Fats

Fats are important for the correct and healthy functioning of the body. Fat has many jobs. Fat helps the absorption of fat-soluble vitamins, A, D, E and K, it provides the highest concentration of stored energy in the body of all the macronutrients (50 to 60,000 Kcals) and it helps with regulating hormones. Fat is also the preferred fuel for the body during lower intensity exercises such as walking, sitting and sleeping.

During long duration and low to moderate intensity exercise periods, fat provides the main fuel source. A small amount is also needed during high intensity exercise (where carbohydrate is predominately used) to help access stored carbohydrate (glycogen). Fat is slow to digest, it can take up to 6 hours. The conversion of stored fat to energy (lipolysis) requires a great deal of oxygen, so exercise intensity must decrease for fat to be able to be used for fuel.

Fat is the dominant fuel source on rest days, due to the low intensity of general life (unless you have a very active job). It’s best not to eat fat immediately before or during exercise, as its long digestion time can cause a sluggish feeling and indigestion. It is also thought that fat can affect oxygen availability, by decreasing nitric oxide (which helps dilation of blood vessels).

The importance of fat

Fat is a misunderstood macronutrient. Different sources offer differing opinions on fat, some saying it’s good for you, others that it’s bad. Like most things, the right fats are essential to health and the wrong ones can be detrimental.

Fat is an important part of a healthy diet. There's more and more evidence that many fats are good for us. Fats can reduce the risk of having a heart attack or stroke. Fat combines with protein to make cell membranes, which are found everywhere in the body. The cells found in the nervous system, particularly the brain, have a high concentration of these fats. They also help with nutrient absorption, nerve transmission, maintaining cell membrane integrity as well as sugar and insulin metabolism, therefore contributing to long-term weight loss and weight maintenance. The balance of these fats is important especially for transition of electrical impulses along the nerves.

The type of fats cell membranes are made from, determines how well the cells can do their job. A cell made of predominantly essential fatty acids, allows a continuous transportation of both nutrients and toxins through the cell membrane. When a cell is made up of too much saturated fat, it becomes rigid, which slows the essential transportation of nutrients and is bad for the cell as well as the whole body.

Prostaglandins are hormone like substances that regulate many chemical reactions, in the immune system, even in bone formation. They are formed from essential fatty acids. Prostaglandins play a huge roll in the regulation of inflammation in the body. For this reason, it is recommended that essential fatty acids be given to people suffering from conditions such as hay fever, eczema and arthritis. Prostaglandins help relax the walls of blood vessels, which in turn can lower blood pressure. Prostaglandins are also essential for muscle contraction, making them important for childbirth and food digestion.

Essential fatty acids are thought to reduce the amount of fats circulating in the blood, helping to decrease the risk of cardiovascular disease, particularly when this is linked to diabetes. They play a role in suppressing tumour formation, particularly in breast cancer. Dry skin, menopausal symptoms, PMS, IBS, and ADD are all thought to improve when the sufferer eats more essential fatty acids. However, other fats are thought to increase our risks of heart disease, certain types of cancer, weight gain, depression and retinal damage of the retina.

The picture below shows a triglyceride. The bluish-green column down the left-hand side is the glycerol backbone, the red portion attached to the glycerol is the carboxyl group. The black chains are the fatty acids. The first two are saturated fatty acids and the third one is an omega 3 fatty acid, as there is a green double bond, 3 carbons from the end of the chain.

Whether fats are saturated, mono-saturated or polyunsaturated is determined by the chemical structure of the fat. You can see this caterpillar shape in the picture above. When the chain is tightly packed with hydrogen ions, it is a saturated fat. When it has one double bond in the chain, it is a mono-unsaturated fat and when there are more double bonds, it is a polyunsaturated fat. How far down the chain the double bond appears gives the fat its name; omega 3, 6, 9 etc. Fatty acid molecules have a methyl group at one end and a carboxylic acid group at the other end. The different structures affect the body in different ways.

Triglycerides are the form in which most fat is stored in the body. Body fat is almost entirely made up of triglycerides and fats are mostly transported in the blood in this form. Triglycerides can come from the fat we eat, or fat which is made in the body from carbohydrates. Chemically, the triglyceride molecules consist of fatty acids joined to a glycerol molecule, as the picture above shows. Too many triglycerides are bad for you.

As the most concentrated source of calories, fat provides nine calories per gram compared with four calories per gram for protein and carbohydrate, which makes them a good source of energy.

Saturated fats

Saturated fatty acids have no double bonds between the carbon atoms of the fatty acid chain and are thus fully saturated with hydrogen atoms. There are many different kinds of naturally occurring saturated fatty acids, which differ by the number of carbon atoms, ranging from 3 carbons (propionic acid) to 36 (hexatriacontanoic acid).

Fat that occurs naturally in tissue contains varying proportions of saturated and unsaturated fat. Examples of foods containing saturated fat include beef, veal, lamb, pork, lard, poultry, butter, cream, milk, cheeses and other dairy products, coconut oil, palm oil and palm kernel oil (often called tropical oils), ghee and chocolate.

Saturated fats in excess raise cholesterol and increase the risk of heart disease, small intestine cancer and stroke. Studies show they are twice as potent at raising your bad cholesterol levels as polyunsaturated fats are at lowering them. The average man should aim to have no more than 30g of saturated fat a day, while the average woman should aim to have no more than 20g of saturated fat a day.

Unsaturated fats

Unsaturated fat is a fat molecule containing one or more double bonds between the carbon atoms. Since the carbons are double-bonded to each other, there are fewer bonds connected to hydrogen, so there are fewer hydrogen atoms, hence unsaturated.

Cis and trans are terms that refer to the arrangement of chains of carbon atoms across the double bond. In the cis arrangement, the hydrogen removed is on the same side of the double bond, resulting in a kink. In the trans arrangement, it is on the opposite side of the double bond, and this causes the chain to remain straight. These are known as trans fats.

Monounsaturated fats

Monounsaturated fats, or MUFAs, are fatty acids that have a single double bond in the fatty acid chain and all the remaining carbon atoms in the chain have a single bond. Monounsaturated fats are considered good fats and help reduce LDL cholesterol, increase HDL cholesterol, reduce triglycerides, blood pressure, help control diabetes and aid weight loss. Nuts including peanuts, walnuts, almonds and pistachios, avocado, canola and olive oil are high in MUFAs.

Polyunsaturated fats

Polyunsaturated fats, also known as essential fats, are made up of omega 3 and 6 and are also known as essential fatty acids. They are called essential fats because they cannot be made by the body, so must be obtained from our diet.

Polyunsaturated fats or PUFAs are fatty acids in which more than one double bond exists within the molecule. That is, the molecule has two or more points on its structure with a double bond. Polyunsaturated fatty acids can assume a cis or trans conformation depending on the geometry of the double bond.

Polyunsaturated fats can be broken down into two categories, omega-3 and omega-6. Omega-3 fatty acids have a double bond 3 carbon atoms away from the methyl carbon (end terminal of the carbon chain, a cluster of carbon and hydrogen atoms). Whereas omega-6 fatty acids have a double bond 6 carbons away from the methyl carbon.

Polyunsaturated fats lower LDL cholesterol, reduce triglycerides, inflammation and tumour growth. They also help to improve immune function and help protect against heart disease.

We need a balance of omega-3 and omega-6 in order to maintain healthy cardiac function, mood stability, insulin balance, joint health and skin health. We need to keep the intake of these good fats balanced because they work in opposition to each other. Too much of one type of fat and not enough of the other can cause a variety of problems. For example, too much omega-6 can cause problems such as degenerative and inflammatory diseases.

Omega-3 is found in foods like canola oil, walnuts, flax seeds, hemp seeds, cold water fish, salmon, mackerel, trout, tuna, sardines, and herring. Recent studies have shown that populations that eat more omega-3’s, such as Eskimos whose diets are heavy in fish, have fewer serious health problems such as heart disease and diabetes. There is evidence that omega-3 oils help prevent or treat depression, arthritis, asthma and colitis and help prevent cardiovascular deaths.

Omega-6 is found in foods like safflower oil, sunflower oil, sesame oil, nuts and beans. Surveys show that most people do not have enough omega-3 in their diet but have too much omega-6.

Polyunsaturated fats should be stored in a cool dark place, as light and heat will damage them, causing free radicals, which are damaging to our bodies. Free radicals are linked with cardiovascular disease, some cancers and increased signs of ageing.

Signs that you are not getting enough essential fats are scaly skin, brittle hair, constipation, poor wound healing, increased infections, depression and visual problems.

Trans fats

The hydrogenation process was patented in 1903 in the US by chemist William Normann. In 1911 P&G noticed that the hydrogenated oil looked and behaved like lard, and began to sell it as a lard substitute under the brand name of Crisco. Because of the lower cost, hydrogenated fats became more established in the 1930s. During World War II their use increased when people turned to margarine and vegetable shortenings as alternatives to butter, which was subject to rationing.

In the 1980s there was a lot of concern regarding saturated fats. Margarines containing hydrogenated vegetable oils were thought to be the healthy option, which boosted their popularity, while butter, coconut oils and palm oil were considered unhealthy.

Some trans fatty acids can be found in the meat and milk of ruminant animals (cattle, sheep, goats, buffalo, deer). There is little evidence that these naturally occurring trans fatty acids are harmful in their native state, as opposed to the synthetic trans fatty acids.

To make trans fats, a process called hydrogenation has to take place. The process of hydrogenation adds hydrogen atoms to cis-unsaturated fats, eliminating double bonds and making them into partially or completely saturated fats. This is an industrial process where oil is heated to very high temperatures (typically 260-270ºC) under pressure and in the presence of a metal catalyst such as nickel, Rayner's nickel, platinum, palladium or cobalt. Then hydrogen is introduced. The catalyst is normally present in the form of a fine powder and one health concern is that a small quantity of it must remain in the oil. The hydrogen is absorbed into the fat molecules, changing its molecular structure and its chemical composition as it converts the unsaturated oil to a more saturated form.

Trans fats were invented as scientists began to hydrogenate liquid oils so that they are better able to withstand food production processes and provide a better shelf life. These fats have a higher melting point, which makes them suitable for baking.

Trans fatty acids are found in many commercially packaged foods, commercially fried foods e.g. French fries, packaged snacks e.g. microwavable popcorn and vegetable shortening.

Partial hydrogenation converts a part of cis-isomers into trans-unsaturated fats instead of hydrogenating them completely. Complete hydrogenation converts the fat into a saturated, hard fat. Hard fats can be softened by cutting with cis fats such as vegetable oil. Therefore trans fats may be monounsaturated or polyunsaturated but never saturated.

Unlike other dietary fats, trans fats are not essential, and they do not promote good health. The body does not recognise trans fats. Consumption of trans fat increases the risk of coronary heart disease by raising levels of LDL cholesterol while lowering levels of HDL cholesterol. It’s associated with a higher risk of developing type 2 diabetes, as well as contributing to weight gain. Health authorities worldwide recommend that consumption of trans fat be reduced to trace amounts. Trans fats from partially hydrogenated oils are more harmful than naturally occurring oils.

The FDA in America estimates that labelling changes for trans fats would prompt changes in eating habits that would save at least $1 billion in annual healthcare costs by preventing 6,400 cases of heart disease per year and at least 2,100 deaths. Others say the benefits could be even greater. Trans fatty acids are responsible for about 30,000 premature deaths per year in America.

Many fast food chains are reducing their use of trans fat usage due to a growing number of organisations pushing for this. These are some useful guidelines to follow to reduce your own trans fat consumption:

• Limit your intake of trans fat to less than 1 percent of total calories. For example, if you need 2,000 calories a day, you should consume less than 2 grams of trans fat.

• Choose a diet rich in fruits, vegetables, whole-grain, high-fibre foods, and full-fat dairy most often.

• Keep total fat intake between 25 and 35 percent of calories, with most fats coming from sources of monounsaturated and polyunsaturated fats such as fish, nuts, seeds and vegetable oils.

• Use naturally occurring, unhydrogenated vegetable oils such as canola, safflower or sunflower.

• If you are eating processed foods, look for those made with unhydrogenated oil rather than partially hydrogenated, hydrogenated vegetable oils or saturated fat.

• Avoid foods that are high in trans fat, such as French fries, doughnuts, cookies, crackers, muffins, pies and cakes.

• Limit the saturated fat in your diet. If you don't eat a lot of saturated fat, you won't be consuming a lot of trans fat.

• Limit commercially fried foods and baked goods made with shortening or partially hydrogenated vegetable oils. Not only are these foods very high in fat, but that fat is also likely to be very hydrogenated, meaning a lot of trans fat.

When a specific food doesn’t list the amount of trans fat on the label, you can use this method to roughly calculate it yourself. Add up the amount of fat in a product (saturated, monounsaturated and polyunsaturated), which is provided on the label. Compare the total number of these, with the total fat shown on the label. If the numbers don't match up, the difference is likely trans fat, especially if partially hydrogenated oil is listed as one of the first ingredients.

Which fats should I cook with?

Having fewer hydrogen atoms on the molecule's surface, due to the double bonds, typically reduces the strength of the compound's intermolecular forces, thus causing the melting point of the compound to be significantly lower. This property can be observed by comparing predominantly unsaturated vegetable oils, which remain liquid even at relatively low temperatures, to much more saturated fats, such as butter or lard, which are mainly solid at room temperature. Trans fats are more similar to saturated fat than cis fats in many respects, including the fact that they solidify at a higher temperature than cis fats.

Fatty acid viscosity (thickness) and melting temperatures increase with decreasing number of double bonds. Therefore, monounsaturated fatty acids have a higher melting point than polyunsaturated fatty acids (more double bonds) and a lower melting point than saturated fatty acids (no double bonds). Monounsaturated fatty acids are liquids at room temperature and semi-solid or solid when refrigerated.

Saturated fats like butter and lard are usually solid at room temperature. They're remarkably stable, and when used for cooking at low heat don't create high levels of toxins. Although ideal for cooking, they are not so good for your arteries and cholesterol levels, as previously mentioned.

Monounsaturated oils are best used cold for salad dressings and not used for cooking, as heat can cause them to be unstable.

Polyunsaturated oils tend to change form when used for frying or cooking. They can generate high levels of toxic aldehydes that can contribute to cardiovascular disease. Therefore polyunsaturated oils should not be used for high temperature cooking, although they're ideal cold as salad dressings.

Oils labelled with 'high smoke point' means that you can heat them to a high temperature without worrying that they will change structure and potentially become harmful. Refined safflower oil or rice bran oil are ideal for deep-frying, both having a high smoke point above 250°C. In comparison, peanut oil has a smoke point of 160°C and butter 177°C. Flax seed oil, which is an omega-3 fatty acid is not so good to cook with, having a smoke point of only 107°C due to those delicate polyunsaturated fats in the oil. You can add it to your food after cooking, as well as include it in cold preparation dressings.

Coconut oil is the oil of choice for cooking because it is nearly a completely saturated fat, which means it is much less susceptible to damage when it is heated. Coconut oil is also thought to be beneficial for heart and thyroid health.

Although the media often portrays olive oil as the healthiest oil, this title does not extend to cooking. Olive oil is primarily a monounsaturated fat. This means that it has one double bond in its fatty acid structure. Although a monounsaturated fat is inherently more stable than a polyunsaturated fat, the overabundance of oleic acid in olive oil creates an imbalance on the cellular level, which has been associated with an increased risk of breast cancer and heart disease.

Friends of essential fats

Vitamin E occurs naturally in foods containing essential fatty acids. It is an antioxidant and works to combat the free radicals formed from these susceptible fats. Other antioxidants that are also protective are vitamin C, selenium and carotene. A healthy gallbladder provides the emulsification agents needed for fats to be absorbed by the body. Essential fatty acids need to go through a system of pathways to be used by the body. The pathways are dependent on vitamins B3, B6, C, magnesium and zinc. As stored oils should be kept in glass bottles in a dark place, seeds need to be kept in the fridge and nuts kept in their shells and stored in a cool place until eaten.

Enemies of essential fats

Over consumption of saturated fats will interfere with the breakdown and absorption of the essential fats. Too much sugar also interferes with essential fat pathways. Stress uses up a lot of important nutrients e.g. magnesium, B-vitamins and zinc, that are needed by these essential fats. Over-exposure to light, heat and food processing damages these fats, turning them rancid.

Common tricks used by the food industry to fool customers, are to say a food is 90 percent fat free. If you imagine that an average portion is 350g, that means it still contains 10 percent fat (35g fat), which is 315 calories from the fat alone. Also be aware when a food is low in fat it is normally replaced with sugar, giving a similar calorie reading.

A few key points to remember about fat

• Remember that heating fat or oil speeds up the process of rancidity.

• Try to avoid adding fat to your cooking, instead try grilling, boiling, poaching or steaming rather than frying.

• Use a non-stick pan and as little oil as possible - oil sprays will greatly reduce the oil used, remember that a tablespoon of oil contains around 130 calories.

• Look at the natural fats that you consume e.g. milk, cheese and butter and aim to choose polyunsaturated, rather than lower fat or skimmed milk.

• When looking at consuming fats in your diet, choose healthier options such as fatty fish, salmon, trout, mackerel, avocados, nuts and seeds which are all high in natural fats.

• Use extra virgin olive oil or nut oils for salad dressings.

• Remember that fat often adds flavour to foods. Avoid fatty foods such as cream cakes, processed meats, hot dogs, pizzas and cheap quality meats.

• Low fat diets (below 10 percent of daily calorie consumption) should be avoided, as these will cause hormonal hunger cravings, due to high fluctuation in blood sugar levels, resulting in greater levels of insulin being released into the bloodstream (see our article on blood sugar for more information).

• Look at getting 15-20 percent of your total calorie intake from healthy fat sources, while aiming to avoid saturated and hydrogenated fat sources.

• Women should try not to consume more than 20g of saturated fat a day, while men should try to stick below 30g per day.

This table shows the constituents of some common oils:

This article has
been written by
Terry Fairclough