A negative net-calorie food is food that requires more food energy to be digested than the food provides. Its thermic effect or specific dynamic action—the caloric "cost" of digesting the food—would be greater than its food energy content. Despite its recurring popularity in dieting guides, there is no scientific evidence supporting the idea that any food is calorically negative. While some chilled beverages are calorically negative, the effect is minimal and drinking large amounts of water can be dangerous.
Foods that are claimed to be negative in calories are mostly low-calorie fruits and vegetables such as celery, grapefruit, lemon, lime, apple, lettuce, broccoli, and cabbage. These foods are not negative-calorie foods. There is no scientific evidence to show that any of these foods have a negative calorific impact. Celery has a thermic effect of around 8%, much less than the 100% or more required for a food to have "negative calories". A stalk of celery provides 6 calories to the body, but the body expends only half of a single calorie digesting it. Even proteins, which require the most energy to digest, have a thermic energy of only 20%–30%. Diets based on negative-calorie food do not work as advertised but can lead to weight loss because they satisfy hunger by filling the stomach with food that is not calorically dense. A study on chewing gum reports mastication burns roughly 11 calories per hour.
Nutrition experts have pointed out that no foods burn more calories than they provide. However, some foods may be said to have a “negative calorie effect,” which is described as a “calorie-subtracting effect” that occurs as a result of thermogenesis—the transfer of energy to body heat, so that foods cannot deliver to body fat all the calories that they hold. In a 2005 study by Dr. Neal Barnard and colleagues at the George Washington University, published in the American Journal of Medicine, metabolic rates were measured in a group of overweight women. The research participants then began a low-fat plant-based (vegan) diet. The diet allowed unlimited vegetables, fruits, whole grains, and beans, but meat, dairy products, and eggs were excluded and added oils were kept to a minimum. Fourteen weeks later, the participants had their metabolisms measured again. The average after-meal metabolism (the thermic effect of food) had increased by 16 percent, and the average participant had lost 13 pounds. The study attributes the weight loss to the reduced energy density of the foods resulting from their low fat content and high fiber content, and the increased after-meal calorie burn (thermogenesis). 
Water has zero calories and cold water is "negative-calorie" since the body must warm it to body temperature. Some infusions like plain tea and coffee are also effectively zero calorie. The weight loss occasioned from heating chilled beverages, however, is minimal: five or six ice-cold glasses of water burn about 10 extra calories a day and would require about a year to eliminate a pound of fat. (Additionally, excessive water consumption can be dangerous.)
Urban legends that diet soda manufacturers bribe the American FDA to defraud the public have not been proved, but the FDA does permit any food or drink with less than 5 calories per serving to be labelled as containing 0 calories. Replacement of standard sodas with diet ones has been linked to "significant weight loss" by some studies but others have found no benefit at all, as participants simply consumed more calories from other sources. Claims by Coca Cola and Nestlé that their Enviga line of soft drinks had "negative calories" occasioned a false advertising suit against them by the Center for Science in the Public Interest in 2007. The companies settled with the Connecticut Attorney General in 2009, paying hundreds of thousands of dollars and agreeing that any weight-loss-related marketing of the product must be accompanied by disclaimers that weight is only reduced by diet and exercise.
- Upton, Julie (October 2008). "Global Metabolism Myths". Prevention 10 (60): 84, 88. ISSN 0032-8006.. (Google Books link.)
- Webber, Roxanne (3 January 2008). "Does Drinking Ice Water Burn Calories?". Chowhound (CBS Interactive). Retrieved 18 September 2015.
- Nestle, Marion; Nesheim, Malden (18 April 2012). Why Calories Count: From Science to Politics. University of California Press. pp. 189–190. ISBN 978-0-520-26288-1. Retrieved 8 February 2013.
What are these magic foods? Just the low-calorie, high-nutrient-density fruits and vegetables that you might expect to be recommended to someone who is dieting: celery, grapefruit, lemon, lime, apple, lettuce, broccoli, cabbage, and other such items.
- Snyderman, Nancy (6 May 2009). "There Are No Negative-Calorie Foods: Debunking 10 Myths About Dieting". Time.
- Shepphird, Sari Fine (2009). "Question 74". 100 Questions & Answers About Anorexia Nervosa. Jones & Bartlett. p. 171. ISBN 978-0-7637-5450-1.
- Levine, James (30 December 1999). "The Energy Expended in Chewing Gum". The New England Journal of Medicine.
- Barnard ND, Scialli AR, Turner-McGrievy G, Lanou AJ, Glass J. The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity. Am J Med 2005;118:991-997.
- Mikkelson, Barbara (26 August 2013). "Diet Riot". Snopes.
- United States Food and Drug Administration (22 November 2013). "Guidance for Industry: A Food Labeling Guide". Silver Spring, MD: United States Food and Drug Administration. 9. Appendix A: Definitions of Nutrient Content Claims.
- Willett, Walter C.; Koplan, Jeffrey P.; Nugent, Rachel; et al. (2006). "Prevention of Chronic Disease by Means of Diet and Lifestyle Changes". In Jamison, Dean T.; Breman, Joel G.; Measham, Anthony R.; et al. Disease Control Priorities in Developing Countries (2nd ed.). New York: Oxford University Press. p. 834 – via Google Books.
- Godoy, Maria (17 January 2014). "Diet Soda: Fewer Calories in the Glass May Mean More on the Plate". NPR.
- Helm, Burt (31 January 2007). "Coke and Nestle Hit with a Lawsuit for 'Negative Calories'". Business Week.
- Connecticut Attorney General (February 28, 2009). "Attorney General Announces Settlement Resolving Weight Loss, Calorie-burning Claims About Enviga" (Press release). US Fed News Service, Including US State News – via HighBeam Research. (subscription required (. ))