Fat- the dreaded nutrient or so to speak although is it really? Today I am here talking to you about fat, the different types, sources, and requirements. Much like my other two “nutrients explained” on carbohydrates and protein, this is going to give a basic overview.
Fat provides us with approximately 9kcal/ g making it the richest nutrient source of dietary energy. Fat is a long term source of energy for the body, and is stored predominately inthe form of triglyceride’s in adipose tissue. It is estimated that we have enough supply of fat stored to survive for 50 days without eating in comparison to carbohydrates for example where we only have enough supply to last approximately one day. So enjoy, and hopefully you can keep this and refer back if ever you need to refresh your memory!
Functions
Fat is needed for a variety of reasons, which include the following
• Structure- Phospholipids(of which are fats) are a crucial part of our cell membranes which surround each individual cell in the body.
• Protection: A layer of fat inside the body acts as a protector to our organs, this layer also helps to insulate and keep the body warm.
• Omega 3 and omega 6 polyunsaturated fats (essential fatty acids) are especially important for healthy brain function.
• Fat acts as a carrier for the fat soluble vitamins (A,D,E,K) around the body.
• Fats often are used/ added into foods to alter texture and taste.
• Our bodies need to have adequate fat levels in order for normal hormone production to happen and regular enzyme function to occur.
Classification and structure
Fat as we consume it in food is predominately found in the form of a triglyceride. I am going to explain the chemical structure of fats briefly just so you can get a more thorough understanding of the classification, but don’t get too bogged down with the ins and outs of the chemistry , it’s not essential knowledge!
So a triglyceride structurally has a glycerol backbone with three fatty acids attached to it (See diagram 1). Fatty acids are essentially long carbon and hydrogen (hydrocarbon) chains and they vary depending on the number of carbons and hydrogens in the chain (See diagram 2). The characteristics of a fat are determined by the fatty acids attached to the glycerol backbone. Those chains less than 6 carbons long are known as short chained fatty acids, 6-13 medium chained fatty acids and over 14 long chained fatty acids.
Another variation on the fatty acid chains is whether the chain contains a double bond in its structure or not and this leads us onto the topic of saturated and unsaturated fats.
Saturated versus unsaturated fats.
• Saturated fats are those fats whose fatty acid chains contain no double bonds. i.e the fatty acids are only composed of single bonds. • Unsaturated fats- are those fats whose fatty acid chains do contain one or more double bond. • Monounsaturated fatty acids- contain only one double bond in the fatty acid structure• Polyunsaturated fatty acids- contain more than one double or triple bond in the fatty acid structure.
All sources of dietary fat contain both saturated and unsaturated fatty acids in their triglyceride structures. However some fats are classed as saturated and others unsaturated – why is this? Typically the nature of a fat is determined by looking at the proportions of fatty acids present. For example, butter is known as a source of saturated fat because it has more saturated fatty acids in its structure than unsaturated fatty acids. Based on this analogy we can divide fats into 4 main groups1. Saturated2. Monounsaturated3. Polyunsaturated4. Cis/Trans fats
Essential fatty acids- Omega 3/6
Omega 3/6 are polyunsaturated fats and are also known as essential fatty acids. Our bodies can make most of the fatty acids it needs itself however there are two which it cannot those being linolenic acid (omega 6) and alpha linolenic acid (omega 3). Much like the essential amino acids mentioned when I was speaking about protein, we need to get these essential fatty acids from food.
Functions
• Omega 3/6 are extremely important for the brain andpromote positive brain function.
• Omega 3/6 also are needed as precursors to make other fatty acids in the body. For example omega 3 is used to make DHA and EPA two other fatty acids in the body, without a sufficient omega 3 supply EPA and DHA are not able to be synthesised.
The ratio of omega 6 to omega 3 in the body is advised to be 5(N-6):1(N-3) or below. According to research western diets tend to provide a high omega 6:omega 3 ratio (16:1) and this has been found to promote the pathogenesis of some common diseases such as cardiovascular and promote inflammation in the body. (Gómez Candela et al., 2011). Essentially omega 3 intakes are low, and omega 6 high , therefore it is important to ensure you are including many sources of omega 3 in the diet (see sources below) to reduce that ratio.
Cis/Trans fats
These are the fats we want to keep to a minimum in the diet. Cis and trans fats are structurally the same as unsaturated fats so technically they are unsaturated however their propertiesand effects on the body are more similar to saturated fats. Trans fats are found naturally in the ruminants of cow and sheep and therefore in small amounts in beef and milk . They also can be manufactured artificially by adding hydrogen to a liquid vegetable oil causing it to become solid. This artificial process is often done to increase the shelf life of foods and known as hydrogenation.
We are recommended to keep our trans fat intake to below 2% of our overall energy intake a day. In the UK we are thought to be meeting this target with average intakes at about 0.7%. (NDNS,2014).
Sources of Trans fat
Trans fats can be found in foods such as cakes, biscuits, margarine and fried foods. Basically most “treat” foods.
When looking at a label we can identify if a food contains trans-fat by looking for the term “partially hydrogenated vegetable oil”. If you see this term on a label that means the product contains trans fats to some degree.
Fat Metabolism
Metabolism as always is a very complex process in the body and so trying to fully explain the true depth of what happens would take too long and be much to complicated so this is going to be the most simplified explanation!!
Looking at the triglyceride structure above makes this easier to comprehend. Essentially what happens is the triglyceride is broken apart into glycerol and individual fatty acids.
The Fatty acids are then transported attached to albumin bythe bloodstream to tissues. When at the correct tissue the fatty acid binds to a molecule known as co enzyme A and form fatty acyl coA a new molecule. Fatty acyl coA is thentransported into the mitochondria (the energy provider for cells) where ultimately it is used to produce energy for the cells.
How much we need?
In terms of total energy, we are recommended for total fat to make up about 35% of our total daily energy intake. In regard to grams this is about 70g for females and 95grams for males.Further breaking it down• Saturated fat- should account for no more than 11% of daily energy intake. (Equates to approx. 20g for females and 30g for males)• Monounsaturated fat- account for no more than 10% of daily energy intake• Polyunsaturated fat- account for no more than 6.5% of daily energy intake• Cis/Trans fats- account for no more than 2% of daily energy intake
(BNF,2017)
Sources
So the actual important question is where do I get the different types of fat from, what foods?
Saturated fat
• Saturated fat is found predominately in animal based products such as dairy products, milk and cheese. Coconut oil is also high in saturated fat, along with lards and the visible fat on meats/ chicken. Fried foods such as chips, crisps or any sort of deep fried food is a source of saturated fat usually quite high along with pastries biscuits and cakes. Note that palm oil is in fact also a source of saturated fat which is quite unusual considering all the other vegetable oils are unsaturated
Unsaturated fat
• Monounsaturated fats- Conversely unsaturated fats are found mostly in plant based products. Sources of monounsaturated include rapeseed oil, olive oil, avocado, nuts and seeds (pumpkin)
.• Polyunsaturated- similarly also found in plant foods including soya, sunflower, corn and sesame oils. As mentioned above our essential fatty acids omega 3 and omega 6 are polyunsaturated, so sources of 1. Omega 3- oily fish such as sardines and mackerel, vegetable oils including rapeseed, soya and soya products, tofu, nuts such as walnuts, green leafy vegetables and some enriched dairy products. 2. Omega 6- eggs/ egg products, fat spreads, meat and chicken, vegetable oils such as sunflower oil, nuts and seeds once again.
(BNF,2017)
Additional reading and references
GÓMEZ CANDELA, C., BERMEJO LÓPEZ, M., LORIA KOHEN, V., 2011. Importance of a balanced omega 6/omega 3 ratio for the maintenance of health: Nutritional recommendations. Nutrición Hospitalaria. [Online]. 26 (2), pp 323–329, Available from: http://scielo.isciii.es/scielo.php?script=sci_arttext&pid=S0212-16112011000200013&lng=en&tlng=en.
DEPARTMENT OF HEALTH AND SOCIAL CARE. 2014. National Diet and Nutrition Survey Results from Years 1 to 4 (combined).London. Department of Health and Social Care.Available from: https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-results-from-years-1-to-4-combined-of-the-rolling-programme-for-2008-and-2009-to-2011-and-2012
BRITISH NUTRITION FOUNDATION., 2017. Fat[online]. British Nutrition Foundation, Available from: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/fat.html?start=3
The link below gives some more information about omega 3.
Health Aligned 