title: Acute p-synephrine ingestion increases fat oxidation rate during exercise.
abstract: 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.
  
  
  
  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.
  
  
  
  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).
  
  
  
  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.
authors.affiliation: Exercise Physiology Laboratory, Sport Science Institute, Camilo José Cela University, Madrid, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Gutiérrez-Hellín
authors.affiliation: Exercise Physiology Laboratory, Sport Science Institute, Camilo José Cela University, Madrid, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Del Coso
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D019587:Dietary Supplements; D004311:Double-Blind Method; D004734:Energy Metabolism / Q000187:drug effects*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D010084:Oxidation-Reduction; D013578:Synephrine / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D013578:Synephrine
keywords: Citrus aurantium; bitter orange; fat metabolism; nutrition; stimulant