Western diets saturated fatty acids

A typical Western diet contains approximately 100-300 mg and 20-50 mg of plant sterol and plant stanol, respectively. The relationship between total dietary phytosterol content and the fatty acid composition of the diet decreases with increasing saturated fatty acids, whereas the total dietary phytosterol content increases with increasing PUFA (89). Fortification of lipid foods, such as margarine, with plant sterols will dramatically increase the daily intake of phytosterols and significantly lower serum cholesterol (90). The dietary consumption of large amounts of plant sterols will interfere with cholesterol absorption, thereby leading to an increased daily neutral steroid excretion. 

An abundance of food has obvious consequences it promotes our specific appetites. Lipids account for about 40% of the calories ingested in Western countries, whereas nutritional recommendations are 5-10% lower. This excessive lipid intake, associated with a qualitative imbalance (excess of saturated fatty acids and cholesterol, too high to6/to3 ratio) strongly favours the development of obesity and associated diseases (atherosclerosis, non insulin-dependent diabetes, hypertension, cancer). This attraction to fatty foods is not specific to humans. Rats and mice spontaneously prefer lipid-rich foods if provided with a free choice (Tsuruta et al. 1999 Takeda et al. 2000). This attraction to lipids is so strong that mice given free access to an oil as an optional diet rapidly become obese (Takeda et al. 2001a). The origin of this preference for lipids remains unclear. 

The actual amounts consumed would have no significant nutritional effect. By far the major sources of saturated fatty acids in the US diet (and indeed in most Western diets) are meat and dairy products. Since they are the products of domestic agriculture, it was politically convenient, even if nutritionally irrelevant, to focus a campaign on imported oils. 

Phillips et al. (1999) analysed the plant sterol content of 9 experimental US diets and showed that dietary intakes of plant sterols increased with increasing intakes of polyunsaturated fatty acids and decreasing intakes of saturated fatty acids. In that study, average US diets were found to contain 223-273 mg cholesterol and 138-171 mg total plant sterols, whereas American Heart Association (AHA) National Cholesterol Education Program Step 1 and Step 2 diets contain 264 mg and 274 mg cholesterol, and 189 mg and 208 mg total phytosterols, respectively. Average Western intakes vary from study to study, and are summarized in Table 3. 

Fats and oils always consist of a mixture of fatty acids, although one or two fatty acids are usually predominant. Table 1 shows the fatty acid composition of some edible fats rich in saturated fatty acids. In the Western diet, palmitic acid (Ci6 o) is the major saturated fatty acid. A smaller proportion comes from stearic acid (Ci8 o), followed by myristic acid (Ci4 o), lauric acid (Ci2 o) and short-chain and medium-chain fatty acids (MCFA) (Ci0 0 or less). 

Western diets typically contain low levels of n-3 PUFAs (Simopoulos, Leaf, Salem, 2000). Furthermore, relative to the diet of early man, today s diet is not only higher in saturated fats but has an altered ratio of the two major groups of PUFAs. Modern-day humans are, most probably, descendants of coastal-dwelling hunter-gatherers, with a primary diet of fish, shellfish, and plant matter. This omnivorous, and opportunistic, diet was varied and most probably low in saturated fat. The ratio of n-6 to n-3 fatty acids during the early part of human evolution was close to 1, whereas, today, the ratio is 10 1 or more (Eaton, Eaton, Sinclair, Cordain, Mann, 1998 Simopoulos, 1998). Arecent study in Australia (Sinclair, unpublished) indicates that DHA intake is 0.1 % of fat intake, or about 100 mg/d. The recommended intake is 0.5-1% (Simopoulos et al., 2000). Furthermore, recent data from our group (Sinclair, unpubUshed) has shown that reduced DHA levels in neural tissue occur in animals that are maintained on high saturated fat diets similar to that of a Western diet. 

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