THESIS

6.4.4 Low GI diet on cognitive performance
The Academic Press Dictionary of Science and technology defined
cognition as ‘the mental activity by which an individual is aware of and knows about
his or her environment, including such processes as perceiving, remembering,
reasoning, judging and problem solving’. The brain uses glucose as a main source of
energy. Glycogen brain becomes important only in any metabolic state where supply
transiently cannot meet demand. Such conditions could occur during prolonged focal
activation, sleep deprivation, seizures, and mild hypoxia (Gruetter, 2003).
Under normal circumstances, the brain depends on a continuous
supply of glucose from blood. In adult humans, the brain oxidizes about 120 g of
glucose per day. In general, cognitive performance tasks can be used to examine a
number of skills or abilities concerning the following functions: perception, memory,
attention, arousal, information processing accuracy and speed of movement. Each
function can be evaluated using specialized tests (Bellisle et al. 1998). A number of
studies performed in adults, beginning with the Iowa breakfast studies, have
demonstrated that missing breakfast can have detrimental effects on performance in
terms of reaction-time tasks, spatial memory and immediate word recall (Benton,
1992). While some aspects of memory seem to be susceptible to the effects of missing
breakfast, other aspects of performance are not affected (Smith et al. 1994). Studies in
children and in adolescents have clearly shown deficits in a wide range of
performance tasks following omission of breakfast, with greater effects in under and
malnourished children. A number of studies have shown that breakfast vs. no
breakfast or high- vs. low-energy breakfast causes changes in sustained attention,
reaction time and memory. Energy improves performance in all of these and may be
related to blood glucose levels, with high-carbohydrate meals producing the best
effects (Bellisle et al. 1998). A recent literature review concluded that the
enhancement of cognitive function by incrementing systemic glucose is limited to
relatively complex tasks, and not easy tasks (Benton, 2001).
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