Within- and between-person variation in dietary surveys: number of days needed to classify individuals.

The variation from day to day, between individuals and within individuals, in the consumption of energy and a variety of nutrients is presented for two groups of executive grade civil servants aged 40-49, numbering 83 and 68 and working in London in 1970-1971, and for 98 drivers and 83 conductors aged 30-67 of London's double decker buses in 1958-1967, a total of 332 men. Each man weighed and recorded his food for at least a week. The reliability with which these men could be classified into extreme thirds of the distribution of individual consumption of the various 'nutrients' or foods on the basis of a single day's or of several days' measurement was calculated. The number of days of measurement required to achieve a given reliability of classification into extreme thirds of the distribution was also estimated. The key is the ratio of the 'between-person' to the 'within-person' variance for the particular nutrient. A diagram is presented of how this ratio is related to the number of days of survey required for a given reliability. Nutrients fall into three main groups--those consumed in relatively large amounts each day (eg protein, fat), those found in moderate amounts in many or most foods but in very large quantities in a few foods (eg dietary cholesterol, calcium), and those which may not be consumed at all by some people but are taken in large quantities by others (eg alcohol). The number of days of survey required for 80 per cent reliable classification of individuals varies from 2 or 3 days for some nutrients like sugar or total carbohydrates to 2 or 3 weeks for others like dietary cholesterol or the ratio of polyunsaturated fatty acids to saturated fatty acids. One day's survey classified no nutrients with 80 per cent reliability in our data, whereas one week's survey classified most nutrients with this reliability or better, although for a few the figure is lower. The precision of a week's survey is also shown in absolute quantities such as grams as distinct from thirds of the distribution. The relevance of these observations to the use of the results of 24-hour surveys in population surveys and correlation and regression analysis is discussed.

Is low energy intake a risk factor for ischaemic heart disease?

The relation between total energy intake and the development of ischaemic heart disease was investigated from a review of all available data including the results of 26 years of follow up from a longitudinal study of diet and ischaemic heart disease. A consistent inverse relation was found, whose strength and consistency are similar to those of other established risk factors. It is concluded that there may be a minimum energy intake below which the risk of ischaemic heart disease is increased.

Total cholesterol, high density lipoprotein-cholesterol and triglycerides after a standardized high-fat meal.

Total cholesterol, high density lipoprotein (HDL)-cholesterol and triglycerides were measured fasting and at 20, 40, 60, 120 and 180 min after a high-fat meal in 22 healthy subjects. Both HDL-cholesterol and total cholesterol fell during the first 20 min after the meal whereas the mean triglyceride level increased during the observation period. In 8 of the subjects the maximum triglyceride level was reached before the end of the observation period and their fasting HDL-cholesterol level was significantly higher than in the rest of the subjects. The higher the fasting HDL-cholesterol concentration, the more rapidly the triglyceride levels returned towards initial values. The study supports the concept that the degradation rate of triglyceride-rich particles is dependent on the HDL-cholesterol level. It also suggests the use of non-fasting triglyceride values in addition to HDL-cholesterol as independent predictors in longitudinal studies for CHD.

Diet and heart: a postscript.

During 1956-66, 337 healthy middle-aged men in London and south-east England participated in a seven-day individual weighed dietary survey. By the end of 1976, 45 of them had developed clinical coronary heart disease (CHD) which showed two main relationships with diet. Men with a high energy intake had a lower rate of disease than the rest, and, independently of this, so did men with a high intake of dietary fibre from cereals. Energy intake reflects physical activity, but the advantage of a diet high in cereal fibre cannot be explained; there was no evidence that the disease was associated with consumption of refined carbohydrates. Fewer cases of CHD developed among men with a relatively high ratio of polyunsaturated to saturated fatty acids in their diet, but the difference was not statistically significant.

Dietary recommendations for the community towards the postponement of coronary heart disease.

The public has recently been confronted with many, often conflicting, recommendations about diet and reducing the risk of coronary heart disease (CHD). Dietary recommendations to the community designed to lower the risk of CHD should be specific, clear, and brief. People should be advised to reduce their intake of foods that are high in saturated fats and replace these partially with foods that are relatively high in polyunsaturated fats. This will lower both total fat and dietary cholesterol intakes and will also change the ratio of polyunsaturated to saturated fats.