Vol.3, No.6, 383-393 (2011)
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Influences of protein to energy ratios in breakfast
on mood, alertness and attention in the healthy
undergraduate students
Yao-Chi Zeng1*, Shun-Min Li1, Guo-Liang Xiong1, Hui-Min Su2, Jian-Cheng Wan3
1Shenzhen Traditional Chinese Medicine Hospital, Shenzhen, China; *Corresponding Author: 0731zyc@163.com
2Shenzhen Bao’an Maternal and Child Health Hospital, Shenzhen, China;
3Guangzhou University of Traditional Chinese Medicine, Guangzhou, China.
Received 12 February 2011; revised 17 March 2011; accepted 6 May 2011.
Background: The high protein (HP) breakfast
reduced gastric emptying and the most satiat-
ing macronutrient appears to be dietary protein.
Few studies have investigated the effects of
protein to energy ratio in breakfast on mood,
alertness and attention. Objective: This study
was designed to investigate whether the HP
breakfast is more beneficial to mood, alertness
and attention of the healthy undergraduate
student than adequate-protein (AP) breakfast
through the rising body temperature and re-
maining stable blood glucose or through other
physiologic processes. Methods: Thirteen
healthy male undergraduate students (18 - 23 y)
were studied in a double-blind, randomized
crossover design. Blood samples, body tem-
perature, satiety, mood and Continuous Per-
formance Test (CPT) were assessed after the
consumption of two isocaloric breakfasts that
differed in their protein and carbohydrate con-
tent: an HP breakfast (50%, 30%, and 20% of
energy from protein, carbohydrate, and fat, re-
spectively) or an AP breakfast (10%, 70%, and
20% of energy from protein, carbohydrate, and
fat, respectively). Results: Consumption of an
HP breakfast resulted in more steady glucose
and insulin than AP breakfast consumption (p <
0.05). Satiety sc ores and body tem perat ure were
higher af ter HP breakfas t consumpt ion (p < 0.05).
And most import ant, the positiv e mood and CPT
scores w ere higher after HP breakfast than after
AP breakfast intake (p < 0.05). Conclusion: HP
breakfast can effectively stabilize postprandial
serum glucose concentration and elevate post-
prandial temperature of healthy male under-
graduate students. Our present findings dem-
onstrate the relationship between HP breakfast
and mood, alertness and attention. This study
indicated th at HP brea kfast may enhance hum an
performance probably by increasing the thermic
effect of a food and elevating body temperature.
Keywords: Protein; Body Temperature; Mood;
Alertness; Attention
It is widely believed that there exists a strong rela-
tionship between eating and mood, and that diet and
particular dietary constituents can have important influ-
ences on behaviour, including alertness and mental per-
formance[1-3]. Wurtman RJ and Wurtman JJ [1] devel-
oped the hypothesis that carbohydrates can relieve de-
pression because that carbohydrate intake enhanced se-
rotonin synthesis. Their major theory was that a meal
high in carbohydrate increased the rate that tryptophan
entered the brain, leading to an increase in the level of
the neurotransmitter serotonin that modulates mood. As
for fat, it is thought that in many countries current popu-
lation intakes of the n-3 long-chain PUFA (LCPUFA;
also known as long chain omega-3 fatty acids) EPA and
DHA are lower than optimal for a variety of health out-
comes [2,4]. However, Peter J. Rogers’ [5] studies that
have shown substantially increasing EPA and DHA in-
take for 3 months was found not to have beneficial or
harmful effects on mood in mild to moderate depression.
With respect to energy expenditure, it is known that pro-
tein has the highest and most prolonged thermic effect of
the separate macronutrients (20 - 30%), followed by
carbohydrate (5 - 15%) and fat (0 - 3%)[3]. Protein has
been observed to increase satiety to a greater extent than
carbohydrate and fat and therefore can reduce energy
intake [6,7]. Now many positive outcomes associated
with increased dietary protein are thought to be due pri-
Y. C. Zeng et al. / Health 3 (2011) 383-393
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
marily to lower energy intake associated with increased
satiety [8-11], reduced energy efficiency and/or in-
creased thermogenesis [5,12,13], positive effects on
body composition, specifically lean muscle mass[14-16],
and enhanced glycemic control [16,17]. In addition, sev-
eral studies showed that eating breakfast can improve
cognitive performance and attention-concentration
compared with omitting breakfast [18-20], but the effect
of each macronutrient was not defined because of vari-
ous methodologic issues. In fact, the study [21] about the
relationship of macronutrients and memory performance
indicated all of the macronutrients improved paragraph
recall 15 min after ingestion, suggesting that energy in-
take can enhance specific aspects of cognition, in addi-
tion to the effects of energy ingestion on memory, each
macronutrient enhanced performance on various tasks,
possibly via unique mechanisms. Indeed, all three kinds
of macronutrients led to an initial, robust improvement
on delayed paragraph recall. Each macronutrient may
exert different effects on cognition by additional, unique
mechanisms [21]. Human beings should not ingest pure
protein, carbohydrate, or fat, but should pay attention to
the content of the various macronutrients reasonably
matched. However, there is little support for the influ-
ences of protein to energy ratio in breakfast on mood,
alertness and attention in healthy human volunteers. The
aim of the present study was to examine the effects of
HP breakfast on mood, alertness and attention of under-
graduate student. It was hypothesised that (1) some det-
rimental mood would be alleviated by HP breakfast; and
(2) postprandial alertness and attention be enhanced by
HP breakfast.
2.1. Subjects
Thirteen healthy male volunteer subjects, mean age
21.5 (S.D. 2.8), were recruited from a cohort of present
university students. The study was approved by the
ethical committee of the Guangzhou University of Tradi-
tional Chinese Medicine. All subjects gave their in-
formed consent, both verbally and in writing, after being
informed about the study. All subjects filled out a ques-
tionnaire on lifestyle, medical history, and dietary habits.
They were nonsmokers, no color blind, and had a mod-
erate body mass index (BMI) of 21.3 (S.D. 1.1) kg/m2.
Exclusion criteria for participation were chronic and
current illness; a history of psychiatric or medical illness;
medication use; metabolic, hormonal, or intestinal dis-
eases; irregular diets or deviant eating habits; excessive
use of alcohol, cigarettes, coffee, or drugs; allergy to
milk products; All subjects who participated in the ex-
periment had a BMI in the normal range of Asian adults
(BMI: 18.5 kg/m2 - 22.9 kg/m2), were nonsmokers, and
were not allowed to drink alcohol or take any drug for 2
d before and during the experiment.
2.2. Stud y Design
A repeated-measures, counterbalanced cross-over de-
sign was used. Each subject was tested in two sessions
separated by exactly 1 week. Subjects were told that
various physiological and psychological effects of food
intake were examined, but they were not aware of in-
gesting different ratios of macronutrients. To avoid in-
terferences of learning with treatment effects, the sub-
jects had to practice all questionnaires and tests on two
separate days in the week before the experimental period.
In this way, the subjects were familiar with the experi-
mental procedure.
To ensure similar baseline conditions, subjects were
not allowed to ingest alcohol or caffeine-containing
drinks and foods, and were requested to refrain from
violent physical activity the day before each testing. In
addition, all subjects consumed an identical supper meal
between 1800 and 1900 h on the evening before each
testing. The meal consisted of steamed rice (raw rice 150
g), steamed fish (100 g), almond beancurd (80 g), vege-
tables and fruits (250 g). It provided approximately 3400
kJ, with 65%, 15% and 25% of the energy derived from
carbohydrates, protein and fat, respectively, and the
composition of the meal suggested a medium glycemic
index (GI). In order to avoid a depletion of liver glyco-
gen stores over night the supper was rich in carbohy-
drates and scheduled late. Subjects were asked to ingest
all supper and to have no further food or drinks except
water before testing. Subjects were also asked to sleep
for at least 8 h. Subjects arrived at the institute by public
transport. All subjects were tested simultaneously, be-
ginning at 0700. Just after arrival, subjects had to fill out
a questionnaire checking their compliance with the re-
strictions on the day before as well as their sleep quality
and their actual mental and subjective physical per-
formance. Before the test meal, baseline assessments
were taken in the order (1) questionnaire, (2) alertness
and attention, (3) mood, (4) satiety, (5) body temperature,
(6) blood samplings. Twenty minutes were scheduled for
each of these assessments. Subsequently, the cream-like
test meal was served in a dessert bowl. Subjects spent 10
min to eat whole meal with a spoon and afterwards 5
min to fill in a questionnaire concerning the meal’s ac-
ceptance and sensory properties. For repeated postpran-
dial measurements within the next 4 h, subjects rotated
each hour through the same stations as at baseline. Sub-
jects had free access to pure water during the whole
study, but no additional food or beverages intake was
permitted. Preparation and intake of test breakfast were
Y. C. Zeng et al. / Health 3 (2011) 383-393
Copyright © 2011 SciRes. http://www.scirp.org/journal/HEALTH/
controlled by a dietitian. Subjects were sedentary, and
only reading was allowed in a study room. (Figure 1)
Openly accessible at
2.3. Test Breakfast
The two breakfasts consisted of isoenergetic (3400 kJ),
differed in content of the carbohydrates and protein.
Suspensions mixed at three different ratios: the HP meal
with a PRO/CHO/FAT ratio of 5:3:2; the AP breakfast
with a PRO/CHO/FAT ratio of 1:7:2. All test meals was
controlled by a dietitian and had similar volume and
sensory properties (taste, consistency and color). They
were freshly prepared by mixing appropriate quantities
of basic ingredients and water to obtain 500 ml. Differ-
ent kinds of protein (milk protein and egg white powder)
and carbohydrates (glucose, maltodextrin, rice starch)
were combined to cover a broad range of the representa-
tive compounds that might affect cognitive behavior
differentially. The carbohydrate proportion of the test
meals suggested a medium GI. A differentiation was
only made in the content of carbohydrates and protein,
respectively (Ta b l e 1 ). The meals were served in a ran-
dom order one week apart. Each meal was ingested
within 10 minutes. The energy content of the test meals
was in the range of the subjects’ habitual energy intake
in the morning. Acceptance and sensory homogeneity of
the two meals were tested by staff members of clinical
nutrition department.
2.4. Study Protocol
The study was a 2-day, randomised, crossover trial. At
day 01, subjects were randomly assigned to receive a
breakfast with a high or low ratio of simple-to-complex
carbohydrates. At day 08, after at least 1-week wash-out
period, subjects received the alternate breakfast. The
subjects were instructed to eat and drink the same foods
the evening before a test day. After they subjects arrived
at the institute, they filled out a wellbeing questionnaire,
and were weighed. Their subjects blood glucose and
insulin concentrations were examined after an 8 hour
fast. When the subjects rested 10 min, their body tem-
perature were measured. Then, the subjects started eating
the test breakfast immediately. After breakfast, which
was consumed in 10 min, the subjects were not allowed
to eat or drink anything during 4 h. Blood was collected
at 0, 60, 120, 180, 240 min after breakfast. Immediately
after each blood sample was taken, the subjects filled out
Visual Analogue Scales (VAS) to measure their subjec-
tive feelings of hunger, fullness. Simultaneously, body
temperature was recorded .The subjects received tests
about mood, alertness and attention at fasting, 120, 240
min after breakfast.
arrival and
alertness and attentionmoo
lood sam
test breakfast and questionnaire
Figure 1. Schedule of experimental procedures for the subjects on each test morning. The first and second pe-
riod followed the same order of procedures.
Y. C. Zeng et al. / Health 3 (20 11) 383-393
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Table 1. Composition of the cream-like test meals (3400 kJ; 50 ml).
Basic ingredients
PRO/CHO/FAT [5:3:2]
PRO/CHO/FAT [1:7:2]
Glucoseb 6.1 14.9
Maltodextrinc 52 119.7
Rice starchd 6.1 14.9
Milk proteine 95.4 18.9
Dried chicken 10.6 2.1
Egg white
Soybean oilg 15 15
Water 350 300
aFor sensory acceptance, 0.5 g/L of a nonenergetic powdered mixture of sweeteners (aspartame:acesulfame-K = 1:1) as well as 3
ml/L of vanilla flavor (Beijing first delicious Food Co., LtdSwitzerland) were also added before mixing. The creams were later col-
ored, using an egg-yellow food color (1 ml/L, Shanghai Dyestuffs Research Institute Co., Ltd. China), to get an identical appetizing
yellow color. bGlucose, commercially available from Tanye (Tianjin) Food Co., Ltd. China. cMaltodextrin (Tanye). dRice strarch
(Tanye). eMilk protein, commercially available from Shanghai Insight Protein Nutrition Institute, China. fegg white powder, com-
mercially available from Shanghai Insight Protein Nutrition Institute, China. gSoybean oil, commercially available from COFCO,
2.5. Blood Glucose and Insulin
Blood was collected by finger prick with a DR- II
Automatic Blood Sampler lancet device (Eicom, Japan).
Plasma glucose was measured by using a blood glucose
meter (OneTouch Ultra, LifeScan Inc.). Serum was
pooled for each subject, and plasma insulin was meas-
ured by radioimmunoassay using commercial kits (Bei-
jing North Institute of Biological Technology, China).
2.6. Body Temperature Measurement
Subjects were instructed to remain awake and not to
move, fidget or talk once test breakfast was finished
eating. Body temperature was measured by means of a
rectal thermistor (Zhangzhou Shuangjia Medical Equip-
ment Co., Ltd, China), except during showers and bowel
movements, and room temperature was maintained at 24
- 25 as measured with an air conditioner.
2.7. Satiety
A validated satiety score numerical scale was used
according to the method of Haber et al [23] on the basis
of a scoring system with grades from 10 cm (extreme
hunger) to 10 cm (extreme satiety) VAS. VAS are often
used to measure subjective appetite sensations and the
validity and reproducibility have been shown in several
studies [23,24]. Subjects were instructed to rate them-
selves by marking the scale at the point that was most
appropriate to their feeling at that time. The distance
from this point to the left end of the scale was measured
in mm; changes from baseline were calculated by sub-
tracting the baseline score (5 min) from the score at a
certain time point.
2.8. Mood and Alertness State
The VGZ [25] is a self-administered questionnaire
assessing how participants “feel at the moment.” Sub-
jects were asked to rate 15 items in relation to their
mood. The items were clustered into the 5 dimensions of
negative affect (depressed, unhappy, and queasy), posi-
tive affect (happy, well, and cheerful), information up-
take (fascinated, interested, and uninterested), arousal
(calm, nervous and agitated), and alertness (tired, sleepy
and awake). All answers were given on a 5-point rating
scale ranging from not at all to very much.
2.9. Continuous Performance Test
The continuous performance test (or continuous atten-
tion test) presents stimuli-target and non-target in a mix-
ture at regular intervals. The CPT is a tool to test task
vigilance and distractibility by allowing the subject to
react in the presence of a prescribed specific target. Vis-
ual stimuli consisted of individual letters and were pre-
sented sequentially on a computer screen for 250 ms
each. Subjects were instructed to press a button when-
ever the letter A (correct cue) was followed by the letter
X (correct target). All other sequences were to be ig-
nored, including sequences in which an incorrect cue
(designated ‘B’, but comprising all letters other than A or
X) was followed by the target letter (X) or sequences in
which a correct cue (A) was followed by an incorrect
target (designated ‘Y’, but comprising all letters other
than A or X). Stimuli were presented in four blocks of
280 stimuli (140 pairs) each. Within each block, 50% of
Y. C. Zeng et al. / Health 3 (20 11) 383-393
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the cue-target sequences were presented with short (0.8 s)
interstimulus interval (ISI) and 50% with long ISI (4 s).
Short and long ISIs were pseudorandomly intermixed.
The time between stimulus pairs was constant at 0.8 s.
Of the stimulus pairs, 70% were AX sequences; all other
sequences (BX, AY, BY) occurred with a probability of
0.1 each. The results were converted into values of as-
sessments on the basis of standard computation from the
normal group of the same age [26]. The measured values
were used for statistical analyses.
2.10. Statistics
All statistical analyses were performed with SPSS
version 15.0 for Windows (SPSS Inc., Chicago, IL,
USA). Results were expressed as mean ± standard de-
viation (s.d.), unless stated otherwise. The obtained data
(blood parameters and questionnaires) were analysed by
means of t-tests to investigate the differences between
the two sorts of breakfast. A repeated-measures analysis
of variance was carried out to determine possible differ-
ences between conditions. Linear correlation analyses
were performed to determine the relations between body
temperature and selected variables. Effects of HP were
evaluated using repeated-measures ANOVAs with ses-
sions (HP vs AP) and time (baseline vs HP/AP admini-
stration) as repeated measures. For the analyses of per-
formance of CPT, dependent measures consisted of hit
rate (correct detection of AX sequences) and false alarm
rates to BX, AY, or BY sequences. Effects of HP break-
fast on hit rate were evaluated with 2 × 3 × 2 factorial
repeated-measures ANOVAs with session (HP vs AP),
time (baseline vs HP/AP administration), and ISI (short
vs long) as repeated measures. For analyses of false
alarm rates, an additional within-subject factor with
three levels denoting false alarm type (BX vs AY vs BY)
was included. Differences between rates of BX errors
and AY and BY errors, respectively, during the two
phases of both sessions were evaluated with simple
within-subject contrasts involving session (contrast: HP
vs AP), time (contrast: Baseline vs HP/AP administra-
tion), and false alarm type (contrast: BX vs AY; BX vs
BY). Post hoc paired t-tests were used to assess specific
differences if indicated. Significance was defined as P <
3.1. Glucose and Insulin
Postprandial plasma glucose and insulin concentra-
tions after the HP were increased less than after the AP
within 60 minutes. However, plasma glucose and insulin
concentrations after the HP meal were decreased less
than after the AP 60 minutes, with significant differences
between the HP and AP, with significant differences be-
tween the HP and AP meals. There were also significant
Meal × Time interactions (F = 1745.32, P = 0.000 for
glucose; F = 886.80, P = 0.000 for insulin) (Figure 2).
3.2. Body Temperature
Body temperature rose steadily all experiment session
on both diets. The change in body temperature from the
fasting baseline value was +0.1, +0.1, +0.2, +0.4
at 0 min, 60 mim, 120 min, 180 min and 240 min
after the AP breakfast meal respectively; after the HP
breakfast meal, the change in body temperature from the
Time (min)
AP 400
< 0.01
240 180 120
Time (min)
Figure 2. Profile plots for glucose and insulin responses to HP breakfast and AP breakfast. Mean
(S.E.M.); n = 13.
Y. C. Zeng et al. / Health 3 (20 11) 383-393
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fasting baseline value was +0.1, +0.2, +0.6, +0.8
, +0.7 respectively. Body temperature after HP in-
creased more than AP (t120 min = 2.41, p = 0.024; t180 min =
3.77, p = 0.001; t240 min = 3.88, p = 0.001) There were
also significant Meal × Time interactions (F = 74.56, P =
0.000) (Figure 3).
3.3. Satiety
Ingestion of HP breakfast resulted in a significantly
higher satiety than the AP breakfast, with significant
differences between the HP and AP meals. There were
also significant Meal × Time interactions (F = 106.03, P
= 0.000) (Figure 4).
3.4. Mood and Alertness State
Consumption of breakfast showed positive effects on
the mood of the study population. Intake of HP breakfast
caused improvements in positive affect (time240:t = 5.22,
P = 0.000), information uptake (time120:t = 2.89, P =
0.008; time240:t = 2.67, P = 0.013) and alertness
(time120:t = 2.77, P = 0.011; time240 :t = 3.07, P = 0.005)
and a decrease in negative affect (time120:t = 2.36, P =
0.027; time240:t = 2.91, P = 0.008) and arousal
(time120:t = 2.37, P = 0.026; time240:t = 2.44, P =
0.023). There were also significant Breakfast × Time
interactions (Table 2).
240180 120
Body temper ature
< 0.01
Figure 3. Profile plots for body temperature responses to HP
breakfast and AP breakfast. Mean (S.E.M.); n = 13.
< 0.01
Satiety score
Figure 4. Profile plots for satiety score responses to HP break-
fast and AP breakfast. Mean (S.E.M.); n = 13.
Table 2. Effect of breakfast on mood (VGZ) and results of multifactorial analysis of variance with repeated measures.
Score, Mean ± SD Breakfast Time Breakfast* Time
Negative affect, t Before
Negative affect, t120
Negative affect, t240
Positive affect, t Before
Positive affect, t120
Positive affect, t240
Informationuptake, tBefore
Information uptake,t120
Information uptake, t240
Arousal, t Before
Arousal, t120
Arousal, t240
Alertness, t Before
Alertness, t120
Alertness, t240
3.60 ± 0.54
3.31 ± 0.51*
3.25 ± 0.52*
5.20 ± 0.67
6.27 ± 0.59
6.97 ± 0.72*
4.57 ± 0.39
5.29 ± 0.37*
5.40 ± 0.48*
2.84 ± 0.15
2.39 ± 0.29*
2.41 ± 0.36*
4.14 ± 0.52
4.91 ± 0.47*
5.03 ± 0.57*
3.91 ± 0.37
3.73 ± 0.37
3.77 ± 0.39
5.00 ± 0.63
6.18 ± 0.62
5.66 ± 0.54
4.56 ± 0.35
4.91 ± 0.31
4.92 ± 0.44
2.96 ± 0.29
2.64 ± 0.26
2.71 ± 0.27
4.08 ± 0.53
4.41 ± 0.45
4.36 ± 0.54
*Significantly different from AP, P < 0.05 (mixed-model ANOVA).
Y. C. Zeng et al. / Health 3 (20 11) 383-393
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3.5. Continuous Performance Task
HP breakfast was associated with a significant raise
the hit rate at both ISIs. Post hoc t-tests confirmed sig-
nificantly higher hit rates during HP breakfast than dur-
ing the baseline and AP session. HP breakfast was asso-
ciated with a decline of false alarms, which was most
pronounced for false alarms to AY and BX sequences at
long ISIs. HP breakfast also declined for false alarms to
AY and BX sequences at short ISIs. In addition, there
were not false alarms to BY at any moments in two ses-
sions (Figure 5).
4.1. Blood Glucose and Target Variables
Three kinds of positive emotion were correlated with
concentrations of blood glucose at 240 min (r240min =
0.65, p = 0.000). Two kinds of negative emotion were
negative correlation with concentrations of blood glu-
cose (r240min = 0.53, p = 0.006). Total continuous per-
formance task scores at 240 min were correlated with
concentrations of blood glucose (r240 min = 0.87, p =
0.000). No significant associations were observed be-
tween total CPT scores and concentrations of blood glu-
cose at 0 min, 120 min.
4.2. Body Temperature and Target Variables
Three kinds of positive emotion at three moments
were correlated with body temperature significantly (rbe-
fore = 0.86, p = 0.000; r120min = 0.95, p = 0.000; r240min =
0.95, p = 0.000). Two kinds of negative emotion at three
moments were negative correlation with body tempera-
ture (rbefore = 0.78, p = 0.000; r120 min = 0.95, p = 0.000;
r240 min = 0.91, p = 0.000). Furthermore, total continu-
ous performance task scores before breakfast, at 120 min
and 240 min after breakfast all were correlated with
body temperature (rbefore = 0.59, p = 0.002; r120 min = 0.73,
p = 0.000; r240 min = 0.85, p = 0.000).
The present study showed that differences within pro-
tein to energy ratios in an isoenergetic breakfast can re-
sult in a different effect on perception of satiety, mood
state and CPT scores in healthy male subjects. Our data
reveal significant HP breakfast meal effects as well as
Meal × Time interactions for CPT scores after the inges-
tion of meals with different protein to energy ratios in
the morning. Overall CPT performance was better after
HP breakfast meal than after AP breakfast. In addition,
changes in CPT performance and mood were related to
postprandial changes in glucose concentrations and body
temperature. Two test meals were moderately liked by
the subjects. As energy content, volume, acceptance, and
sensory properties of our test meals were matched, the
observed effects on metabolic, mood, and CPT scores
can be attributed to the ratio of protein to energy in-
gested. Interpreting cognitive effects after macronutrient
ingestion, the energy content, sex, age and the constitu-
tion of the subjects as well as the time have to be con-
sidered [27]. Our subjects were healthy young male stu-
dents, and the test meals matched their habitual breakfast
size. The subjects’ glycogen stores were approximately
not completely depleted because of the carbohy-
240 min 120 min
Short ISI Hit Rate
a a
Long ISI Hit Rate
HP 0.08
Short ISI FA Rate
Short ISI FA Rate
a e
Long ISI FA Rate
Long ISI FA Rate
240 min120 min
Before 240 min120 min
Figure 5. Effects of HP breakfast and AP breakfast on CPT performance. Mean (S.E.M.); n = 13. Bars without a
common superscript differ significantly (P < 0.01).
Y. C. Zeng et al. / Health 3 (20 11) 383-393
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meal on the evening before the test day. Because the GI
of the evening meal was approximately medium, it may
not have influenced the glucose tolerance of the subjects
at the following morning significantly. Young healthy
males are less sensitive to nutritional variables than
young females and older people [28] or stress-prone in-
dividuals [29]. So our observed effects might be even
more pronounced in vulnerable or malnourished popula-
tion [30].
The Recommended Daily Allowance for protein is 0.8
g/kg and the typical Chinese consumes 1.16 g/kg or
about 15% of dietary energy as protein [31]. Advocates
of high protein diets often recommend that protein in-
takes meet or exceed 25% of dietary energy. High pro-
tein diets can reduce postprandial glucose rise and
maintain stabilization of postprandial insulin are known
[32,33]. Consistent with the protein content of our test
meals, plasma glucose and insulin concentration changed
less after the HP meals than after the AP meal. These
differences were most pronounced at 0 min, 60 min and
240 min after test meal ingestion. Because the brain is
very sensitive to changes in nutrient supply, small meta-
bolic changes may influence behavior performance [34].
An ‘inverted U’-shaped dose-response curve was re-
ported for the effects of plasma glucose [35], and insulin
concentration [36] on cognitive functions. It is likely that
the ascending or descending part of an ‘inverted U’ rela-
tion represents the acute positive and negative effects of
a rise or fall [37,38] in blood glucose concentration on
specific cognitive functions. However, constant meta-
bolic conditions [39] might optimize overall cognitive
performance [34,27] for a longer time period. The
plasma glucose concentration remained nearly constant
after the HP meal in present study.
In general, the typical thermic effect of protein is 20%
- 35% of energy consumed, this number usually falls
between 5% and 15% for carbohydrate [40]. A main
reason for the difference in the thermic effects of food
may be due to the fact that the body has no storage ca-
pacity for protein and thus it needs to be metabolically
processed immediately. The synthesis of protein and the
high ATP cost of peptide bond as well as the high cost of
urea production and gluconeogenesis are often cited
reasons for the higher thermic effect of protein [41,42].
Furthermore, concomitant with the thermic response to
the test diets was a slight rise in body temperatures. HP
feeding was associated with a greater degree of body
temperature change versus high carbohydrate (HC)
feeding [42] the changes in body temperature were sig-
nificantly different by diet, HP breakfast was associated
with a greater degree of body temperature change versus
AP breakfast, and at 120 min, 180 min, and 240 min this
change was significant, supporting the contention of
Brundin and Wahren [43] that protein ingestion elicits a
pyrogen-like effect.
There is convincing evidence that a higher protein in-
take increases satiety compared to diets of lower protein
content [33,44,45] at least in the short term. We con-
firmed also that the HP breakfast would increase subjec-
tive satiety, but longer experiments would be useful to
test whether these beneficial effects on the regulation of
appetite can be maintained and have a clinical relevance.
However, the mechanisms by which protein may affect
satiety remain elusive. Satiety is a complicated interac-
tion of psychological, behavioral and physiological
mechanisms. One theory was developed by Mellinkoff
[46]. Since amino acid concentrations are correlated with
a reduction in appetite, Mellinkoff believed there to be a
satiety center in the brain. The satiety center is sensitive
to serum amino acid levels and when levels reach a cer-
tain point, hunger would cease. Another possible mecha-
nism is a relationship between satiety and dietary in-
duced thermogenesis. In the investigation by Wester-
terp-Plantenga [10], differences in satiety over a period
of 24 hour were significantly correlated with differences
in 24 hour dietary induced thermogenesis.
In addition, Blom WA et al [33] believed the HP
breakfast reduced the gastric emptying rate and in-
creased satiety, probably through increased secretion of
cholecystokinin and glucagon-like peptide 1. This study
indicated the effects of HP breakfast on the mood of
healthy males. In assessments performed 0 min, 120 min
and 120 min after breakfast, participants of HP session
reported increased positive affect, information uptake
and alertness. At the same time, participants of HP ses-
sion decreased negative affection and arousal. In contrast,
participants of AP session reported contrary results.
Evidence indicates that macronutrient composition may
influence mood by affecting the synthesis of monoamine
neurotransmitters [47]. It has been suggested that car-
bohydrate-rich meals lead to increased fatigue and de-
creased alertness, whereas meals rich in protein increase
alertness and decrease drowsiness [48,28].
The present study indicated HP breakfast can raise the
hit rate at long ISI and decline of false alarms of both
ISIs than AP breakfast and fasting. Considerable effort
has been devoted to studying the relationship between
body temperature and human performance [49-51]. It
has been reported that cognitive function is improved by
increasing body temperature slightly above the normal
temperature of 37 and that cognitive function is re-
duced by decreasing body temperature below normal
[52,53]. Kleitman [54] originally proposed that the speed
of thinking depends on the level of metabolic activity of
the cells of the cerebral cortex, and by the raising of the
latter through an increase in body temperature we indi-
Y. C. Zeng et al. / Health 3 (20 11) 383-393
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
rectly speed up the thought process. Kleitman’s hy-
pothesis is supported by results from studies [55,56] that
higher brain temperatures resulted in faster transmission,
whereas lower brain temperature resulted in slower
transmission. Moreover, when body temperature was
high, alertness was rated higher.
We also hypothesized that protein exerts its mood ef-
fects partly through the elevation of postprandial body
temperature and glucose concentrations. By bivariate
correlation analyses, we found the positive association
between body temperature and subjective positive mood,
CPT scores at all moments(0 min, 120 min and 240 min);
whereas negative association between body temperature
and subjective negative mood. However, the above-
mentioned association between glucose concentrations
and subjective mood, CPT scores only at 240 min after
test breakfast.
To conclude, HP breakfast can effectively stabilize
postprandial serum glucose concentrations and elevate
postprandial temperature of healthy male undergraduate
students. Our present findings demonstrate the relation-
ship between HP breakfast and mood, alertness and at-
tention. This study indicated that HP breakfast may en-
hance human performance probably by increasing the
thermic effect of a food and elevating body temperature.
This randomized trial demonstrated positive short-term
effects of HP breakfast on mood and CPT performance
in undergraduate students. The observed differences ac-
cording to gender and potential mediating effects be-
tween mood and performance deserve further investiga-
We thank Li-Bo Zhou for providing us with the statistical expertise.
We thank Yan-Lin Zhou, Wen-Feng Zhao and Yun-Zhang for their
technical assistance. We are also grateful to the research volunteers and
a number of assistants of our hospital for their experimental assistance
during the study.
Competing interests: The authors declare that they have no com-
peting interests.
Authors’ contributions: YZ designed and carried out the experi-
ment of this manuscript and drafted the manuscript and approved the
final manuscript; SL and GX participated in the design of the study and
revised the manuscript. HS and JW participated the experiment. All
authors read and approved the final manuscript. All authors lacked any
conflict of interest.
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HP: high protein;
AP: adequate protein;
CPT: continuous performance test;
MI: body mass index;
HC: high carbohydrate;
GI: glycemic index;
VAS: visual analogue scales