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An environmental program directed at the food service departments of two boarding high schools has been tested in a concurrently controlled longitudinal investigation in which the intervention was applied to each school in alternate years. It has been demonstrated that changes in food purchasing and preparation practices can markedly decrease sodium and modify the fat composition of foods, and that such practices result in significant changes in the nutrient intake of students. Even without an educational component for students, who maintained their usual dietary practices, the changes by food service workers led to 15-20% less sodium intake, 20% less saturated fat intake, and an increase in the P/S ratio from 0.46 to 0.84 among students. The change in sodium intake over a school year resulted in lower blood pressure among students receiving the intervention. Adjusting for sex and baseline blood pressure, the estimated effect of the intervention on systolic pressure was -1.7 mmHg (95% C.I. -0.6, -2.9; p = 0.003); for diastolic pressure, it was -1.5 mmHg (95% C.I. -0.6, -2.5; p = 0.002). Such modifications by school food service workers are well accepted and produce very palatable foods. The widespread dissemination of such practices could favorably affect cardiovascular risk factors of students everywhere.

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. (Am J Public Health 1990; 80:1374-1376.) IntroductionIn an effort primarily to decrease the risk of premature cardiovascular disease, many health promotion organizations currently advise that all Americans, including young people, modify the amount and type of fat in their diets. '-3 However, the traditional, one-on-one counseling approach to changing eating behaviors is difficult and time-consuming and is an inefficient method for changing the dietary practices of an entire population. An alternate approach is to change the fat content of food products. This would appear to be particularly relevant today, since such a large proportion of foods consumed in the United States are manufactured,

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.

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