Fibre

have a specific beneficial effect.' Fish consumption does not directly affect serum cholesterol levels significantly.6' However, the long carbon chain fatty acids present in fish have been found to reduce platelet aggregation in response to contact with the physiological stimulants collagen and adenosine diphosphate. They have therefore a mild anticoagulant effect of potential value in protecting against clot formation in coronary arteries.62 Such fatty acids are important constituents of fish oil and this may be a basis for beneficial effects of fish consumption on CHD incidence. Lastly, fish oil has been found to improve endothelium dependent coronary arterial relaxation in patients with established coronary heart disease (page 72), thus facilitating an increase in blood flow to the heart in response to need.63 In conclusion, eighteenth-century changes in eating habits with a decline in religious observance of dietary constraints and a fall into abeyance of legal restrictions on meat consumption may have resulted in an appreciable fall in fish consumption, possibly to below a suggested critical threshold level. Reduced intake of fish with loss of its various beneficial effects could have contributed to the rising eighteenthcentury coronary heart disease incidence, with its concurrent replacement by fatty animal foods constituting an inter-related additional risk factor.