The power of chili peppers

Taking a bite into a chili pepper (capsicum) elicits a variety of exhilarating responses. The sensation of “heat” when consuming spicy chili peppers is triggered due to its capsaicinoid content, specifically capsaicin. Capsaicin binds to TRPV1 receptors in the mouth, stomach, and small intestine, which triggers the sensation of heat and signals a chemical cascade that activates the sympathetic nervous system and ultimately alters energy expenditure and metabolism (Szallasi & Blumberg, 1999).

Fatty Acid Oxidation

A recent meta-analysis of 12 studies by Ludy et al. (2012) reported that both moderate and high doses of capsaicin increase fatty acid oxidation. Most stimulant based weight loss supplements increase fatty acid oxidation by mimicking or stimulating catecholamine (adrenalin) release. Catecholamines bind beta-receptors in adipose tissue and stimulate the release of fatty acids (lipolysis). Unlike stimulants, Bloomer et al. (2010) reported 2 mg of capsaicinoids increase lipolysis without affecting heart rate or blood pressure. This suggests that capsaicin ingestion may improve body composition without placing unneeded strain upon the heart.

Uncoupling proteins (UCPs) are associated with the mitochondria and increase energy expenditure by enhancing thermogenesis and improving fatty acid transport (Ricquier & Bouillaud, 2000). UCP isoforms are located in both adipose tissue and skeletal muscle, and are both activated by the sympathetic nervous system. Masuda et al. (2003) reported enhanced UCP induction in conjunction with reduced epididymal fat pads in mice supplemented with the capsaicin analogue capsiate and fed equal energy diets.  UCP levels were found to increase in both white adipose tissue and skeletal muscle tissue. Additionally, plasma fatty acid concentration and fatty acid oxidation was increased. Because both groups of mice were fed equally, Masuda et al. concluded that this increase in energy expenditure with capsiate ingestion was due to suppressed body fat accumulation and enhanced fatty acid translocation and oxidation in skeletal muscle mitochondrion.

Recently, peroxisome proliferator-activated receptor-alpha (PPARα) has been implicated in the treatment of obesity and the enhancement of body composition. When activated, PPARα enhances energy expenditure by increasing the uptake and oxidation of fatty acids by the liver and skeletal muscle (Kersten et al., 1999). Currently, a number of drugs are being developed to agonize PPARα in order to reduce inflammation and treat obesity (Motillo et al., 2012). Interesting, capsaicin has been shown to bind and activate PPARα in hepatocytes (Kang et al., 2010). Therefore, chili pepper consumption may provide an easy, natural way to increase fat oxidation and nutrient partitioning.

Appetite

Capsaicin reduces both sensations of hunger and the desire to eat fatty foods, sweet foods and salty foods (Ludy & Mattes, 2011). Further, capsaicin consumption improves satiety and reduces hunger during periods of caloric restriction (Reinbach et al., 2009). Capsaicin may improve satiety and reduce food intake by altering the hormonal profile of exigenic hormones. Capsaicin has been shown to suppress ghrelin while increasing glucagon-like peptide 1 secretion (Smeets et al., 2009). Ghrelin is a fast-acting hormone that initiates the drive to eat (Klok et al., 2007) where as glucagon-like peptide 1 promotes satiety and improves glucose clearance via insulin secretion (Rotella et al., 2005). Therefore, it is likely that chili pepper consumption reduces appetite via both peripheral (heat sensation) and central (hormonal) mechanisms.

Energy Expenditure and Body Composition

Thermogenesis describes the biological production of heat, and is generally accomplished via an elevation in metabolic rate. Capsaicin ingestion enhances thermogenesis by increasing energy expenditure, in part by SNS activation. Lejune et al. (2003) reported enhanced fatty acid oxidation in conjunction with a 135 kcal/day increase in energy expenditure following consumption of 135 mg of capsaicin. Using more practical numbers, researchers have reported a 1-2 kcal/kg increase in energy expenditure with 9 mg of capsaicin consumption (Lee et al., 2010). Capsaicin consumption may also enhance the caloric cost of exercise: Josse et al. (2010) reported that 10 mg of capsaicinoids elevated caloric expenditure by .24 kcal/min during cycling.

The effects of capsaicinoid ingestion on body composition have been equivocal. Some studies have shown reductions in body weight and body fat accumulation by 3.8 lbs and 3.0 lbs, respectively, following 2 weeks of high capsaicinoid consumption (Kawabata et al., 2006). Other studies, however, have been less impressive. Despite improvements in energy expenditure and fatty acid oxidation, Inoue et al. (2007) reported a 0.75 lb decrease in body fat over the course of 4 weeks. Differences in study design, such as the controlled feeding environment in Kawabata vs. free living in Inoue may explain the discrepancy in the results.

Inflammation

Low-grade, chronic, systemic inflammation is a biomarker of nearly every chronic disease including diabetes, metabolic syndrome, heart disease, and cancer. Whether inflammation is a cause of symptom is unknown (Esposito & Giugliano, 2004), and likely it is a cyclical process. What we do know is that chronic elevation of inflammatory cytokines such as C-reactive protein (CRP), interleukin-6 (IL6) and tumor necrosis factor-alpha (TNF-α) are associated with insulin resistance (Hotamisligil, 1999), cancer (Coussens & Werb, 2002), and post-prandial protein synthesis inhibition (Balage et al., 2010).

Wide arrays of supplements have been marketed to reduce systemic inflammation. Some, such as curcumin may be effective in lowering inflammation (Kuo et al., 2012), whereas many others such as stinging nettle are ineffective. Consuming whole chili peppers may be an effective way to positively modulate inflammation. Capsaicin consumption has been shown to reduce inflammation and restore insulin sensitivity in diabetic mice, in part by suppressing TNF-α and IL-6 expression (Kang et al., 2010). In addition to reducing pro-inflammatory cytokines, capsaicin also protects the anti-inflammatory cytokine IkB-a against lipopolysaccharide (LPS) induced degradation (Kim et al., 2003).  If you recall from the probiotic blog, LPS is produced by gram-negative (bad) bacteria in the gut, readily absorbed, and stimulates systemic and neuro-inflammation (Lee et al., 2008).

Conclusion and Recommendations

The capsaicinoids in chili peppers provide an array of health and performance benefits. Capsaicin consumption appears to reduce food cravings and improve satiety during both a normal and an energy restricted diet. This makes chili peppers an excellent food choice for individuals who need to adhere to a specific energy intake.

Capsaicin promotes the release of fat from adipose as well as the burning of fat in muscle tissue via a variety of mechanisms, all of which ultimately result in an increase in metabolism. Given the ability of capsaicin ingestion to improve satiety and fatty acid oxidation, capsaicin ingestion may be used to enhance body composition. The improvement in energy expenditure reported by Lee et al. (2010) equals an additional 25,000 kcal expended per year in a 145 lb individual. If nutrition and exercise is optimized, this would translate into an additional 7 lb reduction in body fat per year.

Finally, capsaicin consumption reduces pro-inflammatory cytokine secretion and also appears to protect against diet-induced reductions in inherent anti-inflammatory systems. Given these results, eating chili peppers may reduce the risk of cancer via inflammation modulation (Surh, 2012).

So, how much do you need to eat to reap these results? While some of the studies have used doses in upwards of 130 mg/day capsaicin (about 75 g of dried chili peppers), improvements in fatty acid oxidation and energy expenditure have been seen with as little as 9 mg/day capsaicinoids. Given that a raw jalapeno pepper contains about 5-10mg of capsaicin (depending on its pungency), I would personally suggest consuming at least 5 jalapeno peppers per day.

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References

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