By the late 1950s serum cholesterol was emerging as a major risk factor for CHD. Changing a (western) diet, with lower saturated fat and more polyunsaturated fat could reduce serum cholesterol. Controlled dietary trials were started. Between 1965 and 1972 six had reached reporting stage, three small trials from Britain and (one each) from USA, Norway and Finland (see Table 23.1). Four were secondary prevention trials, in subjects who had recovered from a myocardial infarct; two were primary prevention trials, in middle aged people. The first three trials had disappointing results but the next three, in Los Angeles, Oslo and Helsinki were larger, lasted longer and had encouraging results. Years 1965–1972.