Effect of Glycaemic index of the diet on salivary cortisol and testosterone levels in females
Emad Al-Dujaili & Sophie Ashmore
There has been great interest in the effect of Glycaemic index (GI) of food on weight reduction, obesity, metabolic syndrome and general well being in women. The majority of research into GI was focussed towards improving blood glucose control in diabetes. Also, favourable changes in blood lipids and some beneficial effect in cancers have been reported. The aim of this pilot study is to investigate the impact of ingesting food with varying GI on salivary cortisol and testosterone levels.
A cross-over design was adopted and 8 healthy female subjects volunteered for the study (2023 years old). The project has received ethical approval by QMUC ethical committee. A diet is said to be of low GI if it has a GI of less than 55, medium GI if it has a GI of 5669, and a high GI if it is 70 or greater. All subjects consumed a low GI or high GI diet for three days each, with a washout period separating the two. Saliva samples at baseline, after the low GI diet, washout period and high GI diet were collected at 4 different times during the day. Salivary cortisol and testosterone concentrations were measured by ELISA methods.
GI was significantly different between the low and high GI diets. No significant difference in cortisol concentration was found on either diet. Significantly more testosterone was produced on the low GI diet compared to basal values (related t-test P=0.05) (see Table below). It was found that lower calories were consumed on the low GI diet compared to the high GI diet and the subjects normal diet was very similar to the high GI diet.
In conclusion, it appears that GI of the diet consumed by females influences a variety of parameters and that a low GI diet might increase salivary testosterone concentrations.