4.5 Fats

Fat, in its principal forms, also contains only carbon, hydrogen and oxygen, and like carbohydrates, forms important tissue energy reserves. Fats are laid down in large amounts in the seeds of plants like nuts and beans, and in the fatty tissues of animals. Other fatty substances have a structural or functional role; one functional role is in the formation of prostaglandins, an important part of the immune system. Two vital structural roles of specific fats (i.e. phospholipids) are the formation of plasma membranes of cells and cellular organelles and in forming the ‘insulation’ that is wrapped around our nerve fibres (known as myelin), without which our nerves could not communicate.

Lecithin is one well-known example of a mixture of phospholipids including phosphatidyl choline and phosphatidyl serine. Nutritionally, lecithin is a health-positive nutrient found in the yolk of eggs and other food sources and nutritional supplements, since it can help support optimal cell function including that of the liver, cardiovascular system and the mitochondrial cell membrane.

Saturated & Unsaturated Fats

Despite similar molecular components, fats are totally different from the carbohydrates in that they do not dissolve in water, dissolving only in organic solvents like chloroform, because their content of oxygen is very small, making them repel water (hydrophobic).

Fats are made up from components called triglycerides, which are comprised of two components; (a) glycerol, which may be known already to you as glycerine and (b) fatty acids. Generally one glycerol combines with three fatty acids to make a triglyceride and in any one triglyceride the three fatty acids that combine may be all the same or may be different (Figure 4.1).

The fatty acids themselves can be divided into two groups based on their structure; saturated and unsaturated depending on the chemical structure of the fatty acid tail. In the intestines, when fats are absorbed, at least a proportion of them are broken down to glycerol and the component fatty acids. None of the saturated fatty acids are essential in our diet but certain polyunsaturated fatty acids, namely essential fatty acids, are required as we can only obtain from certain foods.

A useful way of recognising the amount of saturated or unsaturated fats a food product contains is that fats with a high proportion of saturated fatty acids are generally solids at room temperature, while fats with a high proportion of unsaturated fatty acids are generally oils or soft solids at room temperature.

Examples of saturated fatty acids includes:

• Myristic acid
• Palmitic acid
• Stearic acid
• Arachidic acid

Examples of unsaturated fatty acids include:

• Oleic acid
• Linoleic acid
• Alpha linolenic acid (ALA)
• Arachidonic acid (AA)
• Gamma linolenic acid (GLA)
• Eicosapentaenoic acid (EPA)
• Docosahaexanoic acid (DHA)

Oleic acid is an example of a group known as mono-unsaturated, and is the principal fatty acid of olive oil. All the other unsaturated fatty acids listed above are known as polyunsaturated, due to their chemical structure.

Essential Fatty Acids

Within this vitally important group of polyunsaturated fatty acids there are two subgroups, known as Omega 6 and Omega 3 fatty acids.

Omega 6 comprises:

• Linoleic acid (LA)
• Arachidonic acid (AA)
• Gamma linolenic acid (GLA)

Omega 3 comprises:

• Alpha linolenic acid (ALA)
• Eicosapentaenoic acid (EPA)
• Docosahexaenoic acid (DHA)

These two groups comprise the essential fatty acids (EFA), i.e. those fatty acids which we must have present in the diet as we cannot make them in the body for ourselves. The two subgroups of Omega 6 and Omega 3 are both separately essential. This means that we must have enough of each subgroup in our diet and having more of either one of them will never compensate for insufficiency of the other.

The Omega 6 EFAs occur widely in many foods and are generally easily available. It is especially abundant in most vegetable oils, seeds and nuts. The Omega 3 EFAs are not so well distributed in foods and only occurs in high concentration in oily fish, like salmon and mackerel, fish oil and in linseeds or linseed oil. A moderate amount is present in rapeseed oil, walnut oil, hemp oil, pumpkin seed oil and their respective whole seeds and nuts. Hence, a relative nutritional deficiency of Omega 3 EFAs is a common nutritional problem in our society leading to an altered ratio between Omega 6 and Omega 3 EFA’s.

These unsaturated fatty acids of both subgroups are essential because:

• We cannot make them.
• They are needed within the body as a raw material from which to make a group of hormones called prostaglandins.
• They are needed to maintain the integrity of cell membranes.
• They are involved in many essential functions within the body, from maintaining the integrity of the digestive system to regulating the immune system, and regulating the clotting of blood.

Problems that can arise from not taking the right proportions include susceptibility to cardiovascular diseases, hormone imbalances and under functioning or disorders of the immune system – which may manifest as food or environmental allergies or a reduced ability to resist or recover from infections.

Dietary Fats & Health

One major nutritional problem that our society faces is that fats in general have become subject to over-consumption. In the UK some 40% of dietary energy is coming from fats and oils. Obesity is a worsening problem in our society, through eating too much food, but especially too much “junk” food like chips, burgers and fried breakfasts, though science now suggests that it’s the conversion of excessive dietary sugars that is one of the main causes of obesity rather than the over-consumption of fat per se. This is because fats can be formed in the body from carbohydrates (apart from the essential fatty acids, of course) but carbohydrates cannot be formed from fats. Therefore, it is possible to become obese from having too many carbohydrate foods like bread and potatoes, as well as sugary and processed foods, even if no fat is taken along with them. However, we can still say that over-consumption of fats will not be suitable for optimal function of the cells.

Fats, which contain polyunsaturated fatty acids, are very easily damaged by heat. Frying, or other high-temperature cooking and food processing, especially in the presence of air, produces oxidative damage that converts these fatty acids into altered substances, which our bodies can no longer break down. Processes extracting plant oils from their source also damages the polyunsaturated fats converting the naturally occurring “cis” forms of fats into unnatural “trans” forms. The main production of the trans fatty acid is in the process of hydrogenation, which is still used in making some margarines and cooking fats. Nowadays it is worth looking for products made without hydrogenation, as they will contain no hydrogenated trans fats.

The problem with the trans forms is that our bodies do not have the means to break them down and use them. They therefore become waste products or toxins and are a problem to eliminate, and may interfere with the biological functions which the cis forms of these fats normally carry out. More and more studies are showing that trans fatty acids in foods contribute to serious ailments, especially arterial disease. Please read the following article by clicking on the link below:

Hammad S, Pu S, Jones PJ. Current Evidence Supporting the Link Between Dietary Fatty Acids and Cardiovascular Disease. Lipids. 2016 May;51(5):507-17. Abstract of paper | Full paper