The Mythology: Spicy food up your metabolism and make you burn fat faster. Spicing foods up means you eat less of it.
The Truth: Thermogenesis yes. No proven effect on weight as yet – more research needed.
Research: There are two chief claims with Capsaicin and spicy food in general. The first is that it promotes satiety by its irritant properties. Secondly that it is thermogenic – or causes the body to produce heat and therefore increases BMI, ‘burning fat’.
Satiety: In several studies a satiety response to Capsaicin has not been consistently demonstrated. It is likely that genetic variability and culture play a role here. It is well known that excessive spiciness which drives appetites in cultures accustomed to eating hot food may have an appetite curbing effect in Westerners.
Thermogenesis: Regarding thermogenesis, Yoshioka’s 1998 study proved that Capsaicin causes the body to preferentially oxidize fat over carbohydrate – in other words to burn fat! 1) Other studies have backed this up and the thermogenic effect of Capsaicin is undeniable. Thermogenesis does not automatically translate into fat loss though, get that straight people! The only 2 long term studies that have looked into this have failed to find any measurable weight loss advantages with subjects ingesting Capsaicin. 2) 3) Having said that, these studies may have been too small to detect a realistic effect.
There are two unknowns in the frontiers of Capsaicin weight loss research. It is well known that people who have a vice for spice tolerate Capsaicin better and have a better thermogenic response. Better thermogenesis could mean more weight loss. Infact any means of improving palatability of Capsaicin added to food, improves thermogenesis and any way of improving palatability may maximize the possibility of fat loss.
Enter Capsinoids – like Capsaicin but without the kick. The thermogenic and metabolic properties of capsinoids appear to mimic those of the more pungent sister compound capsaicin. In a study conducted at the University of Maryland in 2009, forty men and forty women were subjected to a double blind placebo controlled trial with Capsinoids. The really interesting thing is that Capsinoids are non pungent and well tolerated by blandish loving Westerners who faint at the thought of ingesting bucketfuls of Jalapenos. Treatment with 6 mg/d capsinoids orally appeared to be safe and was associated with abdominal fat loss. Capsinoid ingestion was associated with an increase in fat oxidation that was nearly significant.
What’s needed to really settle this once and for all is a large, well conducted head to head study comparing Capsaicin ingested in those used to chilli, those not used to chilli against those ingesting Capsinoids and a bland diet. Measurements would have to made on BMI, energy expenditure, satiety and measures of substrate oxidation. Yeah right dream on! You might have to petition your local Chilli cartel to do just this.
1) Yoshioka M, St-Pierre S, Suzuki M & Tremblay A, Br J Nutr 1998 80, 503–510, Effects of red pepper added to high-fat and high-carbohydrate meals on energy metabolism and substrate utilization in Japanese women.
2) Lejeune MP et al, Br J Nutr. 2003 Sep;90(3):651-59, Effect of capsaicin on substrate oxidation and weight maintenance after modest body-weight loss in human subjects.
Ann M. Coulston, Carol Boushey (2008), Nutrition in the prevention and treatment of disease pp. 464
How it works: One hypothesis claimed that the irritancy of Capsaicin drives thermogenesis by stimulating the sympathetic nervous system which enhances carbohydrate and fat oxidation, promotes satiety and reduces postprandial insulin concentrations, hunger and energy intake.
Adverse effects: Ingestion of spicy food or ground jalapeño peppers does not cause mucosal erosions or other abnormalities. Some mucosal microbleeding has been found after eating red and black peppers. The question of whether chili ingestion increases or decreases risk of stomach cancer is unresolved: a study of Mexican patients found self-reported capsaicin intake levels associated with increased stomach cancer rates (however, this is very likely attributed to helicobacter pylori, while a study of Italians suggests eating hot peppers regularly was protective against stomach cancer. Carcinogenic, cocarcinogenic, anticarcinogenic, antitumorigenic, tumor promotion, and anti-tumor promotion effects of capsaicin have been reported in animal studies.