a weight-loss strategy that promises dramatic results and is popular for a short period of time. Fad diets usually emphasize one particular food or type of food, and they violate the recommendations in the Dietary Guidelines for Americans, specifically about eating a variety of healthful foods.
Google definition- A fad diet or diet cult is a diet that promises weight loss or other health advantages, such as longer life, and usually relies on pseudoscience rather than science to make many of its claims. In many cases, the diet is characterized by highly restrictive or unusual food choices.