To judge the effect on blood pressure, the ratio of polyunsaturated to saturated fatty acids (P:S) of foods served to students at two boarding high schools was modified alternately at each school for one school year. The average P:S of the diet of males increased from 0.53 to 0.93 during the intervention whereas among females it increased from 0.64 to 0.98. Comparison of repeated systolic and diastolic blood pressure measurements near the end of the school year did not demonstrate a beneficial effect of the dietary fat changes on the blood pressure of these normotensive adolescents. Compared with the blood pressure patterns during control years, the dietary intervention resulted in slightly higher systolic (+0.88 mm Hg; 95% CI -0.66, +2.42) and diastolic (+1.23 mm Hg; 95% CI = +0.04, +2.42) blood pressure readings among males. Among females the intervention resulted in slightly lower systolic (-0.54 mm Hg; 95% CI = -1.95, +0.88) and diastolic (-0.80 mm Hg (95% CI -2.18, +0.58) blood pressure readings.

Food purchasing and preparation practices were modified in two boarding high schools to increase the polyunsaturated-to-saturated fat ratio (P/S) of the diet of students by changing food products rather than attempting to change eating behaviors. During years when fat-modified products were served, the P/S of males increased by 75 percent, versus a decrease of 6 percent during control years. For females, P/S increased by 53 percent during intervention years, versus an increase of 6 percent during control years.

To judge the effect on blood pressure, sodium intake of students at two boarding high schools was reduced by 15-20% through changes in food purchasing and in preparation practices in the schools' kitchens. Students were not asked to change their usual eating habits. Each school served alternately as the control or intervention school for one school year. Blood pressure was monitored among 341 subjects during control years and 309 subjects during intervention years. Analysis of blood pressure differences between early in the school year and near the end of the school year, with adjustment for sex and initial blood pressure, showed the effect of the dietary intervention to be -1.7 mmHg for systolic (95% CI = -0.6, -2.9, p = 0.003) and -1.5 mmHg for diastolic pressure (95% CI = -0.6, -2.5, p = 0.002). Such modest and easily attainable changes in sodium intake, if maintained, could have a significant effect on the future risk of essential hypertension among young people.