Synephrine – alkaloid, known as a termegonic found mainly in the bitter orange zest (Citrus aurantium) replaced ephedryne which has been banned due to health risks, is mainly using by athlets to increase their fat loss but does it really work?
Sciencific research review will help to shed more light on this biogenic amine.
Let’s start with this research, which cleary shows synephrine effects.
Dose-Response Effects of p-Synephrine on Fat Oxidation Rate During Exercise of Increasing Intensity
„The aim of this investigation was to determine the effects different doses of p-synephrine on maximal fat oxidation during exercise. Seventeen healthy subjects volunteered to participate in a double-blind and randomised experimental design composed of four identical experimental trials. On four trials separated by 72 h, participants ingested a placebo or 1, 2 or 3 mg/kg of p-synephrine. After resting for 60 min to allow substance absorption, participants performed an exercise test of increasing intensity on a cycle ergometer while gas exchange was measured continuously. None of the doses of p-synephrine affected energy expenditure or heart rates during the test. The highest rate of fat oxidation with the placebo (0.35 ± 0.05 g/min) was reached at 38.0 ± 1.9% of VO2max . The ingestion of 1 mg/kg increased maximal fat oxidation to 0.47 ± 0.11 g/min (p = 0.01) but did not change the intensity at which it was obtained (42.0 ± 9.4% of VO2max ). The ingestion of 2 and 3 mg/kg of p-synephrine increased maximal fat oxidation to 0.55 ± 0.14 g/min (p < 0.01), although only 3 mg/kg slightly changed the intensity at which it was obtained (43.0 ± 9.5% of VO2max , p < 0.01). In conclusion, although all p-synephrine increased the maximal rate of fat oxidation during exercise, the highest effects were found with 2 and 3 mg/kg.” Gutiérrez-Hellín J, Del Coso J.. Phytother Res. 2018 Feb;32(2):370-374. doi: 10.1002/ptr.5937. Epub 2017 Oct 11. PMID: 29024325.
Acute p-synephrine ingestion increases fat oxidation rate during exercise.
„Aims: p-Synephrine is a protoalkaloid widely used in dietary supplements for weight management because of its purported thermogenic effects. However, there is a lack of scientific information about its effectiveness to increase fat metabolism during exercise. The purpose of this investigation was to determine the effects of an acute ingestion of p-synephrine on fat oxidation at rest and during exercise.
Methods: In a double-blind, randomized and counterbalanced experimental design, 18 healthy subjects performed two acute experimental trials after the ingestion of p-synephrine (3 mg kg(-1) ) or after the ingestion of a placebo (cellulose). Energy expenditure and fat oxidation rates were measured by indirect calorimetry at rest and during a cycle ergometer ramp exercise test (increases of 25 W every 3 min) until volitional fatigue.
Results: In comparison with the placebo, the ingestion of p-synephrine did not change energy consumption (1.6 ± 0.3 vs. 1.6 ± 0.3 kcal min(-1) ; P = 0.69) or fat oxidation rate at rest (0.08 ± 0.02 vs. 0.10 ± 0.04 g min(-1) ; P = 0.15). However, the intake of p-synephrine moved the fat oxidation-exercise intensity curve upwards during the incremental exercise (P < 0.05) without affecting energy expenditure. Moreover, p-synephrine increased maximal fat oxidation rate (0.29 ± 0.15 vs. 0.40 ± 0.18 g min(-1) ; P = 0.01) during exercise although it did not affect the intensity at which maximal fat oxidation was achieved (55.8 ± 7.7 vs. 56.7 ± 8.2% VO2peak ; P = 0.51).
Conclusions: The acute ingestion of p-synephrine increased the fat oxidation rate while it reduced the carbohydrate oxidation rate when exercising at low-to-moderate exercise intensities.” Gutiérrez-Hellín J, Del Coso J. Br J Clin Pharmacol. 2016 Aug;82(2):362-8. doi: 10.1111/bcp.12952. Epub 2016 May 7. PMID: 27038225; PMCID: PMC4972152.
Following by combination with caffeine which may increase the fat loss.
The Effects of Supplementation with p-Synephrine Alone and in Combination with Caffeine on Metabolic, Lipolytic, and Cardiovascular Responses during Resistance Exercise.
Objective: „The purpose of this study was to examine the metabolic, lipolytic, and cardiovascular responses to supplementation with p-synephrine alone and in combination with caffeine during resistance exercise (RE)”
Metods: „Twelve healthy men performed a control RE protocol (6 × 10 repetitions of squats) and were randomly assigned (using a double-blind crossover design with random protocol sequencing) to a supplement sequence: p-synephrine (S; 100 mg), p-synephrine + caffeine (SCF; 100 mg of p-synephrine plus 100 mg of caffeine), or a placebo (P). Subjects reported to the lab at a standard time, consumed a supplement, sat quietly for 45 minutes, performed the RE protocol, and sat quietly for 30 minutes. Blood samples were collected at rest (T1), after sitting quietly for 45 minutes (T2), immediately following RE (T3), and 15 minutes (T4) and 30 minutes (T5) postexercise. Oxygen consumption (VO2) and heart rate (HR) data were collected throughout.”
Results: „Serum glycerol was significantly elevated at T2 only in S and SCF and T3 to T5 in all treatments. Nonesterified fatty acid (NEFA) concentrations did not differ between treatments. Plasma glucose was significantly elevated compared to T1 with highest area under the curve values seen in SCF. Mean VO2 and energy expenditure (EE) were significantly higher in S and SCF through 30 minutes postexercise. Fat oxidation rates favored S and SCF between 25 and 30 minutes postexercise. Mean HR during RE was significantly highest in SCF.”
Conclusion: „Supplementation with S and SCF increases lipolysis primarily at rest and increases VO2, EE, and fat oxidation rates 30 minutes following RE. No HR changes were observed unless caffeine was added.” Ratamess NA, Bush JA, Kang J, Kraemer WJ, Stohs SJ, Nocera VG, Leise MD, Diamond KB, Campbell SC, Miller HB, Faigenbaum AD.. J Am Coll Nutr. 2016 Nov-Dec;35(8):657-669. doi: 10.1080/07315724.2016.1150223. Epub 2016 Aug 2. PMID: 27484437.
Also let’s have a look at its side effects which may occur.
Effect of acute administration of an herbal preparation on blood pressure and heart rate in humans
„Confusion and controversy exist regarding the cardiovascular effects of dietary supplements containing caffeine and Citrus aurantium (bitter orange) extract. The primary protoalkaloidal ingredient in bitter orange extract is p-synephrine which has some structural similarities to ephedrine and nor-epinephrine, but exhibits markedly different pharmacokinetic and receptor binding properties. The goal of this study was to investigate the cardiovascular effects of a product containing caffeine, bitter orange extract (p-synephrine) and green tea extract in mildly overweight individuals. Fourteen female and nine male subjects (age 24.7 ±7.4 yrs, BMI: 26.6 ±3.8) volunteered in this randomized, placebo-controlled, crossover, double-blind designed study. On day one, subjects entered the laboratory following an overnight fast. Heart rate and blood pressure were recorded at 60 min. Expired air was analyzed for the next 10 min of the session. At each of three meals, subjects ingested one capsule that was either a non-caloric placebo or a dietary supplement that contained 13 mg p-synephrine and 176 mg caffeine. On the following day, the subjects returned and repeated the protocol for data collection beginning 60 min after consuming one capsule of the placebo or the dietary supplement. No effects of the dietary supplement on heart rate, systolic and diastolic blood pressure or mean arterial pressure were observed. No between or within group differences were observed when data were analyzed for gender and caffeine usage. A small but significant decrease in resting respiratory exchange ratio was observed for the low caffeine user group in response to the product containing caffeine and p-synephrine. The results of this study indicate that ingestion of a product containing bitter orange extract, caffeine and green tea extract does not lead to increased cardiovascular stress and that fat oxidation may increase in certain populations.” Seifert JG, Nelson A, Devonish J, Burke ER, Stohs SJ. Int J Med Sci. 2011 Mar 2;8(3):192-7. doi: 10.7150/ijms.8.192. PMID: 21448304; PMCID: PMC3053490.
Effects of p-synephrine alone and in combination with selected bioflavonoids on resting metabolism, blood pressure, heart rate and self-reported mood changes.
Abstract
Bitter orange (Citrus aurantium) extract is widely used in dietary supplements for weight management and sports performance. Its primary protoalkaloid is p-synephrine. Most studies involving bitter orange extract and p-synephrine have used products with multiple ingredients. The current study assessed the thermogenic effects of p-synephrine alone and in conjunction with the flavonoids naringin and hesperidin in a double-blinded, randomized, placebo-controlled protocol with 10 subjects per treatment group. Resting metabolic rates (RMR), blood pressure, heart rates and a self-reported rating scale were determined at baseline and 75 min after oral ingestion of the test products in V-8 juice. A decrease of 30 kcal occurred in the placebo control relative to baseline. The group receiving p-synephrine (50 mg) alone exhibited a 65 kcal increase in RMR as compared to the placebo group. The consumption of 600 mg naringin with 50 mg p-synephrine resulted in a 129 kcal increase in RMR relative to the placebo group. In the group receiving 100 mg hesperidin in addition to the 50 mg p-synephrine plus 600 mg naringin, the RMR increased by 183 kcal, an increase that was statistically significant with respect to the placebo control (p<0.02). However, consuming 1000 mg hesperidin with 50 mg p-synephrine plus 600 mg naringin resulted in a RMR that was only 79 kcal greater than the placebo group. None of the treatment groups exhibited changes in heart rate or blood pressure relative to the control group, nor there were no differences in self-reported ratings of 10 symptoms between the treatment groups and the control group. This unusual finding of 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. „ Stohs SJ, Preuss HG, Keith SC, Keith PL, Miller H, Kaats GR. Int J Med Sci. 2011 Apr 28;8(4):295-301. doi: 10.7150/ijms.8.295. PMID: 21537493; PMCID: PMC3085176.
My opinion
Based on these studies, I can only express my subjective opinion when it comes to fat oxidation in which I can not clearly say whether it had an impact on its burning, however, in my opinion, this supplement may have had an effect on the increase in blood pressure and heart rate. However, it should also be taken into account that I used it during high temperature conditions in the midle of the summer, which could also have an impact on these effects.
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