The glycemic index is a measure of the effects of carbohydrates in food on blood sugar levels and GI levels can vary from low (55 or less), medium (56-69) and high (70 and above).
Researchers from the International Rice Research Institute (IRRI) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) identified the Waxy gene (Wx gene) as the major gene associated with GI variations in the rice samples.
GI levels were also found to be associated with amylose content (a starch component) with increasing amylose content leading to decreased values of GI.
The study Identification of a Major Genetic Determinany of Glycaemic Index in Rice analysed 235 global rice types to assess the GI levels. Natural and improved rice samples were analysed including indica and tropical and temperate japonica rices.
“Strong correlations between amylose content, the Waxy locus and GI were observed across all samples,” the researchers wrote.
“Until recently, the nutritional potential of rice has not been a target of rice improvement programmes, and while various countries would like to develop low-GI rices, the limitation lies in the selecting for the trait.”
“This paper reports the first large-scale phenotyping of this trait,” they said.
“Ultimately it provides a mechanism for breeding programmes to select for GI based on amylose content,” they continued.
This is “an important achievement that offers rice breeders the opportunity to develop varieties with different GI levels to meet consumer demands”, the researchers said.
“Future development of low-GI rice would also enable food manufacturers to develop new, low-GI food products based on rice,” they added.
Rice important in curbing chronic disease
The study marks part of a wider research commitment to investigate the role of rice in mitigating chronic diseases such as type-2 diabetes.
Dr Tony Bird, researcher at CSIRO Food Futures Flagship, said: “Low-GI diets can reduce the likelihood of developing type-2 diabetes, and are also useful for helping diabetics better manage their condition.”
The research is “good news” for diabetics or those at risk of diabetes looking to control their condition through diet, Bird said.
According to the International Diabetes Federation, incident rates of diabetes will rise from 240m in 2007 to 380m in 2025, with 60% coming from Asia.
2011 issue, Volume 4, number 2, pages 66-74
"Identification of a Major Genetic Determinant of Glycaemic Index in Rice"
Authors: M. A. Fitzgerald, S. Rahman, A. P. Resurreccion et al.