A few federal websites contain much scientific nutrition information.
MyPlate "provides practical information to individuals, health professionals, nutrition educators, and the food industry to help consumers build healthier diets with resources and tools for dietary assessment, nutrition education, and other user-friendly nutrition information."
SuperTracker is the "USDA's tool to help plan, analyze, and track their diet and physical activity. Find out what and how much to eat, how to track foods, physical activities, and weight, and how to personalize with goal setting, virtual coaching, and journaling."
Other societies of nutrition professionals exist. A few include: the Society of Nutrition Education & Behavior and the International Society for Behavioral Nutrition and Physical Activity.