The yo-yo diet is one type in a class of many extreme fad diets. Also referred to as "weight cycling," the yo-yo diet is characterized by a cyclical pattern of repetitious loss and gain of body weight. Some of the ways people choose to do this include skipping meals and consuming very few calories. However, the yo-yo diet is an infamously unsuccessful and even harmful weight loss technique. Dieters often experience initial success, but due to its overwhelming toll on the body, the inability to sustain this weight loss in the long run causes dieters to regain all of it back and then some.

The term "yo-yo diet" was first coined by Kelly D. Brownell, Ph.D, an American scientist, professor, and esteemed expert on obesity and weight control at Yale University. He named the dieting process due to its analogous nature to the up-down action of a toy yo-yo. Because of the starvation dieters subject their bodies to, their weight loss consists of losing both muscle and body fat. When the body senses that it is rapidly losing its energy source, it kicks on its famine response, a defense mechanism that aims to protect fat stores by using up lean tissue and muscle for energy instead. This weakens the stability of muscles. Because the amount of muscle in the body is directly proportional to metabolic rate, a loss of muscle also means the loss of metabolic rate. While this process naturally occurs in the case of actual famine, it is not appropriate for a regular weight-loss diet.

The yo-yo diet operates in such a way that it is harder each time to lose weight. As the yo-yo nears the end of its string, the plastic spool starts spinning slower. Likewise, the yo-yo diet follower may find weight loss success harder and harder to maintain as time goes by, leading to depression and demotivation. As soon as the dieter starts attempting to eat normally again, all the weight regained will be stored in the form of fat. The yo-yo diet essentially tampers with a healthy body's normal fat-to-muscle ratio, which is a primary aspect of good health.

Fad diets in general are too extreme on the human body. Many times, radical food deprivation is misleadingly perceived as a substitute for good diet and exercise habits. However, people's susceptibility to the yo-yo diet process is the result of many dynamic factors, including biological factors (genetics, hormones, and biochemicals), emotional and motivational support, and misguided expectations. The environment also plays a huge role, since everywhere we turn we face pressures from images in mass media of supposedly perfect body shapes.

Experts agree that the yo-yo diet is not a healthy way to lose weight in the long run. Alternatives that help dieters lose their excess poundage without altering the body's fat to muscle ratio do exist. Some of these tips include:

1. Aiming for realistic weight loss goals
2. Decreasing calorie consumption at a slower pace
3. Not skipping breakfast
4. Modifying activity levels to sustain muscle mass while losing weight
5. Taking a good look at what, when, and why you eat