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Table 5.5 Plasma lipids of rats (eight to ten per group) fed fats of different stearic acid content for 6 weeks. Fat (% 18:0) Plasma lipid (mg/dl)

Cholesterol1

E/F1,2

Triglyceride1

Corn oil (1.8)

95 ± 4 abc3

4.2 ± 0.1 b

67 ± 4 c

Butter fat (17.6)

84 ± 4 c

5.6 ± 0.2 bc

81 ± 7 bc

Beef tallow (15.8)

97 ± 4 a

5.1 ± 0.5 a

101 ± 9 a

Palm oil (3.7)

101 ± 4 a

3.2 ± 0.3 c

90 ± 5 ab

Coconut oil (2.8)

89 ± 3 bc

3.5 ± 2 bc

90 ± 3 ab

2 E/F = esterified/free cholesterol.

3 Means in vertical column bearing different letters are significantly (P <0.05) different.

rats fed the saturated fats contained more free cholesterol, triglycerides and apolipoprotein E (apoE) than that from the corn oil-fed rats.

Imaizumi et al. (26) fed hamsters diets containing 8% fat with or without 2% cholesterol. The fats were prepared by co-randomization of soybean oil, high-oleic acid safflower oil, and trilaurin, trimyristin, tripalmitin and tristearin. The fats contained 28.4 ± 0.6% oleic acid and 19.5 ± 0.6% linoleic acid. The specific fats contained 51.5% lauric acid, 48.6% myristic acid, 48.9% palmitic acid and 40.1% stearic acid. On the cholesterol-free diets, the rats fed the stearic acid-rich fat had significantly lower plasma cholesterol levels. When the diet contained 0.2% cholesterol, cholesterol levels were similar in all groups. There were no differences among plasma triglyceride levels regardless of dietary cholesterol content. Hamsters fed the stearic acid-rich, cholesterol-free diet exhibited the lowest apparent fat digestibility. Salter et al. (27) fed hamsters diets containing 0.005% cholesterol and 10, 15 or 20% fat. The fats were triolein or triolein plus equal portions of trimyristin, tripalmitin or tristearin. Diets containing tristearin did not increase the cholesterol content of any major lipoprotein fraction.

Atherogenicity of Stearic Acid-Rich Fats

Kritchevsky and Tepper (28) studied the effects of various saturated fats (6%) on atherogenesis in rabbits fed 2% corn oil. The fats compared were corn oil, palm oil, coconut oil and cocoa butter. Cocoa butter was 17% less atherogenic than either palm or coconut oil (Table 5.6).

Connor et al. (29) fed rabbits diets in which 18.5% cocoa butter, coconut oil or hydrogenated vegetable oil was added to chow and fed for 4 (hydrogenated vegetable oil), 10 (coconut oil) or 12 (cocoa butter) months and found no gross aortic atherosclerosis. Addition of saturated fat to a commercial diet will not lead to atherosclerosis in rabbits even when added for a year (30). This is probably due

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Table 5.6 Influence of cocoa butter on atherosclerosis in rabbits fed 2% cholesterol.

Dietary fat

Survival

Serum cholesterol

Average atherosclerosis2

(6%)1

(mg/dl)

Aortic arch

Thoracic arch

Coconut oil

21/22

1652±158

2.24 ± 0.24

1.45 ± 0.21

Cocoa butter

21/22

1556± 130

1.83 ± 0.23

1.17 ± 0.18

Corn oil

21/22

1583 ± 178

1.36 ± 0.21

1.05 ± 0.18

Source: after Kritchevsky and Tepper (28).

1 Rabbits fed 2% cholesterol and 6% fat for 2 months.

2 Aortas graded visually on a 04 scale.

to the high fiber content of the diet. However, addition of saturated fat to a semi-purified diet containing casein, sucrose and cellulose provides an atherogenic diet (31, 32). When such a diet containing corn oil, palm kernel oil, cocoa butter or coconut oil was fed to rabbits for 9 months, the diet containing cocoa butter was significantly less atherogenic than diets containing palm kernel oil or coconut oil (33) (Table 5.7).

Table 5.7 Influence of cholesterol-free, semi-purified diet containing 14% fat on atherosclerosis in rabbits.

Dietary fat (survival)1 Serum cholesterol Average atherosclerosis2

Coconut oil (5/12) Cocoa butter (5/12) Corn oil (5/12)

Serum cholesterol (mg/dl)

Aortic arch 2.10 ± 0.51 ab

  1. 18 ± 0.21 ac
  2. 21 ± 0.07 ab

Source: after Kritchevsky et al. (33).

1 Diets contained 40% sucrose, 25% casein, 14% fat and 15% cellulose. Fed for 9 months.

2 Aortas graded visually on a 04 scale.

3 Values in vertical column bearing same letter are significantly different (P <0.05).

Thoracic arch 1.10 ± 0.24 ab

  1. 25 ± 0.09 ac
  2. 08 ± 0.06 bc

In an earlier study of specific fatty acid effects on experimental atherosclerosis, rabbits were fed 2% cholesterol and 6% of six different fats. The fats were corn oil, randomized corn oil, or corn oil co-randomized with lauric, myristic, palmitic or stearic acid (34). The four co-randomized fats were designed to provide an excess of one specific fatty acid. As Table 5.8 shows, there were no significant differences in severity of atherosclerosis but the atherogenicity of the stearic acid-rich fat was within 5% of that of corn oil, whereas the other saturated fats were 1020% more atherogenic. The most atherogenic fat was the one rich in palmitic acid.

Conclusion

The data show consistently that fats high in stearic acid are consistently less cholesterolemic and atherogenic than are fats containing the other common long-

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Table 5.8 Influence of fats enriched in one specific fatty acid on atherosclerosis in rabbits.

Dietary fat1 Survival2 Serum cholesterol Average atherosclerosis2,3

Table 5.8 Influence of fats enriched in one specific fatty acid on atherosclerosis in rabbits.

Dietary fat1 Survival2 Serum cholesterol Average atherosclerosis2,3

(mg/dl)2

Aortic arch

Thoracic arch

Corn oil

43/46

2633 ±363

1.65 ± 0.13

1.10 ± 0.11

Randomized corn oil

42/46

2022±310

1.59 ± 0.13

1.08 ± 0.10

19% lauric4

41/46

2003 ± 284

1.98 ± 0.15

1.15 ± 0.13

18.2% myristic4

34/46

1883 ±264

1.82 ± 0.12

1.24 ± 0.11

30% palmitic4

42/46

2080 ± 146

2.07 ± 0.14

1.30 ± 0.12

23.4% stearic4

40/46

1977±204

1.74 ± 0.14

1.08 ± 0.09

Source: after Kritchevsky et al. (34).

1 Diets contained 2% cholesterol, 6% fat, fed for 2 months.

2 Values represent average of five experiments.

3 Aortas graded visually on a 04 scale.

4 Appropriate triglyceride randomized with corn oil.

chain fatty acids, namely lauric, myristic and palmitic. The data also suggest that absorbability of cocoa butter is reduced, probably due to its high stearic acid content.

Acknowledgment

Supported, in part, by a Research Career Award (HL00734) from the National Institutes of Health. References

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