Acute p-synephrine ingestion increases whole-body fat oxidation during 1-h of cycling at Fatmax



p-Synephrine, the principal alkaloid of bitter orange (Citrus aurantium), is widely used in dietary supplements for weight loss due to its purported effect of increasing fat oxidation. However, there is a paucity of scientific information about its effectiveness in enhancing fat oxidation during exercise. The aim of this investigation was to determine the effect of an acute dose of p-synephrine on substrate oxidation during prolonged and constant intensity exercise.


In a double-blind and randomized experiment, 14 healthy subjects performed two acute experimental trials after ingesting either p-synephrine (3 mg kg−1) or a placebo (cellulose). Energy expenditure and fat oxidation rates were continuously measured by indirect calorimetry during 1 h of continuous cycling at Fatmax, the intensity that induces maximal fat oxidation rate.


In comparison to the placebo, energy expenditure during 1 h of cycling remained unchanged with p-synephrine (698 ± 129 vs. 686 ± 123 kcal, P = 0.08). However, p-synephrine increased whole-body fat oxidation (33.6 ± 10.4 vs. 37.3 ± 9.8 g, P < 0.01) while also reducing carbohydrate oxidation (99.5 ± 30.4 vs. 85.0 ± 28.4 g, P < 0.01). However, the magnitude of the shift on substrate oxidation induced by p-synephrine was small.


Acute ingestion of p-synephrine augments fat oxidation during prolonged and constant-intensity exercise.

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The authors would like to thank the subjects for their invaluable contribution to the study.


This investigation did not receive any funding.

Author information




Jorge Gutiérrez-Hellín1,2,3,4,5, Carlos Ruiz-Moreno1,2,3,6 and Juan Del Coso1,2,3,4,6. 1. Formulated the research question. 2. Designed the study. 3. Conducted it. 4. Analyzed the data. 5. Wrote the article. 6. Revised the article.

Corresponding author

Correspondence to Juan Del Coso.

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All authors declare: no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous 3 years; no other relationships or activities that would appear to have influenced the submitted work.

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Gutiérrez-Hellín, J., Ruiz-Moreno, C. & Del Coso, J. Acute p-synephrine ingestion increases whole-body fat oxidation during 1-h of cycling at Fatmax. Eur J Nutr 59, 3341–3345 (2020).

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  • Nutrition supplement
  • Exercise
  • Citrus aurantium
  • Bitter orange
  • Maximal fat oxidation