A one-food diet is an approach to weight loss that involves the dieter significantly restricting his or her food intake to a single item, sometimes one that is not commonly associated with a healthy eating plan. The idea behind eating only one food for a prescribed length of time is that the body's metabolism may adjust to processing that one food more efficiently when other sources of calories are eliminated. Calorie-counting is usually a focus of a one-food diet because the dedicated dieter will often point out that his or her total daily calories actually add up to less than the recommended average number.

Some well-known single food diets can consist of one food known for its high amounts of sugar, fat, or complex carbohydrates. These diets can include bacon, potatoes, snack cakes, or even beer as the one-food choice. Medical experts advise anyone attempting this kind of weight-loss plan to stay well-hydrated by drinking plenty of water over the course of the plan. Including a multi-vitamin supplement is also recommended. While a one-food diet may be effective for short-term weight loss, the general consensus is that this practice may be unhealthy if followed for a longer time period.

Another version of a one-food diet can focus on internal cleansing in addition to reduced caloric intake. This type of eating plan is designed to use one food as a means of clearing impurities from the body, specifically from the liver. A dieter following a cleansing one-food regimen will eat only one fresh fruit or vegetable such as grapefruit or cabbage for a length of time ranging from one day to a few weeks. Proponents of this weight loss approach believe that it has additional health benefits such as improved energy due to the supposed removal of built-up toxins from the environment and from processed foods.

One possible advantage to a one-food diet is that it can help those struggling with weight loss to have a tighter mental focus when it comes to food choices. Many people may find the wide array of possible diet foods and supplements overwhelming as far as which could be the most beneficial. Following a one-food diet can eliminate those distractions and lead to noticeable results in a relatively short time. Once the dieter has successfully followed this short-term restricted plan, the keys to maintaining his or her accomplished weight loss is to re-introduce a variety of healthy, unprocessed foods and to follow a regular exercise plan.