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Breakfast glycemic index and exercise: Combined effects on adolescents' cognition

Abstract: The aim of the present study was to examine the combined effects of breakfast glycaemic index (GI) and a mid-morning bout of exercise on adolescents' cognitive function.

Participants were randomly allocated to a high or low GI breakfast group in a mixed research design, where each participant completed two experimental trials (exercise and resting). Forty-two adolescents (12.4 ± 0.5 years old), undertook a bout of exercise (ten repeats of level one of the multi-stage fitness test; exercise trial) or continued to rest (resting trial) following consumption of either a high or low GI breakfast. A battery of cognitive function tests (visual search test, Stroop test and Sternberg paradigm) was completed 30 min before and 45 min following the exercise.

Average heart rate during exercise was 170 ± 15 beats·min− 1. On the complex level of the Stroop test, response times improved across the morning following the low GI breakfast on both the exercise and resting trials, though the improvement was greatest on the exercise trial. However, response times only improved on the resting trial following the high GI breakfast (p = 0.012). On the 5 letter level of the Sternberg paradigm, response times improved across the morning following the low GI breakfast (regardless of exercise) and only on the exercise trial following the high GI breakfast (p = 0.019).

The findings of the present study suggest that the combined effects of breakfast GI and exercise in adolescents depend upon the component of cognitive function examined. A low GI breakfast and mid-morning bout of exercise were individually beneficial for response times on the Sternberg paradigm, whereas they conferred additional benefits for response times on the Stroop test.


Alex’s Notes: There are many persons who still believe that breakfast is king, despite it being shown to have no benefits towards weight loss or cognitive performance. My personal take on the matter is that breakfast is by no means necessary (speaking about the traditional morning meal here, as technically the first meal of the day will break the fast no matter what time it is consumed), but if you enjoy breakfast then by all means continue eating it. Breakfast isn’t always consumed in isolation, however, and often comparisons are confounded by unequal calories and/or nutritional content.

With the above in mind, the current study sought to assess the impact of high- and low-glycemic index (GI) breakfasts alone or in combination with a short bout of exercise on three markers of cognitive performance in adolescents. To this end, 42 participants aged 11-13 years were randomly allocated to a high or low GI breakfast group. Within each group, the participants completed two trials separated by seven days: and exercise or rest condition. Before all this, the subjects completed a familiarization session where they could complete the cognitive tests until comfortable with them to eliminate any potential learning effects.

The breakfasts of the high and low GI groups appear in the table below. Why the researchers used margarine is beyond me. The exercise consisted of a ten repetition shuttle-run where each repetition consisted of 7x20m shuttle-runs separated by 30 seconds of rest. The entire thing took about ten minutes.







White bread






1% fat milk










Total energy

422 kcal

420 kcal










Glycemic Index



Glycemic Load



Three cognitive function tests were used: the Stroop Test to assess executive function & selective attention, the Sternberg Paradigm to assess working memory, and the Visual Search Test to assess perception and simple response times. Additionally, a mood questionnaire was administered to assess energy, tiredness, tension, and calmness, and visual analogue scales (VAS) were used to assess hunger, fullness, and concentration.

So what happened?

After an overnight fast, the participants arrived at the school to begin the experimental trial. Breakfast was consumed at time=0 and had to be finished within 15 minutes. The cognitive function tests were then started at t=30 minutes, followed by exercise at t=60 minutes. The cognitive tests were then re-administered at t=120 minutes. Blood samples were collected and mood questionnaires and VAS scales collected at time points 0, 30, 60, and 120 minutes.

As would be expected, plasma glucose and insulin concentrations were greater following the high-GI breakfast compared to the low-GI breakfast regardless of exercise. For the low-GI breakfast, glucose and insulin levels were not different between exercise and resting conditions, whereas following the high-GI breakfast, glucose and insulin were significantly greater in the exercise condition at 120 minutes compared to the resting condition, with no differences before then.

There were no differences between the GI groups for any aspect of exercise performance, mood, hunger, fullness, or concentration before or after exercise. In both groups, energy, fullness, and concentration increased, while tiredness, tension, calmness, and hunger decreased following breakfast (t=30 min), all of which returned to baseline by 120 minutes.

There was no interaction of any condition with the participants’ accuracy on the three cognition tests. In fact, the only significant differences between conditions were related to response times on the most difficult portions of the tests. You can see the results in the table below.


Stroop Test

Sternberg Paradigm

Visual Search Test

Greatest Improvement

Least Improvement

Low-GI / Exercise

High-GI / Rest

Low-GI / Rest

High-GI / Exercise

High-GI / Exercise

Low-GI / Rest

Low-GI / Exercise

High-GI / Rest

No differences

I want to emphasize that these results were only for the most difficult portions of the tests with regard to response time. On the easier portions and on test accuracy there were no interactions of any condition.

Bottom line

If anything, this study supports the idea that different breakfast compositions affect aspects of cognitive performance differently. This becomes truer when considered with exercise. Aside from this, there are many questions left unanswered. A previous meta-analysis found no benefit of breakfast consumption in general on cognitive performance, and it would have been interesting to see how a no breakfast with or without exercise compared to the high and low-GI breakfasts. Similarly, what if the breakfast was predominantly protein and/or fat?


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