WASHINGTON — Calories, saturated fat, trans fat and sodium should be the nutrients highlighted on front-of-package nutrition rating systems and symbols, according to a report issued Oct. 13 by the Institute of Medicine. The I.O.M. said limited space on package fronts as well as the presence of the Nutrition Facts Panel on the backs of all products makes it less crucial for rating systems and symbols to focus on other components, such as cholesterol, fiber, added sugars or vitamins. “Calories, saturated fat, trans fat and sodium present the most serious diet-related risks to people’s health, and many Americans consume far too much of these nutrients,” said Ellen Wartella, chair of the I.O.M. committee that has been studying rating systems and symbols. Ms. Wartella also is Sheikh Hamad bin Khalifa Al-Thani Professor of Communication, professor of psychology, and director, Center on Media and Human Development, School of Communication, Northwestern University. “As Americans grapple with increasing rates of serious health problems connected to their diets, it’s important that the nutritional information they receive is clear, consistent, and well-grounded in nutrition science,” Ms. Wartella said. The findings are “phase 1” of a report that next will review research on how consumers understand and use different types of nutritional information. The I.O.M. report will recommend ways to optimize the usefulness of front-of-package nutrition rating systems and symbols, and will include the committee’s assessment of the pros and cons of having a single, standardized front-label food guidance system that is regulated by the Food and Drug Administration.