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

Abstract

Summary 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. Key Words licorice, flavonoid, respiratory exchange ratio, fat oxidation, humans Licorice is widely consumed as a food and natural medicine/herbal drug in both Eastern and Western countries (1). There are several species of licorice, including Glycyrrhiza uralensis Fischer, G. glabra Linne, and G. inflata Batalin, each of which contain specific flavonoids (1).Licorice flavonoid oil (LFO) is a new functional food ingredient containing hydrophobic flavonoids derived from G. glabra (2). Our previous study suggested that LFO is effective in reducing visceral fat accumulation and suppressing elevated blood glucose levels in obese diabetic KK-Ay mice (2). Subsequently, a double-blind placebo-controlled clinical trial showed that LFO was effective in suppressing body weight gain by reducing body fat mass in overweight volunteers (3). These studies indicate that LFO may help to prevent lifestylerelated diseases such as obesity associated with metabolic syndrome. The mechanism of the antiobesity effect of LFO was previously investigated in a high-fat diet-induced obese C57BL/6J mouse model and the results suggest that the effect was mediated by modification of the expression levels of lipid metabolism-related genes in the liver (4). In particular, it has been shown that LFO increases the enzymatic activity of acyl-coA dehydrogenase, the rate-limiting enzyme in the fatty acid oxidative pathway, and simultaneously decreases the enzyme activity of acetyl-coA carboxylase and fatty acid synthase, the rate-limiting enzymes in the fatty acid synthetic pathway.These studies suggest that LFO may alter energy metabolism, especially fat degradation. However, there is no information regarding the short-acting effects of LFO on en...

Pharmacological Effects and Underlying Mechanisms of Licorice-Derived Flavonoids

“…Glabridin reduced the body weight of obese mice by decreasing food intake and increasing energy expenditure [ 206 ]. In addition, licorice flavonoid oil prevented and regulated diet-induced obesity and total body fat in human subjects by restoring the expression levels of the related lipid metabolism [ 207 ]. White adipose tissues are energy depots, whereas brown adipose tissues convert energy to heat via thermogenesis and improve triglyceride clearance and glucose metabolism [ 208 , 209 ].…”

Seaweed Fucoxanthin Supplementation Improves Obesity Parameters in Mild Obese Japanese Subjects

“…These polyphenols enhance hepatic fat metabolism by increasing mitochondrial β-oxidation 3 or by promoting the uptake of free acids into the mitochondria of hepatocytes 4 . Since 2015, similar weight loss claims have also been permitted for pueraria flower isoflavonoids 5 and licorice flavonoids 6 under the Japanese Foods with Function Claims system. Despite weight loss claims being allowed for several polyphenolic compounds, no carotenoids have yet been confirmed to achieve clinical weight loss effects.…”