Dietary fat facilitates the utilization of carotenoids and, based on serum beta-carotene or retinol responses following ingestion of meals containing carotene and fat sources, it has been reported that the amount of fat required in a meal may be minimal (approximately 3-5 g). However, the dietary fat requirement for optimal carotene utilization in humans cannot be fully ascertained without longer-term dose-response studies that measure the changes in vitamin A body stores in response to varying levels of dietary fat. In humans, vitamin A body stores can be determined by use of stable isotope-dilution methods. Animal studies have shown that although the level of dietary fat has no effect on serum vitamin A concentrations of animals fed beta-carotene, higher liver vitamin A concentrations were found in those that ingested higher fat levels. Other factors that might influence the relationship of fat intake and beta-carotene utilization include the type of fat ingested, physicochemical properties of the carotenoid source, amount of carotene ingested, whether fat and beta-carotene sources are provided in the same meal, the presence of helminthic infections, age, and vitamin A status.