Why we need fat...
Fats are distributed among all our body cells and fulfil a wide range of structural, storage and metabolic functions. They supply fuel for cells, provide a protective layer around essential organs and form a structural component of brain tissue and the myelin sheath surrounding nerves. Fats form phospholipids, the principal component of cell membranes act as a substrate for various biochemical substances in the body, including hormone and prostaglandin synthesis. Acting as transporters for fat-soluble vitamins, i.e. vitamins A, D and E, fats play a role in micronutrient nutrition. Most crucially, dietary fat - of the polyunsaturated variety - supplies the essential fatty acids.
Essential fatty acids: the facts
Dietary fat is composed principally of triglycerides which consist of glycerol and fatty acids. Fatty acids can be either saturated or unsaturated. This terminology is derived from their chemical structure in that saturated fatty acids contain no double bonds in their structure while unsaturated fatty acids contain one or more double bonds. Those with one double bond are known as monounsaturated fatty acids while those with more double bonds are polyunsaturated fatty acids (PUFAs). Double bonds make the fats more fluid and, thus, more helpful to cell membranes.
Polyunsaturated fatty acids are of two types – omega-6 and omega-3. The parent fatty acids in each of these two groups: linoleic acid (omega-6) and alpha linoleic acid (omega-3) are called ‘essential fatty acids’ because humans and other mammals lack the enzymes to make them in the body. This means we need to consume them from the diet, e.g. from nuts, seeds and the oils and spreads made from these ingredients. These essential fatty acids are the building blocks of many metabolic products, such as prostaglandins, leukotriences and thromboxanes which are important for normal immune function and have a role in inflammatory processes, and neural and optical development.
If the diet lackslinoleic acid and alpha-linolenic acid, these metabolic processes cannot take place efficiently.
GETTING THE FACTS RIGHT:
In response to a BMJ study published on February 6th 2013 which re-analysed data from the 1960s and 70s to suggest that diets high in linoleic acid could increase the risk of cardiovascular death, Dr Carrie Ruxton, an advisor to FIS, notes: “It is important to remember the original findings of the study were that consuming linoleic acid successfully reduced low density lipoprotein (LDL) cholesterol – the ‘bad’ cholesterol linked with heart disease. Many trials over the years have confirmed these results and reported associations between lower LDL cholesterol and a reduced risk of cardiovascular disease.
There's a danger of over-interpreting the BMJ analysis as it only looked at one type of omega-6 fatty, safflower, which is not widely consumed in the UK. Indeed, the study has been criticised by the NHS Choices website which said: “We should not be unduly alarmed (as) the research does not alter our understanding of the possible relationship between diet and cardiovascular risk… British consumers should not panic – the safflower oil used as a source of omega-6 in this study is rarely used in this country”.
“As in all aspects of diet, balance is key and the fatty acids are no exception. Current UK recommendations for total fat and fatty acid intake were published by the Department of Health in 1991 and updated in 1994 in the report on Nutritional Aspects of Cardiovascular Disease. In addition, the Scientific Advisory Committee on Nutrition (SACN) made specific recommendations on intakes of long-chain omega-3 PUFAs in 2004. With regard to PUFAs, an intake range of 6-10% of energy is recommended, while levels of n-6 fatty acids in the diet should stay constant at around 6% of total energy.
In the BMJ study, it is important to note that baseline dietary intake data at the start of the study showed an average linoleic acid intake of about 6% of energy, i.e. the current intakes in the UK diet. The BMJ study does not, therefore, show that current UK intakes of PUFAs are a problem”.
Dr Ruxton says: 'Unsaturated fatty acids of the omega-6 and omega-3 series, specifically linoleic acid and alpha linolenic acid are essential fatty acids as they support many essential metabolic reactions throughout the body. Balance is key and the UK recommendations provide for an intake of PUFAs of 6-10% of dietary energy with current average intakes remaining at about 6% of dietary energy.