The K.I.S.S. diet, or 'Keep It Simple Silly', emphasizes an easy-to-follow eating plan using familiar, everyday foods to achieve weight loss and maintenance. It includes simple guidelines such as starting with a lean protein breakfast, incorporating salads or vegetable soups for lunch, and avoiding processed foods and sugar. The author shares personal experiences and encourages moderation, reminding readers that effective weight loss doesn't need to be complicated or expensive.