Master Cleanse is a modified juice fast that permits no food, substituting tea and lemonade made with maple syrup and cayenne pepper. Proponents claim that the diet detoxifies the body and removes excess fat. There is no scientific evidence that the diet removes any toxins, or that it achieves anything beyond temporary weight loss.
Though unlikely to be harmful over the short term, Master Cleanse and similar programs can be harmful over the long term. Short term side effects include fatigue, nausea, dizziness, and dehydration, while long term harm includes loss of muscle mass and increased risk of heart attack.
Nutritionist Jane Clark points to a lack of essential nutrients in this program, citing a deficiency of protein, vitamins, and minerals. As a result of these deficiencies, including far fewer calories than the recommended amount for health and optimum functioning, individuals on the diet may experience headaches and a variety of other symptoms in the short term and the diet is potentially harmful over the long term. According to the Harvard Medical School, the laxative component of the diet can lead to dehydration and electrolyte loss as well as impaired bowel function.
The program has been described as an extreme fad or crash diet, and any weight lost during the fast can be expected to be regained once the diet is stopped. Dietician Keri Glassman has said those following the diet are "guaranteed" to gain weight after stopping.
The diet calls specifically for grade B maple syrup, based on the mistaken belief that the darker colored syrup is less refined than lighter colored grade A or that grade B syrup contains more nutrients. All maple syrup produced according to standard methods is made by exactly the same process. Many trees produce grade A syrup earlier in the spring and grade B later. No maple syrup is refined and there is no evidence that grade B maple syrup contains more nutrients. Color and flavor are the only differences between grades of syrup.
Developer Stanley Burroughs was convicted of manslaughter for practicing the healing methods described in his work. 
- "The dubious practice of detox," Harvard Health Publications
- Stanley Burroughs (1976). The Master Cleanser. Burroughs Books. pp. 16–22, 25. ISBN 0-9639262-0-9.
- Glickman, Peter (2011). Lose Weight, Have More Energy & Be Happier in 10 Days. Peter Glickman, Inc. ISBN 0-9755722-5-3.
- Clarke, Jane. "The nutritionist's view". The Times (London UK): pp. 4. Retrieved 2008-01-30.
- "Do "Detox" Diets Work? Are They Safe?". CBS News. April 23, 2008.
- "Health Advantages of Grade B Syrup", Cornell University Maple Program
- "People v. Burroughs". Google Scholar. Supreme Court of California. 1984. p. 894.