The trial studied the benefits of Dioscorea esculenta, also known as lesser yam, produced in Okinawa.
Writing in Nutrients, the researchers from Ritsumeikan University said that lesser yam has shown to improve glycaemic control in diabetic rats and increase muscle mass in athletes.
Diosgenin is the bioactive component in lesser yam.
A 2020 study published in Journal of Clinical Biochemistry and Nutrition showed that taking Dioscorea esculenta tablet at 2000 mg/day combined with resistance exercise for eight weeks have increased muscle mass and strength in athletes.
The present study seeks to find out if it could benefit muscle quantity, quality, and glycaemic control index in the middle-aged adults.
A total of 66 healthy individuals in their 40s to 50s were randomised into four groups for the study.
They took either 1) the placebo without undergoing resistance training or 2) Dioscorea esculenta without undergoing resistance training or 3) the placebo and underwent resistance training or 4) Dioscorea esculenta and underwent resistance training.
The resistance training consists of using elastic brands for three days per week, while Dioscorea esculenta tablets were ingested at 2000 mg/day within 30 minutes of dinner.
The study was funded by Okinawa Television Development (OTV) which also runs a Healthcare business.
The firm has been studying the benefits of locally grown Okinawa sweet potatoes and has announced plans to develop products sold under the brand name LeQom.
Findings showed that Dioscorea esculenta intake combined with resistance exercise had improved muscle thickness.
There was a significant increase in both anterior and posterior femoris muscle thickness as compared to the group taking placebo and not undergoing resistance training.
They also used a significantly shorter time in accomplishing the “Five Times to Stand Test” as compared to the placebo group not undergoing resistance training.
“In the present study, 12-week Dioscorea esculenta intake combined with low-intensity resistance exercise in healthy middle-aged and older adults resulted in greater femoris muscle thickness and a faster test of five times sit-to-stand (an index of muscle function) than that associated with sedentary participants with placebo intake, though low-intensity resistance exercise alone did not clearly affect them,” said the researchers.
In addition, Dioscorea esculenta supplementation and resistance training had significantly lowered the percentage of glycated haemoglobin (HbA1C) as compared to the group taking placebo and not undergoing resistance training.
“The supply of diosgenin abundantly present in Dioscorea esculenta may promote glucose metabolism and the utilisation of the skeletal muscle through assisting the secretion of sex steroid hormones in the skeletal muscle, resulting in a decrease in HbA1c,” the researchers explained.
Dioscorea Esculenta Intake with Resistance Training Improves Muscle Quantity and Quality in Healthy Middle-Aged and Older Adults: A Randomized Controlled Trial
Authors: Iemitsu, K.; Fujie, S.; Uchida, M.; Inoue, K.; Shinohara, Y.; Iemitsu, M.