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.