The main components of all fats are the fatty acids which might be saturated, monounsaturated or polyunsaturated. Fats containing a high proportion of saturated fatty acids are solid at room temperature. These are commonly known as saturated fats and are usually derived from animal sources e.g. lard, suet and butter. Most plant fats are high in either polyunsaturated or monounsaturated fats except palm and coconut fat which is highly saturated.
Saturated and monounsaturated fats are not necessary in the diet as they can be made in the human body.
Two polyunsaturated fatty acids (PUFAs) that cannot be made in the body are linoleic acid and alpha-linolenic acid. They must be provided by diet and are known as essential fatty acids. Within the body both can be converted to other PUFAs such as arachidonic acid, or eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
In the body PUFAs are important for maintaining the membranes of all cells; for making prostaglandins which regulate many body processes which include inflammation and blood clotting. Another requirement for fat in the diet is to enable the fat-soluble vitamins A, D, E and K to be absorbed from food; and for regulating body cholesterol metabolism.
Polyunsaturated Fatty Acids – Dietary Sources
Food sources of the two main dietary polyunsaturated fatty acids (linoleic acid and alpha-linolenic acid) are listed below.
Linoleic Acid (Omega 6 family)
Oils made from:
- Evening primrose
Alpha-Linolenic Acid (Omega 3 family)
(Please note – fish is not the only source of omega 3 acids. Flaxseed oil contains twice as much as is found in fish oil!).
- Flaxseeds (linseeds)
- Mustard seeds
- Pumpkin seeds
- Soya bean
- Walnut oil
- Green leafy vegetables
Oils made from:
- Linseed (flaxseeds)
- Rapeseed (canola)
- Soya beans
EPA’s and DHA’s
Alpha-linolenic Acid is converted in the body to EPA (eiocosapentaenoic acid) usually found in marine oil and DHA (docosahexaenoic acid) usually found in marine fish oil. Many factors affect the rate of conversion and one factor seems to be a high food intake of linoleic acid which is typical of vegan diets and may suppress the body’s ability to convert alpha-linolenic acid to DHA. Vegans can achieve a better balance of PUFAs in their body tissues by using less sunflower, safflower and corn oils and more oils containing alpha-linoleic acid such as rapeseed (canola) oil, or soya bean and walnut oils. This would encourage their tissues to make more DHA.
Numerous expert committees have recommended a reduced consumption of total fat by the general population. Only vegan diets generally comply with current guidelines that fat should not contribute more than 35% of the total energy intake of adults and older children.
Saturated fats contribute to high levels of cholesterol in the blood, a risk factor for atherosclerosis and heart disease, while polyunsaturated fats (PUFAs) have the opposite effect. Vegan diets, containing no meat and dairy fats, are low in saturated fatty acids and high in beneficial PUFAs. Vegans consume considerably more of the essential PUFA linoleic acid than do omnivores, and approximately similar levels of the other essential PUFA, alpha-linolenic acid.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two non-essential PUFAs, do not occur in vegan diets. The human body can convert alpha-linolenic acid into EPA and DHA but, even so some of the body tissues of vegans contain less DHA and EPA than those of other dietary groups. The consequences of this difference, if any, are not known.
Similarly, breast milks of vegans, vegetarians and omnivores contain differing proportions of various polyunsaturated fatty acids, and these differences are reflected in some body tissues of infants. It is not yet known what, if any, effect these variations may have on the growth and development of infants.