British Journal of Nutrition

Human and Clinical Nutrition

Glycaemic index and glycaemic load of breakfast predict cognitive function and mood in school children: a randomised controlled trial

Renata Michaa1a2 c1, Peter J. Rogersa3 and Michael Nelsona1a4

a1 Nutritional Sciences Research Division, King's College London, 150 Stamford Street, London SE1 9NH, UK

a2 Harvard School of Public Health, 677 Huntington Avenue, Bldg 3-913, Boston, MA 02 115, USA

a3 Department of Experimental Psychology, University of Bristol, Bristol BS8 1TH, UK

a4 School Food Trust, N9 Moorfoot, Sheffield S1 4PQ, UK


The macronutrient composition of a breakfast that could facilitate performance after an overnight fast remains unclear. As glucose is the brain's major energy source, the interest is in investigating meals differing in their blood glucose-raising potential. Findings vary due to unaccounted differences in glucoregulation, arousal and cortisol secretion. We investigated the effects of meals differing in glycaemic index (GI) and glycaemic load (GL) on cognition and mood in school children. A total of seventy-four school children were matched and randomly allocated either to the high-GL or low-GL group. Within each GL group, children received high-GI and low-GI breakfasts. Cognitive function (CF) and mood were measured 95–140 min after breakfast. Blood glucose and salivary cortisol were measured at baseline, before and after the CF tests. Repeated-measures ANOVA was used to identify differences in CF, mood, glucose and cortisol levels between the breakfasts. Low-GI meals predicted feeling more alert and happy, and less nervous and thirsty (P < 0·05 for each); high-GL meals predicted feeling more confident, and less sluggish, hungry and thirsty (P < 0·05 for each). High-GL (P < 0·001) and high-GI (P = 0·05) meals increased glucose levels 90 min after breakfast, and high-GI meals increased cortisol levels (P < 0·01). When baseline mood, glucose and cortisol levels were considered, low-GI meals predicted better declarative-verbal memory (P = 0·03), and high-GI meals better vigilance (P < 0·03); observed GI effects were valid across GL groups. GI effects on cognition appear to be domain specific. On balance, it would appear that the low-GI high-GL breakfast may help to improve learning, and of potential value in informing government education policies relating to dietary recommendations and implementation concerning breakfast.

(Received November 18 2010)

(Revised March 21 2011)

(Accepted March 23 2011)

(Online publication June 08 2011)


c1 Dr Renata Micha, fax +1 617 566 7805, email;


Abbreviations: CF, cognitive function; GI, glycaemic index; GL, glycaemic load