The 17 Day Diet is a diet created by Mike Moreno, a family medicine doctor based in San Diego, CA, USA. The book, titled after the same name as the diet, was also written by Moreno.

The diet consist of three cycles, each 17 days long, plus a fourth long-term plan. Cycle one has the individual eating 1200 calories per day. Cycle two allows the metabolism to reset. Cycle 3 offers more food intake, slowing down the rate of weight loss. Cycle 4 helps maintain the targeted weight, with meal plans and eating habit suggestions.

The diet focuses on healthy eating, and adjusting the body's metabolism and digestive system.

The book has landed on the New York Times' bestsellers for advice books.