The difference between fat-soluble and water-soluble vitamins lies in their solubility and absorption in the body. Fat-soluble vitamins (A, D, E, K) dissolve in fat and are stored in the body's fatty tissues and liver, allowing for long-term storage. In contrast, water-soluble vitamins (B-complex and C) dissolve in water and are not stored in the body; they must be consumed regularly through diet. Excess amounts of water-soluble vitamins are typically excreted through urine, making it essential to maintain a consistent intake. Understanding these differences is key for adequate nutrition and health.