In 1990, Congress passed the 'Nutrition Labeling and Education Act' to clear up confusion over food labels. The 'Recommended Dietary Allowances,' or R-D-A's are the most commonly used guidelines for determining how much of each vitamin and mineral people need to prevent deficiencies. R-D-A's are part of a new set of measurements called 'Dietary Reference Intakes,' or D-R-Is. All nutrients on the label are expressed as a percentage of the daily value that one serving contributes to a 2,000-calorie diet. These recommended amounts are adjusted about every 10 years according to the latest medical research. The U-S Department of Agriculture developed the 'food pyramid' in 1992, an update of post-World War II's 'Basic Four Food Groups.' The base of the pyramid includes the food group that people need the most from: bread, cereal, rice, and pasta. On the next level are two categories: vegetables and fruit. The next level up also contains two categories. First is the 'milk, yogurt, and cheese group;' the other is the 'meat, poultry, fish, dried beans, eggs, and nuts' group. At the top of the pyramid, which the U-S-D-A says should be used 'sparingly,' are 'fats, oils, and sweets.'