In the past I discussed the two macronutrients carbohydrates and protein in detail. Today I want to complete my write up of the three macronutrients and provide an introduction to dietary fat.
WHAT IS DIETARY FAT?
Dietary fat is probably the media’s least popular macronutrient. Everywhere you look people are being advised to consume less fat, buy low fat products or even avoid fat completely. However, despite this negative perception dietary fat is an essential part of your diet. It supplies your body with essential fatty acids (EFAs), provides energy, helps your body absorb certain vitamins, helps your body grow and supports a strong immune system.
Dietary fat contains more than double the calories of the other macronutrients with nine calories per gram compared with carbohydrates and protein which both contain four calories per gram. It is constructed from a combination of carbon and hydrogen atoms which are chemically bonded together. The structure of this chemical bond determines the type of dietary fat it will be.
HOW MANY DIETARY FATS ARE THERE?
There are four main types of dietary fat although each of these can be broken down further. Although certain foods may be referred to as a source of saturated fat or a source of trans fats it is never really that simple. Most fat sources are a combination of two or more fat types. For example, whilst olive oil is often referred to as a source of monounsaturated fat it also contains smaller levels of polyunsaturated and saturated fats.
1) SATURATED FATS (SATURATED FATTY ACIDS) (SAFAs):- Saturated fat are those where all the carbon atoms are bonded to hydrogen atoms i.e. they are saturated with hydrogen. They are found mainly in animal products such as meat, butter, cheese and cream. Saturated fats have the highest melting point of all the natural fats and remain solid at room temperature.
2) MONOUNSATURATED FATS (MONOUNSATURATED FATTY ACIDS) (MUFAs):- Monounsaturated fats are those where there is one double bond between carbon atoms. This means the carbon atoms are bonded to hydrogen atoms at all but one point (the double carbon bond). They are therefore not fully saturated with hydrogen atoms (hence the ‘unsaturated’ part of the name) but only at this one point (hence the ‘mono’ part of the name). Monounsaturated fats are mainly found in avocados, nuts and olive oil. They have a lower melting point than saturated fats but a higher melting point than polyunsaturated fats.
3) POLYUNSATURATED FATS (POLUNSATURATED FATTY ACIDS):- Polyunsaturated fats are those where there are two or more double bonds between carbon atoms. This means that they are not fully saturated with hydrogen atoms (hence the ‘unsaturated’ part of the name) and this happens at two or more points (hence the ‘poly’ part of the name). The two main types of polyunsaturated fats are omega 3 fatty acids and omega 6 fatty acids. Omega 3s are mainly found in oily fish whereas omega 6s are mainly found in vegetable oils. Both omega 3s and omega 6s are essential fatty acids which means they cannot be produced by your body and must be sourced from your diet. Polyunsaturated fats have the lowest melting point of all dietary fats and remain liquid at low temperatures.
4) TRANS FATS (TRANS-ISOMER FATTY ACIDS) (TFAs):- Trans fats are those where an originally unsaturated fat has hydrogen atoms added to it. They can be created naturally when a hydrogen bond on an unsaturated fat gets twisted. However, the vast majority of trans fats are man made in a process called hydrogenation. Man made trans fats are mainly found in processed foods such as biscuits, cakes and crisps. They have a high melting point and remain solid at room temperature.
WHICH TYPES OF DIETARY FAT SHOULD YOU CHOOSE?
Conventional wisdom suggest that you should consume mainly unsaturated fats, limit your intake of saturated fats and completely avoid trans fats. The logic behind this is the effect that each type of fat has on your HDL (high density lipoprotein) and LDL (low density lipoprotein) cholesterol levels. LDL cholesterol can build up in the artery walls which causes them to become blocked and restricts the flow of blood through them. Ultimately, this can lead to high blood pressure, increase your risk of heart disease and damage your vital organs. HDL cholesterol removes excess LDL cholesterol from your bloodstream and blood vessel walls then transports it to the liver where it can be processed and removed from the body.
So based on this conventional wisdom unsaturated fats increase HDL cholesterol levels whilst reducing LDL cholesterol levels and therefore come highly recommended. Saturated fats increase levels of both HDL and LDL cholesterol, hence the reason moderate consumption is advised. Man made trans fats are believed to have no health benefits. They increase LDL cholesterol levels whilst reducing HDL cholesterol levels and should be avoided at all costs.
However, more recent research suggests these popular assumptions surrounding dietary fat might not be correct. This article from The Fitness Black Book suggests that instead of going for specific types of fat you should try and eat natural fats whilst avoiding processed fats. Scott (the author) believes that many polyunsaturated fats such as vegetable oils are in fact highly processed, unnatural and unhealthy. Contrastingly, saturated fats come from natural plant and animal products so are therefore good for your health. Monounsaturated fats and certain polyunsaturated fats (such as fish oils) also come from natural plant and animal products meaning that they too are good for your health. Trans fats are largely man made and so should still be avoided completely. Research supports this view with the following article outlining just how important saturated fat is to your body.
In summary when it comes to the four types of fat you should follow the guidelines below…
– Saturated Fats:- OK to consume but make sure they come from natural sources e.g. go for a joint of beef instead of a beef burger.
– Monounsaturated Fats:- OK to consume but make sure they come from natural sources e.g. go for nuts and olive oil instead of margarine and mayonaise.
– Polyunsaturated Fats:- OK to consume but make sure they come from natural sources e.g. go for oily fish, seeds and green leafy vegetables but avoid vegetable oil.
– Trans Fats:- Avoid at all costs.
HOW DOES YOUR BODY USE DIETARY FAT?
When you ingest any type of dietary fat it is broken down into glycerol and fatty acids in the stomach and intestine. Since fats and oils cannot be mixed with water or water based substances such as digestive fluids, the glycerol and fatty acids next need to be altered in a process called emulsification. This process allows fats to be held in the digestive fluids long enough to be digested. Once digested the fat is then transported to your body’s cells via the bloodstream and lymphatic system. If it is not needed immediately, glycerol can be converted into glucose and either used for energy, stored as glycogen (short term) or stored as body fat (long term).
Unlike carbohydrates and protein which have one major function (carbohydrates provide your body with energy and protein acts as building blocks for your body’s cells), dietary fat has a number of important roles in your body. These include:
– Forming the structure of every cell membrane in your body.
– Helping you absorb certain vitamins.
– Lubricating your joints.
– Providing insulation for your nerves.
– Supporting strong bones.
– Supporting a strong immune system.
DIETARY FAT SUMMARY
Dietary fat is often seen as the macronutrient to avoid. However, it is a vital part of your diet so long as you go for natural fats. By choosing the right fats you can keep your cholesterol levels under control and keep your body functioning properly. I hope this article has given you a basic introduction to dietary fat and its importance. In my next few articles I plan to expand on the pros and cons of consuming dietary fat and also recommend a selection of natural fat choices.
Until then I want to hear your thoughts. Do you agree with my recommended fat choices? Is there anything I have missed? Let me know by leaving a comment.
Sources:
Fat (Wikipedia)
Fat Summary (Weight Loss Tips and Secrets)
Digestion of Dietary Fats (CarbSmart)
Proven Health Benefits of Saturated Fats (Organic Natural Health)
The Fat Panel
The Four Types of Fat – Sorting Out the Confusion of Dietary Fats (The Fitness Black Book)