption, comprised largely by nuts (particularly walnut and cashew), olive oil, avocado, sunflower oil, wholegrain cereals and red meats. This population is amongst the world’s healthiest, in evidence of the MUFA health benefits.
Health benefits of PUFAs are proposed to be even greater. As previously mentioned, there are two types of PUFA known as omega 3 and omega 6. There are three types of omega 3 fatty acids, which play vital roles in human biochemistry; Alpha-linolenic acid (ALA), Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The human body is unable to synthesize EPA and DHA and thus, they are essential and must be obtained through diet. EPA and DHA are found most abundantly in oily fish; salmon, mackerel, anchovies, sardines and trout. ALA is found readily from plant oils like walnut, flaxseed and hemp. The ALA chain can be elongated in the body to become EPA and DHA, but eating small amounts of oily fish is the most reliable way to ensure sufficient levels. Evidence has suggested that omega 3 fats can promote cardiac health, improve circulation and may lower blood pressure. Even stronger evidence indicates that omega fats act as an anti-inflammatory, improve cognitive function and prevent mental disorders.
Another important type of PUFAs are the omega 6 fats; Alpha and Beta linoleic acid. These fats are proven to promote healthy skin, hair and regulate metabolism. Furthermore, they maintain reproductive and bone health. Omega-6 fats are found in some nuts and in vegetable oils such as rapeseed, corn and sunflower. A particular balance between dietary omega 3 and 6 fats is necessary to ensure enough essential EPA and DHA are synthesised. This will be explored further in Part 2.
So there you have it! In short, for a healthier diet it’s necessary to limit saturated fat intake, avoid trans fats wherever possible, and replace these with mono and poly-unsaturated fats, as these have added health benefits. I may have just unveiled more complexity to dietary fats than you were previously aware of, but I hope to have enlightened your knowledge around the topic at the same time.