Up until only recently, dietary fat had been given a bad press often being demonised and blamed for the rise in many diseases. This narrative can be traced back many decades to research following World War II, which showed a link between certain types of fat and heart disease. The truth is much more complex. Thankfully, there has been a shift away from this simplistic way of thinking as further research has shown the role of various macronutrients (carbohydrates, proteins and fats) within the body. Nonetheless, the false, anti-fat narrative is still apparent on our supermarket shelves today, where low-fat labelled foods are marketed as the healthy alternative. This may in fact be doing more harm than good as often some of the fats in these foods are replaced with ultra-refined processed substitutes, which have been linked with the rise in chronic diseases such as type 2 diabetes, high blood pressure, heart disease and obesity.
Fats can be broadly categorised into 4 groups: trans fats, saturated fats, polyunsaturated fats and monounsaturated fats. The different types of fats are differentiated on a chemical level by lengths and shape of chains of carbon and hydrogen atoms. These minimal differences can translate into more significant effects on our health. It is important to stress however that a certain food can fall into more than one of the 4 fat groups above. For example, walnuts are rich in polyunsaturated fats, but they also contain monounsaturated fats.
Trans fats are the worst type of fats for our health. They can increase ‘bad’ cholesterol and decrease ‘good cholesterol’. They are linked to an increased risk of heart disease, strokes, fatty liver disease, type 2 diabetes and Alzheimer’s disease. Small amounts can be found in natural sources such as dairy and meat, however the most common source is industrially packaged or processed foods, which tend to be baked or fried. They are often found in margarines, cakes, oils, doughnuts, pastries, ice cream and fast food. These fats are formed by a process known as hydrogenation where hydrogen is added to liquid oil to make it solid and prolong the shelf-life of the food.
Saturated fats were conventionally thought to lie midway between trans fats and unsaturated fats in terms of health risk. Recent research however has shown that the reality is not as straightforward. Saturated fat has been shown to be linked to some risk factors for heart disease but not directly to heart disease itself. It has been shown to increase low-density lipoprotein levels (LDL) levels in the blood – a combination of fat and protein. This is also referred to as ‘bad cholesterol’. However, how much an elevated LDL level actually translates to increased risk of ill health may have been overestimated and can often be dependent on the particle size of the LDL. Small dense LDL particles have an important role in increasing the risk of heart disease whereas larger ‘fluffy; particles which actually tend to be cholesterol-rich are less of a problem. Foods rich in saturated fats include red meats, dairy products, butter, cheese, cream, and coconut oil.
Monounsaturated fats are a healthy type of fat, and are mainly sourced from vegetables, nuts, seeds and oils (particularly olive oil, seed oils and avocado oils). Diets seen in countries such as Greece and Italy have shown a correlation between low rates of heart disease and a high fat diet. The main fat sources in these diets are from extra virgin olive oil, fish oil, nuts and seeds which are all plentiful in monounsaturated fats. This has led to a widespread interest in the Mediterranean-style diet which is considered a healthy choice of eating today.
Polyunsaturated fats are also considered a healthy type of fat. There are 2 main types – the omega 3 fatty acids and omega 6 fatty acids. The numbers refer to the placement of the beginning of the carbon chain and the first double bond (though the chemistry is not something we need to be concerned with). They both confer health benefits. Replacing foods containing trans fats and refined carbohydrates with foods containing polyunsaturated fats are likely to improve cholesterol profile and subsequently reduce risk of heart disease, stroke, fatty liver, kidney disease and Alzheimer’s disease. Omega 3 fats are typically found in oily fish such as salmon, herring and mackerel, sardines, as well as a few plant sources which include flax seed and chia seeds. Omega 6 fats are typically found in walnuts, sunflower and safflower oils, tofu, eggs, almonds and cashews. Both omega 3 and 6 fats are referred to as essential fats. This refers to the fact that the body cannot make them on their own or work efficiently without them and the body needs to obtain them from food.
Omega 6 and Omega 3 ratios
Whilst the importance of polyunsaturated fats to our wellbeing is profoundly important it is noteworthy that our current Western diet has led to an underconsumption of Omega 3 fats. This is important as the ratio of omega 6 to omega 3 that we consume is critical. The standard Western diet has shown ratios of Omega 6 to Omega 3 to be anywhere between 40:1 and 15:1. This has arisen as a result of refined vegetable oils, which have often been described as ‘heart healthy’, being used in the cooking of foods which are often processed. This can push the body into a pro-inflammatory state which can give rise to many medical problems associated with chronic inflammation. These conditions include heart disease, stroke, inflammatory joint conditions, inflammatory bowel disease and Alzheimer’s disease. We should be aiming for a ratio of around 4:1 instead. Accurately measuring our ratios on a practical level is extremely difficult but suffice it to say by increasing levels of omega 3 fats as well as decreasing intake of omega 6 fats we can tip the ratio in our favour.
Omega 3s: Plant and Marine Sources
Just to confuse matters more there are three main types of Omega 3 fats to consider. ALA (alpha linoleic acid), EPA (eicosapentanoic acid) and DHA (docosahexaenoic acid). ALA is mainly found in plant sources whereas EPA and DHA are known as marine fatty acids as they are obtained from fish sources or algae.
Sources of ALA include flax, chia, hemp and soybeans as well as smaller amounts in spinach and kale. ALA needs to be converted to EPA or DHA before we can use it for something other than as an energy source (which is simply the way in which other fats are utilised in the body). Unfortunately, the process by which ALA is converted into these other fatty acids is quite inefficient in humans. Despite this, ALA-containing foods tend to have wider health benefits and should be encouraged as part of a healthy diet.
EPA and DHA have been shown in studies to have a varied number of uses and are important in regulating various biological processes in the body. Both EPA and DHA dampen down the effect of chronic inflammation which may be useful in prevention and treatment of heart disease, stroke, and promoting brain function (hence a link with slowing the decline of Alzheimer’s disease). There has also been an association with improving ADHD (attention deficit hyperactivity disorder), aiding certain eye conditions, lowering high blood pressure and reducing fatty liver disease. EPA specifically has been shown with good quality evidence to improve mood in major depression especially when used with standard antidepressant therapies. High level of intake of DHA has been linked to reduction in risk of prostate, breast and colorectal cancers.
How do I get my Omega-3 if I’m vegetarian?
If you are vegetarian, vegan or quite frankly can’t stomach oily fish, the key is to add a supplement to your diet which contains both EPA and DHA. There are now supplements available which are derived from algae rather than fish oil. Unfortunately, the optimum dose of the supplement is not clear as it very much depends on your own medical history and what therapeutic benefits you are trying to derive from the supplement. As a rule of thumb, I would recommend an Omega 3 supplement with a dosing of around 1000-2000mg or as close to this as possible. You will tend to find that the ratio of EPA to DHA is 3:2 or 2:1.
- Fats are important in our diet.
- The recommended percentage of fat as a component of our daily food intake can vary depending on individual and pre-existing medical problems.
- When consuming fat-containing foods, focus on unsaturated fats ideally in the form of whole foods which include vegetables, nuts, seeds, oils and oily fish.
- The health risks of saturated fats seem to have been overestimated but by focusing on one nutrient we risk missing the bigger picture of what matters most – this is your overall diet and lifestyle.
- Omega 3 is often neglected and under consumed and research to date has shown widespread benefits of omega 3 in whole host of medical conditions.
- Do not be afraid to supplement and tip that omega 3: omega 6 balance in your favour.
- Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials, Mozaffarian D, Micha R, Wallace S. PLoS Med. (2010)
- n-6 fatty acid-specific and mixed polyunsaturate dietary interventions have different effects on CHD risk: a meta-analysis of randomised controlled trials, Ramsden CE, et al. Br J Nutr. (2010)
- Extremely limited synthesis of long chain polyunsaturates in adults: implications for their dietary essentiality and use as supplements, Mélanie Plourde , Stephen C Cunnane. Appl Physiol Nutr Metab (2007)