Enhancement of Fat Oxidation by Licorice Flavonoid Oil in Healthy Humans during Light Exercise

J Nutr Sci Vitaminol (Tokyo). 2015;61(5):406-16. doi: 10.3177/jnsv.61.406.


Licorice flavonoid oil (LFO) is a new functional food ingredient consisting of hydrophobic licorice polyphenols in medium-chain triglycerides. Recent studies reported that LFO prevented and ameliorated diet-induced obesity via the regulation of lipid metabolism-related gene expression in the livers of mice and rats, while it reduced body weight in overweight human subjects by reducing total body fat. However, the direct effects of LFO on energy metabolism have not been studied in human subjects. Therefore, we investigated the effects of ingestion of LFO on energy metabolism, including fat oxidation, by measuring body surface temperature under resting conditions and respiratory gas analysis under exercise conditions in healthy humans. We showed that ingestion of a single 600 mg dose of LFO elevated body trunk skin temperature when measured in a slightly cooled air-conditioned room, and increased oxygen consumption and decreased the respiratory exchange ratio as measured by respiratory gas analysis during 40% Vo2max exercise with a cycle ergometer. Furthermore, repeated ingestion of 300 mg of LFO for 8 d decreased respiratory exchange during the recovery period following 40 min of 30% Vo2max exercise on a treadmill. These results suggest that LFO enhances fat oxidation in humans during light exercise.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adipose Tissue / metabolism
  • Adolescent
  • Adult
  • Asian Continental Ancestry Group
  • Body Mass Index
  • Body Weight / drug effects
  • Cross-Over Studies
  • Dose-Response Relationship, Drug
  • Double-Blind Method
  • Exercise*
  • Female
  • Flavonoids / pharmacology*
  • Functional Food
  • Glycyrrhiza / chemistry*
  • Humans
  • Japan
  • Lipid Metabolism / drug effects*
  • Liver / drug effects
  • Liver / metabolism
  • Obesity / drug therapy
  • Oxygen Consumption
  • Plant Oils / pharmacology*
  • Polyphenols / pharmacology*
  • Triglycerides / blood
  • Young Adult


  • Flavonoids
  • Plant Oils
  • Polyphenols
  • Triglycerides