C ARBOHYDRATES AND P ERFORMANCE IN H EALTHY A DULTS
13.4.2 C ARBOHYDRATES AND P ERFORMANCE IN H EALTHY A DULTS
Table 13.4 summarizes the results of studies investigating the effect of carbohydrate consumption on a variety of performance measures. From this table you can see that there is considerable variation in the macronutrient content of the meals provided in the various studies, as well as the type of tasks chosen and the time of assessment of the effect of the meals. This variation from study to study has certainly contributed to the variation in results across studies. In spite of this, there seem to be some trends emerging. In reviewing the studies 120,121,126–128,133 that have investigated the effect of a carbohydrate load in the morning, typically consumed at breakfast time, it is apparent that most of the studies have investigated some form of reaction time and some type of memory or recall task. These studies have revealed that the consumption of a carbohydrate breakfast either has no effect or slows reaction time. The slowed reaction time seems to occur in tasks requiring speed of reaction fol- lowing some choice decision. Where the measure is some simple measure of speed of reaction without a choice, the carbohydrate breakfast seems to have no effect when compared to breakfasts composed primarily of other macronutrients, such as protein or fat.
When short-term memory is the task, consumption of a carbohydrate breakfast seems to result in worse or slower performance. However, if the memory task involves recall, the type of meal consumed seems to have no effect. While it may seem contradictory that a carbohydrate breakfast would result in worse short-term memory but have no effect on recall, this differential effect is probably due to the type of task involved in what was labeled short-term memory vs. recall. The recall task involved remembering a list of words, whereas the short-term memory task involved recognizing a defined sequence of colored circles.
458 TABLE 13.4
Summary of Studies Investigating the Effect of Carbohydrates on Performance
Study Participants
Meal Type
Outcome Measure
Time of Effect
Outcome Affected
Effect of Carbohydrates on Performance in the Morning
Fischer et al., Male students
Longer decision time, less accurate 2002
CHO rich vs. balanced vs.
Choice reaction time, combined
Before and hourly for 3 h
protein rich at 7 A . M .
short-term memory and
short-term memory, slower central
peripheral attention, task and
reaction time after CHO meal
multitask test
Fischer et al., Male students
Reaction time worse for protein and 2001
CHO vs. protein vs. fat at 7 A . M . Simple and choice reaction time, Before and hourly for 3 h after
combined short-term memory
breakfast
CHO; short-term memory and
and peripheral attention task
focused attention tasks better after fat vs. CHO and protein
Benton et al., Female adults
No meal effect before snack, but 2001
Fast vs. high vs. low CHO at 10 Recall of words presented on a
Before, 15 min and 1 h after
A . M . crossed with snack or no
tape recorder
breakfast, and 15 min and 1 h
better memory 15 min but not 1 h
after CHO snack Lloyd et al., Mostly females Low, medium, and high fat
snack at 11:30
after snack
Visual processing, tapping, recall, Before and at 30, 90, and 150 min No effect of meal type on any of the 1996
performance measures Functional F
crossed with low, medium, and
reaction time
after breakfast
high CHO and no breakfast
Smith et al., Male and female High-CHO vs. high-protein or
No effect on any task 1994
Reaction time, serial response,
Before 8 A . M . or 8:30 breakfast
students
no breakfast
repeated digits
and 1.5 and 2.5 h after breakfast
Smith, 1988 Adults
CHO of cereal and toast or no
Logical reasoning and search task Before, right after, and 1.5 h after No effect on either task ood Carboh
breakfast
breakfast
Effect of Carbohydrates on Performance in the Afternoon
Markus et High- and low- CHO rich vs. protein rich at 11 Memory scanning task
Reaction time in responding faster on al., 1998
1.5 h after lunch and right after
stress-prone
CHO-rich diet ydrates students
A . M . or 1 P . M .
stress induction
Dietar Wells et al., Male adults
Hourly between 9 A . M . and 5 P . M . Response speed faster in low-fat high 1995
High fat, low CHO or low CHO, Sustained attention task
high fat, both with moderate
with lunch at 12:45 P . M .
CHO condition
y Carboh Kelly et al., Male adults
protein
Study 1: High CHO, low CHO, Digit symbol, number recogition, At 9:30, 1:30, and 7 P . M . for both No effect of type of meal on any of 1994
high fat, low fat at lunch; study
repeated acquisition,
studies
the psychomotor tasks
2: high, medium, and low CHO
reinforcement of low-rate
ydrates as Mood and P
and fat at lunch and breakfast
schedule
Spring et al., Male and female High CHO or high protein
2 h after eating breakfast at 7:15 Shadowing less accurate after CHO 1983
Reaction time and dichotic
adults
shadowing
to 8:30 A . M . and 2 h after eating
meal due largely to older individuals
eating a CHO lunch Lloyd et al., Mostly females Low fat, high CHO; medium fat, Visual information processing,
lunch at 11 A . M . and 1 P . M .
30 min before and 30, 90, and 150 Faster reaction time after medium-fat, 1994
medium CHO; high fat, low
tapping, recall, and reaction time min after 12:30 P . M . lunch
medium-CHO lunch
CHO
Deijen et al., Primarily female High-protein food until 1:30 P . M . CPT, pattern comparison, 10:30 A . M . and 6 P . M ., 1.5 to 2h Faster finger tapping and slower er 1989
memory scanning in diet group in students
college
and high-CHO food after 1:30
symbol–digit substitution,
after meal and after being on the
formance Modulators
P . M . or ad libitum diet
memory scanning, finger
diet for 3 weeks
the morning
tapping
Smith et al., Male and female High-protein, high-starch, or
Slower reactions to peripheral stimuli 1988
Focused attention and search test Before and 1.25 h after lunch
after CHO Spring et al., Female adults
adults
high-sugar lunch
meals
No meal effect on any performance 1986
CHO-rich, protein-rich,
Digit–symbol substitution, letter Before and 4 times after lunch
balanced, or no lunch
cancellation, and test of addition
measure
Spring et al., Male adults
Slower reaction time at 1:45 P . M . and 1986
Starch or protein lunch
Auditory reaction time,
Before and hourly for 5 h after
digit–symbol substitution,
noon lunch
impaired digit–symbol substitution
dichotic listening
after CHO lunch
Functional Food Carbohydrates
Many other performance tasks were used as outcome measures, ranging from visual processing tasks to logical reasoning tasks. The studies did not demonstrate any meal effect on any of these tasks. Therefore, to date, there seems to be little effect of consumption of a carbohydrate breakfast relative to consumption of either
a protein or high-fat breakfast on most of the performance measures investigated. This does not mean that consumption of breakfast does not affect performance, but only that consumption of a carbohydrate-rich breakfast seems to have little beneficial or detrimental effect compared with a protein-rich or fat-rich breakfast, at least on the performance tasks currently investigated.
The studies 124,131,136,138–141 that have investigated the effect of consuming a car- bohydrate-rich meal at lunchtime have produced a mixed bag, probably due to the variation in types of tasks investigated. Perhaps the most consistent finding is that consumption of a carbohydrate-rich lunch results in faster speed of responding to a task that requires some type of sustained attention. However, there may be a slower reaction time to an auditory attention task as well as to stimuli seen in the periphery of the visual field. There seems to be no effect of consumption of carbohydrates on tasks such as number recognition, digit–symbol substitution, addition, or letter cancellation.