An introduction to fat
Why do we need fat?
Most people automatically think of fat as ‘bad’ but our bodies can’t function properly without some fats – or fatty acids, to be more accurate. They are an energy source and play a crucial role in all cell membranes – the coat that surrounds every cell in our bodies.
Fatty acids help carry cholesterol and when levels are high, a small amount of good (polyunsaturated) fat can help to carry it off for disposal, rather like bin men! When the bin men go on strike, rubbish accumulates in the streets and it’s much the same inside the body – too much bad (saturated) fat causes rubbish (cholesterol) to be deposited in your arteries and raises the risk of heart disease and stroke.
Fatty acids are needed for healthy hair and skin, they protect our organs, keep our bodies insulated and our brains are largely made up of them. We need fatty acids to carry certain vitamins from food into our bodies and without some fats in our diet, we couldn’t function!
The different types of fat
Here’s the technical bit! Fatty acids come in three categories – saturated, monounsaturated and polyunsaturated, depending upon their structure (a combination of carbon atoms with hydrogen atoms attached – see the illustration right).
Each of these fats behaves differently in the body. Saturated fat is so called because it is saturated with hydrogen atoms. The more saturated it is, the harder it is and usually solid at room temperature, such as lard and butter. Unsaturated fats such as olive and sunflower oil tend to be liquid at room temperature and elastic, vital for membranes, eyes and the brain, for example.
Another type of unsaturated fatty acid, called trans fat, is largely industry-made through a process called hydrogenation – adding hydrogen to low-quality vegetable oils to turn them into butterlike substitutes with a longer shelf-life.
These hydrogenated fats behave more like saturated fats and have no health benefits
– in fact, they’re extremely unhealthy. They raise ‘bad’ cholesterol levels in the same way as saturated fats but more so. Health authorities worldwide recommend that you
avoid trans fats entirely.
Good fat, bad fat
The brain is 60 per cent fat and to work properly must contain enough ‘bendy’
polyunsaturated fatty acids to stay supple and elastic. If fats in the brain are rigid,
its function is affected. Fish require large amounts of flexible, unsaturated fat to
enable them to see and swim around in cold, dim, watery environments.
They obtain them from plankton, algae and other fish. Polyunsaturated fats are also
found in eggs, dairy foods and are plentiful in plant foods – nuts and seeds and their oils, avocados, olives and soya foods, for example. Green leafy vegetables don’t contain a great deal as they are low in all fat.
Olive oil is a monounsaturated fatty acid and a good substitute (in moderation)
for butter and lard in cooking.
We don’t need saturated fat – at all! Found widely in processed foods, meat, dairy, eggs and poultry, it is unhealthy and increases the risk of heart disease and stroke by raising ‘bad’ cholesterol levels. Despite its promotion as a good source of unsaturated, ‘healthy’ fats, much of the fat found in some oily fish is saturated (see table, below). For example, grilled salmon contains the same amount of saturated fat as a roast chicken drumstick.
|Nutritional content of selected oily fish and vegetarian alternatives|
|100 grams of:||Protein (grams)||Fat (grams)||Saturated fat (grams)||Cholesterol (milligrams)||Fibre (grams)||Energy (kcal)|
|Red lentils, boiled||7.6||0.4||Trace amounts||0||1.9||100|
|Kidney beans, boiled||8.4||0.5||0.1||0||6.7||103|
|Tinned chick peas||10.3||2.5||0.2||0||4.3||119|
|Vegetarian style fish fingers (Redwoods)||13.3||15.2||1.9||0||1.0||279|
Contrary to popular belief, all fish and shellfish also contain cholesterol. Prawns,
for instance, contain four times as much cholesterol as rump steak. Plant foods, like
fruits, vegetables, wholegrains, nuts and seeds, contain no cholesterol.
Even fish that are lower in fat than red meat and chicken are not as low in fat
as most vegetarian foods such as fruit, vegetables, pulses and wholegrains.
However it’s dressed up, fish is not a low-fat food and the high levels of cholesterol and saturated fat in some make them a poor choice for fat-reducers.
Getting to know your essential fats
The idea that some fats are essential for growth came from scientists George
and Mildred Burr in the late 1920s. Since then, two polyunsaturated fats have been
classified as ‘essential fatty acids’ – ‘EFAs’. They can’t be made in the body and
therefore have to be eaten. Their names don’t trip off the tongue – linoleic acid (LA)
and alpha linolenic acid (ALA).
Meet the parents
ALA is a ‘parent’ omega-3 EFA as it can be converted by the body to form
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) – both omega-3s.
With omega-6 fats, LA is another parent, converting into GLA (gamma linolenic acid)
and AA (arachidonic acid). Although EPA, DHA, GLA and AA are all important fatty
acids, they are not essential fatty acids (EFAs) as they can be produced in the body from the parent fats ALA and LA.
What’s so essential about EFAs?
EFAs help to make the cell membranes that coat every single cell in our bodies. They are crucial for the brain and nervous system, as well as our eyes and play a part in controlling blood pressure, blood clotting, the immune system and inflammatory responses.
How much fat?
In 2003, the World Health Organisation (WHO) and the United Nations Food and
Agriculture Organisation (UN FAO) issued a joint recommendation setting out how much of each fat we need – monounsaturated, saturated and polyunsaturated. They
measured it in calories (see table, below).
|WHO recommendations for daily fat intake|
|Type of fat||
Percentage of total energy
|Grams required for women (19-50) consuming 1,940 calories/day (kcal)||
Grams required for men (19-50) consuming 2,550 calories/day (kcal)
|Total fat||15-30||32.3 - 64.7||42.5 - 85.0|
|Saturated fat||Less than 10||Less than 21.6||Less than 28.3|
|Polyunsaturated fats||6 - 10||13.0 - 21.6||13.3 - 28.3|
|Omega-6||5 - 8||10.8 - 17.2||14.2 - 22.7|
|Omega-3||1 - 2||2.2 - 4.3||2.8 - 5.7|
Food Standards Agency recommendations for the maximum number of portions of oily fish we should be eating each week (a portion is about 140g)
|Two portions of oily fish||Four portions of oily fish|
|Girls and women who might have a baby one day||Other women|
|Women who are pregnant or breastfeeding||Men and boys|
Many people eat too much fat and to hit these targets, would have to cut down on
the total amount they eat but particularly their saturated fat. Consumption of omega-6 fats has shot up with the popularity of oils such as sunflower and corn oil (and the processed foods that contain them) and these, too, may need to be reduced. On the other hand, most people need to increase their omega-3 intake.
How much oily fish?
In 2004, the UK Food Standards Agency issued guidelines on oily fish intake (see
table, above). The lower limit for breastfeeding mothers and pregnant women (two portions rather than four) is because most oily fish contain low levels of pollutants that can build up in the body. Curiously, the FSA doesn’t seem to think that young boys need protection from toxic pollutants! The health benefits, they say, are greater than the risks so long as you don’t eat more than the maximum. Hardly reassuring!
Most people can obtain all the essential omega-3 fatty acids they need by including
good plant-based sources of omega-3s in their diet, such as flaxseed (linseed), rapeseed and their oils. Flaxseed oil is a particularly rich source containing around two-and-a-half grams of ALA per teaspoonful.
The table (below) shows how much you should aim to include in the diet each day. These fats are easily damaged by light or heat so keep these foods refrigerated. The oils should not be used in cooking; use them on salads in dressing and dips.
|Where to get your daily omega-3s|
|Omega-3 fatty acids||1 daily portion is:|
|Flaxseed (linseed) oil||1-2 tsp|
|Ground flaxseed (linseed)||2 tbsp|
|Rapeseed oil||2 tbsp|
|Hempseed oil||1 tbsp|
|Walnuts||8 halves (28 grams)|
People with diarrhoea, irritable bowel syndrome, diverticulitis or inflammatory bowel disease (Crohn’s disease or ulcerative colitis) should use caution if taking flaxseed (but not flaxseed oil) due to its possible laxative effects. If you have a medical condition, or are taking other drugs or supplements you should consult a doctor or
nutritional therapist before changing your diet.
For adults, EFA deficiency occurs when intakes are less than 1-2 per cent of total
energy intake. Fortunately, damage is rare as even tiny amounts of EFAs can prevent
it. According to the Department of Health, most Western diets provide 8-15 grams of EFAs a day and healthy people carry a body reserve of 500-1,000 grams.
Where low levels of EFA do occur, it’s mostly in infants fed very poor diets. Typical symptoms include excessive thirst, frequent urination, dry or rough skin, dry
hair, dandruff, brittle nails, headaches, stomach ache, diarrhoea and constipation.
Low levels of omega-3 fats in particular are also associated with behavioural problems such as hyperactivityimpulsivity, anxiety, temper tantrums, sleep problems and learning difficulties in some children. More specifically, low levels of DHA omega-3 have been linked with depression, schizophrenia, Alzheimer’s disease and attention deficit hyperactivity disorder (ADHD).
It follows that omega-3 fatty acids are important for the brain and low levels may
affect behaviour, learning and mood. It is important to ensure omega-3 intake by consuming sufficient ‘parent’ EFAs for conversion. Adding them to the diet will reverse any deficiency (see page 12 for good sources).
Balancing the fat
The ratio of omega-6 to omega-3 fats may be more important than the actual amounts of each fat eaten because omega-6 competes with omega-3, essentially cancelling it out. It follows that cutting down on omega-6 may be just as important as increasing omega-3 to get the balance right.
Over the last few decades, consumption of sunflower, corn oil and vegetable fats in processed and baked foods has increased. As a consequence, omega-6 intake has gone up, as has the ratio of omega-6 to omega-3 fats.
Typical diets can produce whopping ratios of 30:1 (omega-6 to omega-3) in contrast to the WHO’s recommendation of between 10:1 and 5:1. Other sources recommend ratios as low as between 4:1 and 2:1 but it’s not an exact science. Be aware of which foods contain which fats and choose accordingly. For omega-3, a good rule of thumb is little and often.
Reduce the use of sunflower, safflower and corn oils, replacing them with olive oil,
flaxseed, rapeseed and soya bean oils.
The body converts the plant omega-3 ALA into the longer chain omega-3s (EPA and
DHA), otherwise found in fish. However, we are repeatedly told – particularly by fish oil
supplement companies – that conversion rates are low and inefficient. The claim that
we cannot convert enough ALA to EPA and DHA is simply not true, but does serve to protect the fish oil market. The better health statistics for vegetarians and vegans – who don’t eat fish – provides proof that they don’t go short.
Several studies have measured the rate at which we convert ALA to EPA and DHA.
A conservative estimate is that about 5-10 per cent of ALA is converted to EPA and 2-5 per cent to DHA. Some studies show much higher levels of conversion (22 and 9 per cent respectively). Furthermore, a recent study revealed that vegetarians convert more than fish-eaters. It seems that we can convert as much or as little as we need, providing we have enough starting material (ALA).
As the body’s fat deposits usually contain ALA, even a very low conversion rate of just 2.7 per cent would allow an average person to make the same amount of EPA as would be found in 18 large (1,000mg) capsules of the omega-3 richest fish oil. Even a person with no omega-3 fats in their body (perhaps after a long-term shortfall in the diet) who takes two tablespoons of flaxseed oil a day can make more EPA than contained in two large fish oil capsules.
In addition to this, we are capable of ‘retroconversion’ – this means we can make EPA from DHA. So if you take an algal supplement that only contains DHA you can boost both DHA and EPA levels without exposing yourself to toxic pollutants found in fish oils. Furthermore, the EPA we make in our bodies has the advantage of being fresher and more stable than that found in fish oils.
If more people knew that they were perfectly capable of producing sufficient amounts of EPA and DHA from ALA they might avoid using rancid, contaminated fish oils and
switch to plant-based omega-3s.
The good stuff
Poor diets can also reduce the rate of conversion, whilst a wide range of nutrients in a good diet (biotin,calcium, magnesium, vitamin B3, vitamin B6, vitamin C and zinc) can improve it. A well-balanced diet rich in fruit, vegetables, pulses, wholegrains, nuts and seeds will provide all these nutrients and more.
The bad stuff
Hydrogenated fat (trans fats) found in some margarines, biscuits and pastries as well as meat, dairy products and alcohol can inhibit conversion.
Too much omega-6 can reduce omega-3 conversion by as much as 40 per cent. Wholefoods such as sunflower seeds, pumpkin seeds, sesame seeds, wheatgerm and soya foods do contain omega-6 but not enough to worry about and they do contain plenty of other healthy nutrients such as fibre, vitamins and minerals.
Using monounsaturated (olive oil) oil instead of polyunsaturated oil ensures that saturated fats, trans fats and omega-6 fats are kept in check. Monounsaturated fats are also found in nuts, peanuts, olives and olive oil, avocados and rapeseed oil.
|A range of nutrients help convert plant omega-3 ALA to the longer chain omega-3s EPA and DHA|
|Biotin||Yeast extract, pulses (peas, beans and lentils), nuts and most vegetables|
|Calcium||Nuts, seeds (especially sesame seeds), tahini (sesame seed paste), pulses, calciumset tofu, calcium-fortified soya milk and green leafy vegetables (not spinach)|
|Magnesium||Green leafy vegetables, pulses, wholegrains, nuts, seeds and avocados|
|Vitamin B3||Yeast extract, peanuts, wholemeal bread, mushrooms, sesame seeds, pulses, (niacin) green leafy vegetables, asparagus, sweet potatoes and carrots|
|Vitamin B6||Bran, wholemeal flour, yeast extract, hazelnuts, bananas, peanuts, currants, garlic (pyridoxine) and most vegetables|
|Vitamin C||Widely available in fruit and vegetables especially oranges, grapefruits, strawberries, blueberries, broccoli, green peppers, spinach and cabbage|
|Zinc||Sesame and pumpkin seeds, green vegetables, lentils and wholegrain foods|
It doesn’t matter how efficiently you convert ALA if you don’t eat enough of it! Working on the WHO’s recommendation of 1-2 per cent in the diet, a woman consuming an average of 1,940 calories per day needs between 2.2 to 4.3 grams of omega-3 fats per day and for men with a 2,550 calorie intake, it is 2.8 to 5.7 grams per day (see table, page 8).
Good sources include ground flaxseeds, hempseeds, rapeseeds and their oils, walnuts, soya beans and products made from them (such as tofu), green leafy vegetables and some species of algae, which may also contain EPA and DHA. You can also buy blended plant oils in health stores that supply omega-3, -6 and -9 fatty acids in the ideal balance (eg Udo’s Choice Ultimate Oil Blend, or Well-Oiled – available from the V VF shop). The table on page 9 should meet most people’s ALA needs
|Plant sources of EFAs|
|100 grams of:||Omega-3 ALA (grams)||Omega-6 grams LA (grams)|
|Flaxseed (linseed) oil||53.30||12.70|
|Rapeseed (canola) oil||09.13||18.64|
|Nuts and seeds|
|Flaxseeds (linseeds) ground, 2 tbsp||22.81||5.90|
|Vegetables, Fruits &Pulses|
|Soya beans, cooked||0.60||4.47|
|Peas (frozen and cooked)||0.02||0.08|
Omega-3s from algae
Fish obtain their omega-3s from eating plankton, algae and other fish that have eaten plankton and algae; wild foods naturally rich in omega-3s. While some algae produce only DHA, recently discovered species contain both EPA and DHA. So, if you’re concerned about conversion, fear not, you can obtain both of these omega-3 fatty acids from algae! Brands are available online.
Algae for omega-3 supplements is usually grown in controlled conditions away from
the sea so it doesn’t impact on marine ecosystems or deprive fish of their natural
food. When fish stocks are declining so rapidly it is highly irresponsible to continue
pushing them as the best source of omega-3s. Alternatives must be found and algae
and other plant sources are the obvious choice. The bonus is that toxin levels are