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Evolution of Carbohydrate Digestion Enzymes in Human Populations and their relationship to the Glycaemic Index
All of the major transitions in human evolution involved significant changes in diet. The first use of manufactured stone tool some 2.6 million years ago lead to increased meat. The range expansions associated with the movement of some anatomically modern humans out of Africa will have lead to increased dietary breadth, and the Upper Palaeolithic transition is associated with significant advances in hunting and food processing technologies. However, the Neolithic revolution - when humans first started to domesticate various animal and crop species - almost certainly caused the most dramatic change in dietary composition. Among these changes, a reduction in dietary breadth and a dramatic increase in carbohydrate consumption - particularly starch and, in some populations, lactose - are key elements.
Considerable genetic variation is known to exist in
the expression of some human carbohydrate digestion enzymes,
particularly lactase and salivary amylase. However, the extent to which
genetic variation in the other carbohydrate digestion enzymes
(sucrase-isomaltase, maltase-glucoamylase, pancreatic amylase and
trehalase) has been shaped by natural selection and affects the rate of
digestion of respective substrates, is less well studied.
All
carbohydrate digestion results in the release of glucose in intestinal
lumen, as well as galactose in the case of lactose digestion, and
fructose in the case sucrose digestion. The glycemic index of a
carbohydrate-rich food is a measure of how rapidly it will increase
blood glucose levels, and recent studies suggest that high glycemic
index diets can increase the risk of type 2 diabetes and coronary heart
disease.
The aim of this project is to investigate the evolution of carbohydrate digestion enzymes using genetic data and information on ancestral diets, and to examine the extent to which interindividual differences in glycemic response can be explained by variation in the expression of carbohydrate digestion enzymes.
The PhD will involve secondments to Unilever's Colworth House genomics facilities.
