Women and girls should reduce their fat intake long before becoming pregnant to protect their fetuses from dangerous dioxins, the Institute of Medicine recommended yesterday. The institute, a part of the National Academy of Sciences, urged the government to educate women about the hazards of dioxins, which can cause health problems ranging from behavioral disorders to cancer and are especially dangerous for fetuses and breast-feeding infants. Dioxins, which are produced by industrial incineration and other processes, contaminate air, water, and soil, and then build up in the fatty tissues of animals. To protect against their dangers, the Institute of Medicine recommended that women cut down on their consumption of dairy products and fatty meats; it also urged the government to work with the agricultural sector to lower dioxin levels in food, replace whole milk with low-fat and skim milk in school lunch programs, and create a database to track dioxin exposure and its effects on fetuses and infants.