Serum cholesterol mmol L

Figure 7.9 The relationship between serum cholesterol and coronary heart disease mortality. From data reported by the Multiple Risk Factor Intervention Trial Research Group (1982) Journal of the American Medical Association 248: 1465-1475.

10 12 14 16 18 20 22 saturated fat, % energy

2 4 6 8 10 polyunsaturated fat, % energy

2 4 6 8 10 polyunsaturated fat, % energy

100 200 300 400 500 600 700 800 cholesterol, mg /day

Figure 7.10 The effects of dietary saturated and polyunsaturated fatty acids and cholesterol on serum cholesterol. From data reported by Keys A et al. (1965) Metabolism 14: 747-787.

100 200 300 400 500 600 700 800 cholesterol, mg /day

Figure 7.10 The effects of dietary saturated and polyunsaturated fatty acids and cholesterol on serum cholesterol. From data reported by Keys A et al. (1965) Metabolism 14: 747-787.

  • It decreases by a factor related to 1 X the intake of unsaturated fat.
  • It increases by a factor related to the square root of cholesterol intake (see section 7.5.1 for a discussion of the effects of dietary cholesterol on synthesis of cholesterol in the body).

Diets that are relatively rich in polyunsaturated fatty acids result in decreased synthesis of fatty acids in the liver (section 5.6.1); this means that there is less export of lipids from the liver in VLDL (section 5.6.2.2), which are the precursors of LDL in the circulation. Polyunsaturated fatty acids (or their derivatives) act via nuclear receptors (section 10.4) to reduce the transcription of the genes coding for acetyl CoA carboxylase and other key enzymes of fatty acid synthesis (section 5.6.1).

In addition, the polyunsaturated fatty acids in fish oil (the ra3 series of long-chain polyunsaturated fatty acids; section 4.3.1.1) have a further protective effect, reducing the stickiness of blood platelets, and hence reducing the risk of blood clot formation. Figure 7.11 shows the beneficial effect of consuming a modest amount of oily fish on the incidence of coronary heart disease — even one fish meal a week reduces the risk to

Figure 7.11 The relationship between habitual fish consumption and coronary heart disease. From data reported by Kromhout D et al. (1985) New England Journal of Medicine 312: 1205-1209.

fish consumption, g/day

Figure 7.11 The relationship between habitual fish consumption and coronary heart disease. From data reported by Kromhout D et al. (1985) New England Journal of Medicine 312: 1205-1209.

all cause IHD

fat 0

fish 0

fibre 0 advice given

Figure 7.12 The effect of advice to eat fish (and other dietary changes) on recurrence of myocardial infarction in middle-aged men who have suffered one infarction. From data reported by Burr ML et al. (1989) Lancet ii: 757-761.

fat 0

all cause IHD

fish 0

fibre 0 advice given

Figure 7.12 The effect of advice to eat fish (and other dietary changes) on recurrence of myocardial infarction in middle-aged men who have suffered one infarction. From data reported by Burr ML et al. (1989) Lancet ii: 757-761.

60% of that in people who eat no fish. Figure 7.12 shows the beneficial effect of following advice to eat fish regularly in a group of men who had already suffered one myocardial infarction.

Figure 7.13 shows the average and desirable proportions of energy coming from saturated, monounsaturated and polyunsaturated fatty acids in the dietary fat. As a general rule, animal foods (meat, eggs and milk products) are rich sources of saturated fats, whereas oily fish and vegetables are rich sources of unsaturated fats.

The recommendation is to reduce intake of saturated fats considerably more than average desirable protein 15%

trans-isomers

polyunsaturated

mono-unsaturated 12%

protein 15%

alcohol

carbohydrate 45%

carbohydrate 45%

saturated 17%

trans-isomers 2%

polyunsaturated

mono-unsaturated 12%

protein 15%

trans-isomers 2%

polyunsaturated

mono-unsaturated 12%

carbohydrate 55%

saturated 10%

figure 7.13 Average and desirable percentage of energy intake from different types of fat.

just in proportion to the reduction in total fat intake. Total fat intake should be 30% of energy intake, with no more than 10% from saturated fats (compared with the present average of 17% of energy from saturated fat). Current average intakes of 6% of energy from polyunsaturated and 12% from monounsaturated fats match what is considered to be desirable, on the basis of epidemiological studies. About 2% of energy intake is accounted for by the trans-isomers of unsaturated fatty acids (section 4.3.1.1), and it is considered that this should not increase.

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