Influences of fat, energy, and time of day on mood and performance

Consequences of Circadian Disruption in Shift Workers on Chrononutrition and their Psychosocial Well-Being

The workers and employees in various institutions are subjected to different shifts and work schedules. The employees work not only at daytime but also during odd hours at night. The biological clock of an individual is often altered during night shifts. This affects the psychosocial well-being and circadian nutritional intake of the worker. Disturbance in circadian rhythm results in the development of metabolic disorders such as hypertension, dyslipidemia, dysglycemia, and abdominal obesity. In the present review, we discuss the nature of shift work, sleep/wake cycle of an individual, chrononutrition, dietary habits, and meal changes with regard to timing and frequency, related to shift work. We also discuss the relationship between nutritional intake and psychosocial well-being among shift workers. The review may be beneficial for prevention of metabolic disorders and maintaining sound psychological condition in shift workers.

The role of IL-1 in postprandial fatigue

OBJECTIVES

Cytokines such as IL-1 seems to play a role in the pathogenesis of fatigue associated with some chronic diseases and anti-inflammatory treatment has been shown to reduce these symptoms. Ingestion of a calorie rich meal leads to postprandial fatigue, and is associated with increased systemic concentrations of cytokines, which is more pronounced in obese than lean subjects. We investigated whether postprandial fatigue is regulated by IL-1, and therefore reduced by IL-1 antagonism, in lean and obese subjects.

METHODS

In a double-blind, crossover study in 8 lean and 8 obese male subjects, randomized to receive either saline (placebo) or the IL-1 receptor antagonist anakinra, we investigated whether postprandial fatigue was regulated by IL-1. To promote postprandial fatigue, subjects ran 30 min prior to a high-fat, high-carbohydrate meal. Fatigue was determined using the Stanford Sleepiness Scale and blood samples were drawn at baseline and after the intervention.

RESULTS

IL-1 antagonism led to a reduction in postprandial fatigue and this effect was more pronounced in obese than lean individuals.

CONCLUSIONS

We conclude that IL-1 is involved in the regulation of postprandial fatigue under physiologic conditions in lean and obese individuals. It remains to be shown whether this effect translates into clinical relevant effects.

Macronutrient composition of a morning meal and the maintenance of attention throughout the morning

BACKGROUND

At present, the impact of macronutrient composition and nutrient intake on sustained attention in adults is unclear, although some prior work suggests that nutritive interventions that engender slow, steady glucose availability support sustained attention after consumption. A separate line of evidence suggests that nutrient consumption may alter electroencephalographic markers of neurophysiological activity, including neural oscillations in the alpha-band (8-14 Hz), which are known to be richly interconnected with the allocation of attention. It is here investigated whether morning ingestion of foodstuffs with differing macronutrient compositions might differentially impact the allocation of sustained attention throughout the day as indexed by both behavior and the deployment of attention-related alpha-band activity.

METHODS

Twenty-four adult participants were recruited into a three-day study with a cross-over design that employed a previously validated sustained attention task (the Spatial CTET). On each experimental day, subjects consumed one of three breakfasts with differing carbohydrate availabilities (oatmeal, cornflakes, and water) and completed blocks of the Spatial CTET throughout the morning while behavioral performance, subjective metrics of hunger/fullness, and electroencephalographic (EEG) measurements of alpha oscillatory activity were recorded.

RESULTS

Although behavior and electrophysiological metrics changed over the course of the day, no differences in their trajectories were observed as a function of breakfast condition. However, subjective metrics of hunger/fullness revealed that caloric interventions (oatmeal and cornflakes) reduced hunger across the experimental day with respect to the non-caloric, volume-matched control (water). Yet, no differences in hunger/fullness were observed between the oatmeal and cornflakes interventions.

CONCLUSION

Observation of a relationship between macronutrient intervention and sustained attention (if one exists) will require further standardization of empirical investigations to aid in the synthesis and replicability of results. In addition, continued implementation of neurophysiological markers in this domain is encouraged, as they often produce nuanced insight into cognition even in the absence of overt behavioral changes. ClinicalTrials.gov Identifier: NCT03169283.

The biphasic effects of moderate alcohol consumption with a meal on ambiance-induced mood and autonomic nervous system balance: a randomized crossover trial

Background

The pre-drinking mood state has been indicated to be an important factor in the mood effects of alcohol. However, for moderate alcohol consumption there are no controlled studies showing this association. Also, the mood effects of consuming alcohol combined with food are largely unknown. The aim of this study was to investigate the effects of moderate alcohol combined with a meal on ambiance-induced mood states. Furthermore effects on autonomic nervous system activity were measured to explore physiological mechanisms that may be involved in changes of mood state.

Methods

In a crossover design 28 women (age 18–45 y, BMI 18.5–27 kg/m²) were randomly allocated to 4 conditions in which they received 3 glasses of sparkling white wine (30 g alcohol) or alcohol-free sparkling white wine while having dinner in a room with either a pleasant or unpleasant created ambiance. Subjects filled out questionnaires (B-BAES, POMS and postprandial wellness questionnaire) at different times. Skin conductance and heart rate variability were measured continuously.

Results

Moderate alcohol consumption increased happiness scores in the unpleasant, but not in the pleasant ambiance. Alcohol consumption increased happiness and stimulation feelings within 1 hour and increased sedative feelings and sleepiness for 2.5 hour. Skin conductance was increased after alcohol within 1 hour and was related to happiness and stimulation scores. Heart rate variability was decreased after alcohol for 2 hours and was related to mental alertness.

Conclusion

Mood inductions and autonomic nervous system parameters may be useful to evaluate mood changes by nutritional interventions. Moderate alcohol consumption elevates happiness scores in an unpleasant ambiance. However, drinking alcohol during a pleasant mood results in an equally positive mood state.

Trial Registration

Clinicaltrials.gov NCT01426022.

A Review of the Effects of Lunch: On Adults’ Short-term Cognitive Functioning

Because of widespread irregular lunch consumption by both children and adults, information on the effects of lunch on short-term cognitive functioning is relevant to public health. In September 2012, a MEDLINE search was conducted for studies in which the effects of lunch on cognitive performance were examined. Eleven experimental studies published from 1981 to 1996 were found and evaluated; all involved adults. In three studies, the effects of lunch and lunch skipping were compared; the remaining studies involved a determination of the effects of lunch size and lunch composition. Results of studies in which lunch was compared with no lunch indicate that lunch leads to potential impairment of some aspects of cognitive functioning in the early afternoon. Lunch size may influence cognitive functioning, with impairment more likely to occur after a large lunch than a small lunch. Furthermore, in comparison with low-fat lunches, high-fat lunches seem to result in slower but more accurate responses to some cognitive tasks. However, these suggestions must be viewed with caution, as they are based on only a few studies and are not thoroughly supported by high-quality evidence. In addition, results obtained with adults are not applicable to children. Thus, the potential effects of lunch need further examination in children and adults.

Effects of lunch on children's short-term cognitive functioning: a randomized crossover study

BACKGROUND/OBJECTIVES

Considering the large number of children worldwide attending all-day schools, information on the effects of lunch on short-term cognitive performance is of public health relevance. However, only adult studies investigated this issue yet. Therefore, this study examined the impact of skipping lunch vs having lunch on children's cognitive functioning in the early afternoon.

SUBJECTS/METHODS

Participants in this randomized crossover study with two groups were healthy 6th grade students of an all-day school in Gelsenkirchen, Germany. Group 1 skipped lunch on study day 1 and received an ad libitum lunch 1 week later on study day 2. The order for group 2 was vice versa. In the afternoon tonic alertness, visuospatial memory and selective attention were determined using a computerized test battery of the Vienna Test System. For continuous and discrete interval-scaled variables, treatment effect was estimated using the two sample t-test or the Wilcoxon rank-sum test, for discrete ordinal-scaled variables using generalized linear models.

RESULTS

Data on 105 children (48% male; 12.6 ± 0.6 years) were analyzed. Except for tonic alertness there were no significant differences in cognitive functioning between the skipping lunch day and the having lunch day. The higher number of omission errors on the skipping lunch day lost significance when adjusting for multiple testing.

CONCLUSIONS

In the first study on this topic lunch did not have relevant effects on children's cognitive functioning in the early afternoon. Future research needs to be done to figure out potential methodical and physiological explanations.

Breakfast and snacks: associations with cognitive failures, minor injuries, accidents and stress

One strategy for examining effects of nutrients on cognitive function is to initially investigate foods that contain many different nutrients. If effects are demonstrated with these foods then further studies can address the role of specific nutrients. Breakfast foods (e.g., cereals, dairy products and fruit) provide many important nutrients and consumption of breakfast has been shown to be associated with beneficial effects on cognitive function. Isolating effects of specific constituents of breakfast has proved more difficult and it is still unclear what impact breakfast has on real-life performance. The present study provided initial information on associations between breakfast consumption and cognitive failures and accidents. A second aim was to examine associations between consumption of snacks which are often perceived as being unhealthy (chocolate, crisps and biscuits). A sample of over 800 nurses took part in the study. The results showed that frequency of breakfast consumption (varied breakfasts: 62% cereal) was associated with lower stress, fewer cognitive failures, injuries and accidents at work. In contrast, snacking on crisps, chocolate and biscuits was associated with higher stress, more cognitive failures and more injuries outside of work. Further research requires intervention studies to provide a clearer profile of causality and underlying mechanisms.

Dietary protein and protein-rich food in relation to severely depressed mood: A 10 year follow-up of a national cohort

High-protein diets are advocated to facilitate weight loss, and improve cardiovascular risk factors, but data on psychiatric effects are lacking. We analyzed data from 1947 men and 2909 women aged 25-74 years when examined in 1971-1975 as the baseline of the National Health and Nutrition Examination Follow-Up Study. The amounts of macronutrients were obtained from a 24-hour recall, and frequencies of eating protein-rich foods were estimated using a 3-month food frequency questionnaire. Severely depressed mood (SDM) was defined as Center for Epidemiologic Studies Depression Scale score ≥ 22 or taking anti-depression medication after an average of 10.6 years of follow-up. A significant gender difference was observed in the prevalence of SDM and its association with protein intake. The weighted prevalence of SDM was 11.45 (SE = 0.96) % and 17.45(1.05) % respectively among men and women. Among men, the relative risk (RRs) of SDM were 1.00, 0.46 (95% CI = 0.22-0.99) and 0.38 (0.16-0.92) respectively for the lowest, middle and highest third protein intake (p for trend=0.0347). Among women, the RRs were 1.00, 1.93 (1.23-3.08) and 2.47 (1.24-4.90) respectively with lowest, middle and the highest third intakes (p for trend = 0.0023). These estimates were adjusted for cigarette smoking, alcohol consumption, BMI, socioeconomic status at baseline, and the history of cancer, stroke, heart attack and diabetes assessed at follow-up interview. The authors concluded that increased intake of protein demonstrated a protective effect among men but a deleterious effect among women.

Mood and the macro-nutrient composition of breakfast and the mid-day meal

Six hundred and eighty-six individuals were approached at mid-day after they had chosen a meal in a cafeteria. They were asked to rate their mood during the morning and list what they had eaten that morning. Both males and females who had eaten breakfast rather than fasting reported that they had been happier and more relaxed during the morning. The macro-nutrient compositions of breakfast and lunch were calculated and related to mood during the morning. In males, but not females, the consumption of more carbohydrate in the morning was associated with feeling happy rather than sad and relaxed rather than stressed. Further examination demonstrated that in males the amount of fat, protein and total energy consumed was not associated with mood; that is there was a selective relationship between carbohydrate intake and mood. It was not possible to establish whether the nature of breakfast influenced mood or the pre-existing mood influenced the choice of breakfast although both explanations are plausible. In females, however, there was no relationship between carbohydrate intake and mood, possibly a reflection of the smaller amounts consumed. The suggestion that mood during the morning might influence food choice at mid-day was considered but no association was found.

The Nutritional Status and Eating Habits of Shift Workers: A Chronobiological Approach

The eating habits of workers may vary according to the season of the year and corresponding work schedule. A study aiming at verifying the changes in their diet in summer and winter, as well as the nutritional status of those who work fixed shifts, was conducted. The distribution during the 24h in the quantity of calories and macronutrients ingested and the circadian rhythm of calories consumed were also analyzed. The study was conducted on 28 workers subject to three fixed work (morning, afternoon, and night) shifts at a transport company in the city of São Paulo, Brazil. The mean age of the workers was 32.8 (SD+/-5.3) yrs. Their food intake was ascertained by the use of a 3-day dietary record, and their nutritional status was evaluated by their body mass index (BMI), both in winter and summer. Two-way ANOVA (shift and season) showed food consumption--measured in calories/24 h--was significantly higher in winter than summer (F(1.25)=11.7; p<0.001). No statistically significant differences were found among shifts (F(2.25)=0.85; p<0.44), and the interaction effect between shift and season was also not significant (F(2.25) = 0.15; p < 0.86). No seasonal difference in BMI was detected (Kruskal-Wallis test). Cosinor analyses showed circadian rhythmicity in calories consumed by morning (p < 0.01) as well as afternoon shift workers (p < 0.001), both in the winter and summer. Circadian rhythmicity in calories consumed by night workers was found only in summer (p < 0.01). The changes observed in the workers' eating habits from one season to another and during the 24h period show the need for further studies to help develop educational programs to improve the nutrition of shift employees taking into consideration shift schedule and season of the year when work is performed.

Acute effects of macronutrient manipulations on cognitive test performance in healthy young adults: A systematic research review

The potential for foods to exert effects on behaviour is increasingly recognised. Previous studies have incorporated both well-known and lesser-known cognitive tests in the evaluation of relationships between macronutrient interventions and mental performance. Systematic review methodology was used to identify studies of macronutrient effects on cognition, limited to acute effects in young, fasted, healthy adults. Thirty-one studies met the inclusion criteria, yielding a total of 134 outcome measures. The studies reviewed displayed a predominance of soluble glucose manipulations, and a paucity of complex carbohydrate, protein or fat manipulations. Memory performance was most commonly measured, but verbal fluency, attention, reaction time, psychomotor skill and problem solving were also assessed. Significant differences in performance tended to occur under circumstances of more intense cognitive demand and after delays. Memory emerged as the most sensitive cognitive modality to macronutrient manipulations. Tasks identified as sensitive included Serial Sevens, Free Word Recall and Cued Word Recall, with tentative support for the Word Recognition Task. Findings also suggested that visuo-spatial memory may be influenced by macronutrient manipulations.

Low- and high-carbohydrate weight-loss diets have similar effects on mood but not cognitive performance

BACKGROUND

Low-carbohydrate diets are often used to promote weight loss, but their effects on psychological function are largely unknown.

OBJECTIVE

We compared the effects of a low-carbohydrate, high-fat (LCHF) diet with a conventional high-carbohydrate, low-fat (HCLF) diet on mood and cognitive function.

DESIGN

Ninety-three overweight or obese participants [x +/- SEM age: 50.2 +/- 0.8 y; body mass index (in kg/m2): 33.6 +/- 0.4] were randomly assigned to an energy-restricted ( approximately 6-7 MJ, 30% deficit), planned isocaloric LCHF diet or an HCLF diet for 8 wk. Body weight and psychological well-being were measured by using the Profile of Mood States, Beck Depression Inventory, and Spielberger State Anxiety Inventory instruments at baseline and fortnightly. Cognitive functioning (working memory and speed of processing) was assessed at baseline and week 8.

RESULTS

The LCHF diet resulted in significantly greater weight loss than did the HCLF diet (7.8 +/- 0.4 and 6.4 +/- 0.4 kg, respectively; P = 0.04). Both groups showed improvements in psychological well-being (P < 0.01 for time), with the greatest effect occurring during the first 2 wk, but there was no significant difference between groups. There were no significant between-group differences in working memory (P = 0.68), but there was a significant time x diet interaction for speed of processing (P = 0.04), so that this measure improved less in the LCHF than in the HCLF diet group.

CONCLUSIONS

Both dietary patterns significantly reduced body weight and were associated with improvements in mood. There was some evidence for a smaller improvement in cognitive functioning with the LCHF diet with respect to speed of processing, but further studies are required to determine the replicability of this finding.

The effects of sucrose and maize oil on subsequent food intake and mood

The effects of sucrose and oil preloads were explicitly compared in a single-blind controlled trial using a between-subjects design. Eighty adult subjects (forty-three male, thirty-seven female) aged 18–50 years received at 11.00 hours one of four yoghurt preloads. All were 80 g low-fat, unsweetened yoghurt (188 kJ), containing additionally (1) saccharin (control, 23 kJ), or (2) 40 g sucrose (859 kJ), (3) 40 g maize oil (1569 kJ), (4) 20 g sucrose, 20 g maize oil (1213 kJ). Subjects were normal eaters and of normal weight (male mean weight: 68·8 (sd 3·2) kg, BMI 21·8 (sd 1·6) kg/m2; female mean weight: 53·7 (sd 5·1) kg, BMI 20·4 (sd 1·2) kg/m2). Food intake was measured with a food diary and mood with ten single Likert scales. ANOVA was conducted using preload type (saccharin, sucrose, oil, sucrose + oil), sex (male, female) and early v. late breakfast times as factors. Mood was analysed using the same design, with time of rating (immediate, 60 min, 120 min) as an additional factor. Men ate more after the saccharin preload than after the other preloads, but did not vary the time of their next solid food. Women increased the intermeal interval only after the oil preload, which also had the highest energy content value, but did not vary the energy content of their next solid food. The saccharin preload decreased rated tiredness at 2 h compared with the sucrose preload, possibly due to its lower energy content. The preloads containing sucrose or sucrose + oil increased calmness between 1 and 2 h afterwards, compared with the saccharin preload. It is concluded that both sucrose and oil increase the intermeal interval in men, but that women are less sensitive to preloading. The mood effects suggest that tiredness after carbohydrate at 2 h may in part be a decrease in rated energy compared with the increased rated energy found after a preload with low energy content. Carbohydrate may genuinely increase calmness. These effects apply to non-restrained eaters of normal weight.

Relationship between antral distension and postprandial symptoms in functional dyspepsia

AIM: To investigate in patients with functional dyspepsia (FD) after an every-day meal whether (1) gastrointestinal (GI) and extra-GI symptoms had any relation with the degree of antral volume, (2) the onset of postprandial symptoms was associated with, and may predict, delayed gastric emptying.

METHODS: In 94 symptomatic FD patients, antral volume variations and gastric emptying were assessed with ultrasonography after a 1050 kcal meal. Symptoms were evaluated with a standardized questionnaire. The association of GI and extra-GI symptoms with antral volumes and gastric emptying were estimated with logistic regression analysis.

RESULTS: Forty percent of patients did not report any symptoms after a meal. Compared to the healthy controls, the antrum was more distended in patients throughout the entire observation period and 37 (39.4%) patients had delayed gastric emptying. Only postprandial drowsiness was associated with antral volume variations (AOR = 1.42; P < 0.001) and with delayed gastric emptying (AOR = 3.59; P < 0.03).

CONCLUSION: In FD patients, GI symptoms are neither associated with antral distension nor with gastric emptying. Drowsiness is associated with antral distension and delayed gastric emptying. The onset of drowsiness is preceded by an increment of antral distension and the duration of the symptom appears to be related to the persistence of antral distension.

Effects of a carbohydrate-restricted diet on affective responses to acute exercise among physically active participants

Currently, the carbohydrate-restricted diet is very popular. Atkins' book, Dr. Atkins' Diet Revolution, has sold millions in its more than 25 years of existence. His book promotes the carbohydrate-restricted diet, which focuses on the consumption of proteins and fats as primary calorie and energy sources, while severely restricting carbohydrates. However, when carbohydrates are restricted from the diet, the body's primary energy source is reduced considerably. Therefore, the purpose of this study was to compare the psychological responses to exercise of individuals when on a carbohydrate restrictive diet and when on a noncarbohydrate restrictive diet. For this study, 17 participants practiced a noncarbohydrate-restricted diet for three weeks and the carbohydrate-restricted diet for three weeks, while maintaining previous exercise habits. After each exercise session, the participants completed the Physical Activity Affect Scale, which measures Positive Affect, Negative Affect, Tranquility, and Fatigue. Simple one-way analyses of variance indicated significant treatment differences (ps<.05) relative to Negative Affect, Positive Affect, and Fatigue. The results of the study indicate as predicted, that, when a person restricts carbohydrates from the diet, he will experience more fatigue, more negative affect, and less positive affect in response to exercise than those individuals who are not restricting carbohydrates.

Functional foods: psychological and behavioural functions

It is easier to demonstrate the consistent effects of foods on satiety than on cognitive performance. This is understandable since the satiety system incorporates physiological signalling systems that mediate the effects of foods on function. Specific manipulations of proteins, carbohydrates and fats have the potential to act as functional foods for appetite control. Because of the importance of the optimal functioning of cognitions for survival, these functions are quite strongly protected against short-term dietary and physiological perturbances. Therefore, food manipulations may be better detected through the degree of effort exerted to maintain performance rather than via changes in the actual performance itself. This procedure has not been widely used hitherto. The concept of biomarkers may have to be interpreted differently from research on physiological systems or clinical endpoints. For satiety, adjustments in the profile of hunger could serve as a biomarker or surrogate endpoint. For cognitions, correlated physiological variables may be more difficult to measure than the functional endpoint itself. Changes related to unitary functions (such as tracking) could serve as biomarkers for more complex, integrated skills (such as car driving). Since food manipulations may affect multiple functions, the challenge is to design foods with good satiety control that do not impair mental performance; or alternatively to engineer foods that optimise cognitive performance without compromising satiety. This rapidly developing field has great potential for close collaboration between academia and industry in the production of commercially successful products that show clear improvements in human functioning with the capacity to protect against disease or impairment.

Improving mental health through nutrition: the future

Tell me what you eat, and I will tell you what you are (Anthelme Brillat-Savarin). When I behold a fashionable table set out in all its magnificence, I fancy that I see gouts and dropsies, fever and lethargies, with other innumerable distempers, lying in ambuscade among the dishes. Nature delights in the most plain and simple diet. Every animal, but man, keeps to one dish. Herbs are the food of this species, fish of that, and flesh of a third. Man falls upon everything that comes in his way; not the smallest fruit or excrescence of the earth, scarce a berry or a mushroom can escape him (Joseph Addison). The pleasures of the palate deal with us like the Egyptians thieves, who strangle those whom they embrace (Seneca). Let food be your medicine and medicine be your food (Hippocrates).

The influence of breakfast and a snack on psychological functioning

Although there are reports that breakfast influences both mood and memory, there has been no attempt to consider whether a subsequent snack is beneficial. One hundred and fifty young female adults either fasted or consumed breakfasts of either 10 or 50 g of carbohydrate (corn flakes). Half received a further 25 g of carbohydrate in the form of corn flakes after 1 1/2 h (snack). Predictably, those who ate breakfast, and/or a snack, reported feeling less hungry. The larger the caloric intake, the less subjects reported hunger. Those who consumed a snack reported a better mood. Eating a larger breakfast was associated with poorer mood later in the morning, an effect reversed by eating a snack. Memory for the word lists was not influenced by eating breakfast, however, 20 but not 60 min after a midmorning snack, more words were recalled. Those who had eaten breakfast, as opposed to fasting, did, however, spend longer trying to recall the words. This finding was interpreted as evidence that eating breakfast was associated with better motivation. On a number of occasions, better memory was associated with lower blood glucose levels. These findings support previous observations that better glucose tolerance was associated with better memory.

Macronutrients and mental performance

There is currently intense interest in the effects of macronutrients on psychological states, mental performance, and well-being. A strong theoretical perspective has guided work on carbohydrates and their relation to brain serotoninergic function with concomitant effects on performance. The clearest and most reliable effects have been observed for the beneficial action of glucose on cognitive performance, supported by investigations of hypoglycemia, which is associated with general impairment of cognitive performance. The effects of complex carbohydrates are less distinct and change with time of day; e.g., carbohydrate at breakfast tends to improve morning performance. However, these studies are rarely decisive. Far fewer experiments have been performed on protein and fat, and it is difficult to draw any firm conclusions. Macronutrients are seldom given alone, proportions of protein and fat differ greatly between studies, and comparisons are frequently performed with no food at all. Food intake may mitigate the effects of low doses but not of high doses of alcohol on performance. Effects of macronutrients on cognitive performance may be dependent on their effects on glucose metabolism, metabolic activation, or serotonin. Other factors that modify effects include time of day, circadian rhythms, type of task, habitual diet, and vulnerability of the population.

An examination of the effects of isoenergetic intragastric infusions of pure macronutrients on cold pain perception in healthy human volunteers

Our previous study demonstrated that meals, particularly when rich in fat, significantly reduced the pain induced by the cold pressor stimulus in healthy human subjects. To determine the mechanisms involved, the aim of this study was to bypass the taste and cognitive component of food and to investigate the scope of these analgesic effects with direct intragastric infusion of pure macronutrients in a group of 16 healthy human volunteers (eight male and eight female) on the response to cold-induced pain. All subjects underwent the cold pressor test (CPT) on three occasions in a counterbalanced order: before and after intragastric intubation and infusion of isoenergetic fat (10% intralipid), carbohydrate (CHO-maltodextrin), and a control infusion of isotonic saline. All solutions were of equal volume and administered at room temperature. The CPT was carried out four times on each test day, once before intubation, and 0.5, 1.5, and 2.5 h after intragastric infusion. Radial pulse and blood pressure measurements and visual analogue scales of mood/emotional state were carried out before and after each CPT. There were no significant differences in pain scores between the three test conditions, suggesting that by bypassing the cognitive and taste component of eating, the trigger for any postingestive analgesic effects of food are lost.

Functional food science and behaviour and psychological functions

The impact of ingesting various foods on psychological and behavioural functions is a topic of both interest and concern to the general public. In this article, the scientific literature concerning demonstrated cause-and-effect relationships is reviewed, beginning with methodological considerations specific to the quantification of particular behaviours and psychological events. The essential function of food is to satisfy hunger and the need for essential nutrients. The contributions of macronutrients to appetite and satiety are described, as well as their impact on metabolism and energy balance. Functional properties of macronutrient substitutes (high-intensity sweeteners, fat replacers) and flavour enhancers are examined in relation to their contribution to hunger, satiety, and energy balance. The effects of foods and individual nutrients on the performance of diverse psychomotor tasks are studied with consideration given to the various validated quantitative tools used to assess behaviour. The effects of food components on activation, sedation, and affective states such as dysphoria are also reviewed, with special attention given to brain function and neuroactive substances such as serotonin and the endorphins. The case of hyperactivity in children is given special emphasis with reference to the potential influence of sugar and food additives. Safety issues related to food constituents and additives are discussed. Finally, a set of criteria is proposed for the evaluation and elaboration of studies in the behavioural and psychological fields, along with suggestions for future research.

Effects of carbohydrate and lipid on resting energy expenditure, heart rate, sleepiness, and mood

The effects of gastric infusions of fat and carbohydrate on physiological and psychological measures were compared using a within subject design in 9 healthy subjects (6 males). Each subject received isovolaemic rapid gastric infusions of sucrose solution (100% energy carbohydrate), lipid emulsion (100% energy fat, 20% Intralipid), and a non-nutrient control (0.9% saline) in a randomised order. Nutrient infusions were isoenergetic, containing one-third of an individual subject's estimated daily energy requirements (mean, 3227 kJ; range, 2479-3971 kJ). Measures of heart rate (HR), energy expenditure (EE), mood, and sleepiness were collected before the infusions and every 0.5 h for 3.5 h. Mean postingestive HR, EE, and satiation were significantly greater after the nutrient infusions than after the control. Sucrose induced a rapid increase in HR and EE, whereas lipid had a lesser and more delayed effect. Thirty minutes after the gastric infusions, HR and EE were significantly higher after the sucrose than after the lipid and saline. Hedonic tone was greater and tension lower after the saline and sucrose infusions than after the lipid infusion. From 3 to 3.5 h after ingestion, subjects felt significantly more sleepy after the lipid infusion than they did at these times after the saline infusion, and significantly more dreamy after the lipid infusion than they did after the sucrose infusion. In conclusion, the presence of lipid and sucrose in the intestine induces significant and differing physiological and psychological effects, which are independent of cognitive and orosensory influences.

Effects of meals on objective and subjective measures of daytime sleepiness

Effects of recent food ingestion on daytime sleepiness were assessed in 16 subjects (8 men and 8 women) who were each studied on two occasions, 28 days apart. On each occasion, subjects ate a high-fat low-carbohydrate (CHO) (fat/CHO energy ratio 54:41) meal and an isoenergetic low-fat high-CHO meal (fat/CHO energy ratio 7:88) 4 h apart in a counterbalanced order. Sleepiness was measured at 2-hr intervals by using the Multiple Sleep Latency Test and the Akerstedt electroencephalograph sleepiness test. To control for circadian factors, one group (4 men, 4 women) ate the meals 2 h later than did the other group of subjects. There were no differences in sleepiness according to the composition of the meal. Sleepiness in the Multiple Sleep Latency Test was significantly greater 1.5 h after the meals were eaten than before (F 11.37; df 1,15; P = 0.004). Sleepiness was also enhanced in the Akerstedt sleepiness test 3 h 20 min after the meals. The results suggest that the meals induced an enhancement in sleepiness that was not solely due to circadian rhythms.

Alterations in mood after changing to a low-fat diet

The effects on mood of reducing dietary fat while keeping the energy constant were examined in ten male and ten female healthy volunteers aged between 20 and 37 years. Each volunteer consumed a diet containing 41% energy as fat for 1 month. For the second month half of the subjects changed to a low-fat diet (25% energy from fat) and the remainder continued to eat the diet containing 41% energy from fat. Changes in mood and blood lipid concentrations were assessed before, during and at the end of the study. Profile of mood states (POMS) ratings of anger-hostility significantly increased in the intervention group after 1 month on the low-fat diet, while during the same period there was a slight decline in anger-hostility in the control subjects (group F 6.72; df 1.14; P = 0.021). Tension-anxiety ratings declined in the control group consuming the higher fat diet but did not change in the group consuming the low-fat diet (group F 6.34; df 1.14; P = 0.025). There was a decline in fasting concentrations of HDL-cholesterol after the low-fat diet and a small increase in subjects consuming the medium-fat diet (group F 4.96; df 1.12; P = 0.046), but no significant changes in concentrations of total serum cholesterol, LDL-cholesterol or triacylglycerol were observed. The results suggest that a change in dietary fat content from 41 to 25% energy may have adverse effects on mood. The alterations in mood appear to be unrelated to changes in fasting plasma cholesterol concentrations.

Effects of a specific CCK-A antagonist, Loxiglumide, on postprandial mood and sleepiness

Previous studies have demonstrated that feelings of sleepiness increase after ingestion of a fat-rich meal. The aim of the study was to test the hypothesis that postprandial sleepiness is mediated by cholecystokinin (CCK) acting on CCK-A receptors. A double-blind crossover study was conducted. Twelve male volunteers ate a high-fat morning meal [54% energy fat, 41% energy carbohydrate (CHO)]. On one day they received an i.v. infusion of Loxiglumide, a CCK-A receptor antagonist (30 mg/kg/h for 10 min then 10 mg/kg/h for 3 h 10 min). On another day the protocol was repeated except a saline placebo infusion was given at similar rates as the Loxiglumide, starting 20 min before the meal. Subjects' mood and sleepiness were monitored throughout using questionnaires and performance tasks. The results indicate that ratings of vigour were significantly lower during the Loxiglumide infusion than during the saline infusion, [F(1,10) = 6.65; p = 0.027]. Subjects who were infused with Loxiglumide on their first test day felt significantly (p < 0.05) more fatigued, sleepy and tense and less vigorous, less efficient and had lower energetic arousal during the Loxiglumide infusion than during the saline infusion. In conclusion, the results suggest that the postprandial decline in feelings of alertness after a fat-rich meal is not mediated solely by CCK acting through CCK-A receptors.

The influence of food on pain perception in healthy human volunteers

The aim of this study was to investigate if food could reduce pain perception in a group of 16 healthy human volunteers (8 male and 8 female), and to explore the differential effects of macronutrient composition on the response to cold-induced pain. All subjects underwent the cold pressor test (CPT) on 3 occasions in a counterbalanced order, before and after administration of isoenergetic high-fat low-carbohydrate (CHO) and high-CHO low-fat meals, and when no meal was given. The CPT was carried out 4 times on each test day, once before the meal, and 0.5, 1.5, and 2.5 h after the meal, and at the equivalent times on the day when no food was given. Radial pulse and blood pressure measurements and visual analogue scales of mood/emotional state were carried out before and after each CPT. Mean pain scores were significantly reduced following both meals compared with the no-food condition. The maximum reduction in pain occurred 1.5 h after ingestion, and a significantly greater effect was exerted by the high-fat low-CHO meal compared with the high-CHO low-fat meal. These results demonstrate that food, particularly when rich in fat, significantly reduces the pain induced by the cold pressor stimulus in healthy human subjects.

Influences of fat and carbohydrate on postprandial sleepiness, mood, and hormones

Paired studies were conducted in 18 healthy volunteers (9 men, 9 women) to investigate whether differences in mood and daytime sleepiness induced by high-fat-low-carbohydrate (CHO) and low-fat-high-CHO morning meals were associated with specific hormonal responses. Plasma insulin concentrations were significantly higher after low-fat-high-CHO meals, and cholecystokinin (CCK) concentrations were significantly higher after high-fat-low-CHO meals. Subjects tended to feel more sleepy and less awake 2-3 h after the high-fat-low-CHO meal, and ratings of fatigue were significantly greater 3 h after the high-fat-low-CHO meal than after the low-fat-high-CHO meal. The results of the present study are consistent with the hypothesis that there is an association between the lassitude experienced after a meal and the release of CCK.