These tablets are manufactured in such a way that they release their contents in the digestive tract over time rather than all at once. One method is enteric coating, where the nutrient is coated with a substance that won't break down in the stomach but will in the small intestine. Another method coats the nutrients with a substance that will be slowly digested, so that the nutrients are gradually released. Both of these (and other) methods can be useful, but care must be exercised in the manufacturing process to ensure the desired results.