Animal Researchsection" id="stimulation-of-adrenoceptors">Stimulation of adrenoceptorsrong>Bitter orange extract may be safe and effective at burning fat, but more research is needed.
Bitter orange is a citrus fruit used to make an extract with proposed fat-burning properties. Bitter orange may promote weight loss by:
- Boosting metabolism. Bitter orange extract appears to to trigger thermogenesis (heat production) and lipolysis (the breakdown of fat).
- Suppressing appetite. Animal studies have shown that the aromatic chemicals in bitter orange may have a subtle appetite-suppressing effect.
Bitter orange refers to the citrus fruit from the Citrus aurantium tree species grown throughout the world. Practitioners of traditional Chinese medicine and indigenous tribes of the Amazon have used bitter orange for centuries to treat indigestion, nausea, and constipation.
Today, bitter orange is used to produce oil, cosmetics products, and food flavoring, but is best known as an ingredient in weight loss supplements.1 The main ingredient responsible for the claimed weight loss benefits of bitter orange extract is synephrine, a compound similar in structure and effect to ephedrine found in the herb ephedra.
Since the FDA banned ephedra after linking it to incidents of strokes and heart attacks, many supplement manufacturers have begun substituting ephedrine with synephrine.
Synephrine is considered a sympathetic adrenergic agonist — a compound that stimulates adrenergic receptors found in most cells. In particular, synephrine appears to have a special affinity for alpha one adrenergic receptors, which regulate appetite, and beta three receptors, which control metabolic rate.4
When synephrine binds to beta three receptors, it appears to trigger lipolysis (the burning of fat) by releasing the enzyme adenylyl cyclase. 5 In addition, it also increases the body’s thermogenesis — generation of heat. These effects result in increased metabolic rate (more calories being burned).
Meanwhile when it binds to alpha one receptors, synephrine is believed to suppress appetite, although this effect is minor and requires further research.
Bitter Orange’s Fat Burning BenefitsBitter orange extract is a popular thermogenic weight loss supplement. Although more studies looking specifically at bitter orange extract and synephrine rather than multi-ingredient formulas are needed, current research evidence supports the claim that bitter orange helps you burn fat by boosting metabolism and possibly suppressing appetite.
And despite its negative association with ephedra, clinical trials have failed to identify any significant side effects of bitter orange extract.
Animal studies have shown that bitter orange extract or isolated synephrine are capable of reducing body weight. In particular:
- Mice given CA extract and synephrine for 28 days saw a reduction in body weight gain6
Human ResearchThe majority of studies using bitter orange extract looked at multi-ingredient supplements which make it difficult to isolate the actions of bitter orange alone. On the other hand, only a few studies have examined bitter orange extract by itself.
This randomized, double-blind, placebo controlled study assessed the thermogenic effects of synephrine from Bitter Orange alone versus synephrine combined with the flavonoids naringin and hesperidin. Treatments groups of 10 people each were given either synephrine alone, synephrine plus naringin and hesperdin, or a placebo, in V8 juice.
The major finding was that groups receiving synephrine alone and in combination with the flavonoids showed significant increase in metabolic rate 75 minutes after ingestion.
- The researchers concluded that “…a thermogenic combination of ingredients that elevated metabolic rates without corresponding elevations in blood pressure and heart-rates warrants longer term studies to assess its value as a weight control agent“7
This study examined the influence of citrus aurantium (CA) extract containing 26 mg synephrine on metabolic rate – the rate at which the body burns calories. Thirty participants had the thermic effect of food (TEF) — the amount of energy used for digestion — tested with and without CA. CA was found to increase the body’s resting energy expenditure for up to four hours after consumption. When used with food, CA only increased the TEF in women.
- The researchers concluded that “…this acute response may not translate into a chronic effect or a clinically significant weight loss over time“8
Most studies of bitter orange extract have looked at patented, multi-ingredient weight loss formulas that add compounds such as caffeine. These studies suggest that supplements containing synephrine as the main ingredient are safe and effective at increasing the body’s resting metabolic rate and energy expenditure, and result in a subsequent improvement of weight loss.
But despite these positive results, the studies are limited by their short duration (6-12 weeks) and the difficulty of isolating the effects of bitter orange extract/synephrine.9
Dosage for Fat Burning
Supplements in Review Says
Bitter orange appears to promote fat loss by boosting metabolism. While more high-quality, long-duration research is needed, there is evidence that bitter orange extract helps with weight loss.
Standardized extract appears to be the ideal form. Since most studies use extract that contains a certain amount of synephrine, it’s best to look for standardized bitter orange extracts.
- Bitter Orange. National Center for Complementary and Integrative Health. Apr 2012. ↩
- Shara M et al. Cardiovascular Safety of Oral p-Synephrine (Bitter Orange) in Healthy Subjects: A Randomized Placebo-Controlled Cross-over Clinical Trial. Phytother Res. 2016 May;30(5):842-7. ↩
- Kaats GR et al. A 60day double-blind, placebo-controlled safety study involving Citrus aurantium (bitter orange) extract. Food Chem Toxicol. 2013 May;55:358-62. ↩
- Stohs SJ, et al. A Review of the Receptor-Binding Properties of p-Synephrine as Related to Its Pharmacological Effects.Oxidative Medicine and Cellular Longevity. Volume 2011. ↩
- Arch JR beta(3)-Adrenoceptor agonists: potential, pitfalls and progress . Eur J Pharmacol. 2002. ↩
- Arbo MD et al. Subchronic toxicity of Citrus aurantium L. (Rutaceae) extract and p-synephrine in mice. Regul Toxicol Pharmacol. 2009 Jul;54(2):114-7. ↩
- Stohs SJ, et al Effects of p-synephrine alone and in combination with selected bioflavonoids on resting metabolism, blood pressure, heart rate and self-reported mood changes . Int J Med Sci. 2011. ↩
- Gougeon R, et al. Increase in the thermic effect of food in women by adrenergic amines extracted from citrus aurantium. Obes Res. 2005 Jul;13(7):1187-94. ↩
- Stohs AJ et al. A Review of the Human Clinical Studies Involving Citrus aurantium (Bitter Orange) Extract and its Primary Protoalkaloid p-Synephrine. Int J Med Sci. 2012; 9(7): 527–538. ↩