A method of estimating the energy, protein and fat composition of diets is described, based on 84 food groups. Data from 3 dietary studies are used to compare intake calculated using the food groups and detailed food composition tables, with analyses of duplicate diets. For even small groups of people the mean differences and correlation coefficients between calculated and analysed results are similar for both methods of calculation. This approach could be used as a rapid coding method, or where skilled manpower is not available.