Saturated Fats

The main saturated fats in the Australian diet are palmitic (C16:0) and stearic acid (C18:0). There are also smaller amounts of lauric acid (C12:0) and myristic (C14:0). Collectively, saturated fats account for about 40% of the fats in the typical Australian diet. The main food sources are milk, cheese, icecream, fat spreads, meats (especially processed meat), fast foods, processed foods, commercial cakes and biscuits. Myristic acid in butter and dairy fats raises LDL cholesterol (bad cholesterol) the most.
Stearic acid appears to be neutral.

Total saturated fat intake and health

Several large scale population studies have established that there is a significant positive correlation between the consumption of saturated fatty acids and the increased incidence of coronary heart disease (CHD) or increased incidence of secondary events after established heart disease (National Heart Foundation of Australia, Position statement, Aust J Nut Diet 1999). This correlation is most likely secondary to the effects of saturated fatty acids on blood fats, although it may also relate to their prothrombotic properties (Renaud et al. Atherosclerosis 1986; 60: 37-48) or to some other as yet less certain effects such as cardiac arrhythmias.

Saturated fats are undesirable because they decrease the activity of the LDL receptor; this means less LDL-cholesterol (bad cholesterol) is cleared from the blood (i.e. LDL-cholesterol levels rise in the blood). They also increase the tendency for blood clots and may increase visceral fat levels or abdominal fatness because they are less readily mobilised from adipose tissue. In contrast, polyunsaturated (especially fish oils) and possibly monounsaturated fat (from olive oil) sources are more readily mobilised from adipose tissue (Connor. Differential mobilization of fatty acids from adipose tissue. J Lipid Research 1996; 37: 290-298).

The replacement of dietary saturated fat with polyunsaturated fat has been reported to decrease platelet aggregation and clotting activity (Renaud et al. Atherosclerosis 1986; 60: 37-48). Some concern has been expressed that stearic acid may promote thrombosis, but several studies found the opposite effect – an antithrombogenic effect (Tholstrup et al. AJCN 1994; 59: 731-7).

Individual saturated fatty acids and health

It has been recognised that the saturated fatty acids lauric, myristic and palmitic acids elevate the level of plasma cholesterol; they increase both good (HDL) and bad (LDL) cholesterol. Of all the saturated fatty acids, myristic acid appears to be the most potent elevator of plasma cholesterol (Hegsted et al., AJCN 1965; 17:281-95; Zock et al., Arterioscl Thromb 1994; 14: 567-75). In contrast, the saturated fatty acid, stearic acid, appears to have little effect on plasma cholesterol levels (Bonanome et al. NEJM 1988; 318: 1244-8).

A report from the Seven Countries Study analysed food intake over 30 years in samples of 40-60 year olds and correlated this intake with death rates and heart disease deaths over this time (Kromhout et al. Prev Med 1995; 24: 308-15). They showed that:
1. There is a close association between intake of some saturated fat foods and heart disease deaths;
2. Lauric acid and the 14 carbon medium chain myristic acid (found mainly in dairy foods), showed the strongest correlation with early heart attack;
3. A third fatty acid, known as stearic acid (from beef, pork, chicken and mutton) appears to be much less associated with heart disease;
4. Trans fatty acids were also associated with heart disease;
5.Cholesterol in the diet was also associated with heart disease. 

This study represents the largest long term population finding in the field and for this reason alone the results must be regarded seriously.

In a review of all studies to date on fats, Yu et al. 1995 (AJCN 1995; 61: 1129-39) developed a set of formulae to predict the effect of diet on blood fat levels and concluded that stearic acid is not associated with blood lipids, monounsaturated fats tend to decrease blood LDL cholesterol if combined with a low saturated fat diet, and there were indications that blood lipids may be more responsive to diet in men than in women.

Overall, saturated fats increase the risk of CHD, even though they can increase the good cholesterol (HDL).

Unlike other saturated fatty acids, stearic acid has not been found to raise LDL cholesterol, but can increase the good (HDL) cholesterol. So does this mean we can eat foods high in stearic acid to help raise our HDL cholesterol levels? Results from the Nurses Health Study (n=80,000) suggest that a distinction between stearic acid and other saturated fats does not appear to be important in dietary advice to reduce CHD risk, in part because of the correlation between stearic acid and other saturated fatty acids in typical diets (Hu et al. AJCN 1999; 70: 1001-8). Also, the effects of stearic acid on susceptibility to hypertension, cancer, obesity, and other illnesses, are unknown and the data on the activity of saturated fatty acids with regard to thrombotic activity are inadequate. Hence, whether it is desirable to substitute stearate for other fatty acids in the diet is still uncertain.
Fats high in Stearic acid/100g: cocoa butter (33g), beef tallow (19g), chicken fat or pig fat/lard (13g), hydrogenated vegetable shortenings (10g).

Theory into Practice

Ideally, any reduction in total fat should come from reducing animal fats that tend to be high in saturated fat. It is advisable for less than 8% of total energy intake to be obtained from saturated fats e.g. <20g on a 2000kcal intake. Australians consume on average about 12% energy intake as saturated fat.

ONE fast food meal may have more than 50% of your daily fat allowance and about 100% of your daily saturated fat allowance!  (see slide above)

Hydrogenated vegetable oils, especially cottonseed oil, are used extensively by the food industry (e.g. to fry chips and chicken). It is also used to make commercial cakes and biscuits and is often labelled as vegetable shortening.

Hydrogenation of cottonseed oil significantly increases the concentration of atherogenic saturated and trans fatty acids. Beef tallow is used by the fast food industry (e.g. to fry chips - this has a similar amount of saturated fats to hydrogenated cottonseed oil but less trans fatty acids). The food industry is looking at using hydrogenated canola oil because it has a lower concentration of saturated fats than cottonseed oil.  Hydrogenated tropical oils also exist and they contain trans fatty acids.

Tropical oils/milk/cream (e.g. coconut cream/milk) have had a lot of bad publicity due to their high content of saturated fat. However, they are now being investigated for protective phytochemicals; e.g. red palm oil is high in the antioxidant tocotrienol. Traditional communities in Asia and the Pacific Islands have been consuming these oils/milks/creams for centuries with little known adverse effects on health. However, traditionally they have been combined with low energy dense but nutrient dense vegetables and fish dishes. The improved flavour by adding coconut/palm products probably facilitated the consumption of fish and vegetables. The food industry today tends to  use these tropical oils to develop energy dense fried fast food, cakes, biscuits etc. This combination of ingredients may make the tropical fats more adverse to health than when combined with plant/fish in the way traditional societies utilised these products.

Tropical oil/cream/milk consumption has been declining in these Asia Pacific countries, yet heart disease has been increasing.  Interestingly, fish and vegetable consumption has also dropped and it has been suggested that this may be because these dishes are no longer prepared with the flavoursome tropical fats in fear of consuming 'saturated' fat.