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Neurosciences
A growing body of literature suggests dietary components can support mood and cognitive function through the impact of their bioactive or sensorial properties on neural pathways. Of interest, objective measures of the autonomic nervous system—such as those regulating bodily functions related to heartbeat and sweating—can be used to assess the acute effects of dietary components on mood and cognitive function. Technological advancements in the development of portable and wearable devices have made it possible to collect autonomic responses in real-world settings, creating an opportunity to study how the intake of dietary components impacts mood and cognitive function at an individual level, day-to-day.
- dietary components
- autonomic nervous system
- stress
1. Introduction
In our rapidly changing world, various factors can affect our body and environment, leading to changes in mood and cognitive performance. Upon detecting a factor or a stimulus, the body can enter a state of alertness [1] and its homeostasis can be disrupted, leading to a state of stress [2]. To maintain the body’s homeostasis or prepare the body for action, the autonomic nervous system (ANS) initiates a cascade of physiological signals. These signals guide modifications in behaviour and cognitive function to address the new demands associated with the stimulus [3,4]. Certain dietary components with bioactive mechanisms (e.g., caffeine) or sensorial properties (e.g., peppermint) can act on the neural circuitry involved in mood and cognitive function, potentially helping individuals better react to novel situations and demands [5,6].
Although several nutritional interventions have evaluated the acute effects of dietary components on stress, alertness, and cognitive performance using standardized and/or valid approaches, these traditional methods have limitations that can lead to biased outcomes [7,8,9]. These methods, including subjective assessments and cognitive tasks, require repeated measurements for accuracy and experimental manipulation, potentially leading to habituation and cognitive bias [7,8]. Additionally, subjective assessments can lead to biased outcomes as they must be reported at time points determined before the experiment [8]. Lastly, subjective ratings can introduce subjective bias into the experiment’s results [9].
Recently, the use of ANS responses has emerged as a reliable and objective approach for assessing the acute effects of dietary components on stress, alertness, and cognitive performance [8,9]. By responding to changes in the effort associated with cognitive function as well as changes in arousal and valence linked to mood, ANS responses have the potential to provide reliable measures for evaluating the effects of dietary components [10,11]. The sympathetic nervous system (SNS), one of the two sub-branches of the ANS, is typically associated with a state of arousal that underlies high levels of stress or alertness [12]. On the other hand, the activation of the parasympathetic nervous system (PNS), the other sub-branch of the ANS, is linked to physical well-being and a state of positive valence, which can underly a low level of stress [13]. Additionally, the prefrontal cortex may indirectly regulate ANS activity to maintain the effort required for cognitive function to meet the demands of everyday living [14]. Hence, the SNS is activated during cognitive effort, while the PNS may help regulate this effort and facilitate recovery. The SNS mediates physiological changes such as pupil dilation, increased heart rate (HR), peripheral vasoconstriction, and enhanced sweat gland secretion. PNS activation leads to antagonist responses, particularly a decrease in HR, resulting in enhanced heart rate variability (HRV) [10,11].
Several intervention studies have attempted to demonstrate the acute effect of dietary components on stress, alertness, and cognitive performance by recording ANS responses in complement to cognitive tasks and subjective ratings that are standardized and/or valid [15,16,17,18,19,20,21,22,23,24,25,26,27,28]. In these studies, ANS responses are typically assessed using laboratory devices such as electrocardiograms (ECGs) to measure HR [29], skin electrodes to track the increase in skin galvanic response (GSR) resulting from sweat gland secretion [30], eye trackers to quantify pupil dilation [31], or thermistors to measure changes in skin temperature [32]. The measurement of ANS responses in conjunction with cognitive tasks and subjective assessments has allowed the demonstration of the acute effects of dietary components on mood states and cognitive function in several studies [19,20,21,22,26,33].
2. Dietary Components to Relieve Stress Acutely
Studies have shown the potential usefulness of ANS responses as a means by which to assess the acute effect of dietary components on stress. Among natural sources of amino acids, Tryptophan and L-theanine have received particular attention due to their ability to modulate stress by targeting neural pathways responsible for regulating mood [5,34]. A recent study by Zahar S, Schneider N, Makwana A, Chapman S, Corthesy J, Amico M and Hudry J [35] suggested that an egg protein hydrolysate food matrix incorporating a dietary source of the amino acid Tryptophan at a 1 g dose can reduce ANS response to acute stress induced by cognitively demanding tasks. This was reflected by an increase in HRV in comparison with a placebo. Similarly, the findings of another study examining the effects of L-theanine intervention (oral administration of a 200 mg dose diluted in water) 20 min post-absorption demonstrated a reduction in autonomic response to stress induced by a mental arithmetic task, as evidenced by lower HR compared with a placebo [36].
Research attempting to mediate stress via dietary intervention has yielded mixed findings from ANS outcome measurements. Despite strong indication that the herbal component “green oat” can reduce stress [39], this was not supported by results from stress-related measurements conducted by Kennedy DO, Bonnlander B, Lang SC, Pischel I, Forster J, Khan J, Jackson PA and Wightman EL [16]. Indeed, the findings of this study did not show a reduction in GSR in an experimental procedure of multiple cognitive tasks with a targeted stress effect. Similarly, the reduction in subjective stress observed by Boyle NB, Billington J, Lawton C, Quadt F and Dye L [38] following the intake of a combination of magnesium (150 mg elemental), green tea (125 mg containing 40% L-Theanine), rhodiola extract (222 mg), and B vitamins (0.7, 0.1, and 0.00125 mg of vitamins 𝐵6, 𝐵9 and 𝐵12, respectively) was not associated with a reduction in autonomic arousal. This disconnection between ANS and subjective measures of stress was also noticed in the Tryptophan intervention conducted by Zahar S, Schneider N, Makwana A, Chapman S, Corthesy J, Amico M and Hudry J [35].
3. Dietary Components That Acutely Enhance Alertness
Evidence shows the potential of ANS responses to mirror changes in alertness following the intake of a dietary component. This is particularly supported by caffeine studies. Caffeine’s well-known effect on alertness is mediated through the antagonism of adenosine receptors which, in turn, leads to a stimulated release of neurotransmitters such as noradrenaline, dopamine, and acetylcholine [40]. Following a typical absorption period of 30 min, caffeine administration has been associated with sympathetic activation together with an increase in subjective alertness and/or a decrease in reaction time to a sustained task (RT) as another measure of alertness [19,20,21,22,26]. Similarly, Redondo B, Vera J, Carreño--Rodríguez C, Molina-Romero R and Jiménez R [19] showed increased pupil dilation and subjective rating of alertness 30 min following the intake of a caffeine beverage (caffeine doses ranged from 200 mg to 340 mg adjusted by the subject’s weight) compared with a placebo. This supports previous observations that heightened sympathetic activity, which can be induced by caffeine, causes a contraction of the iris dilator muscle, leading to pupil dilation [41].
Acute nutritional interventions targeting effects on alertness with ANS responses as outcome measures have also resulted in mixed findings. While the hypothesis that ‘caffeine enhances alertness’ was supported by the increase in GSR, it was also contradicted by the trend towards a decrease in HR and an increase in blood pressure in the study conducted by Quinlan PT, Lane J, Moore KL, Aspen J, Rycroft JA and O’Brien DC [26]. This pattern might reflect a predominance of the baroreflex mechanisms being activated by caffeine [40]. The effects of caffeine can also depend on the composition of the matrix through which it is administered [43]. In the study by Bichler A, Swenson A and Harris M [44], the ingestion of a mix of caffeine and taurine (incorporated in a pill at serving doses of 100 mg and 1000 mg, respectively) was followed by a decrease in HR 45 min after intake. It may be that caffeine induced a baroreflex-mediated response, reflected by a decrease in blood pressure, potentially facilitated by taurine, as an amino acid with a vasoactive property.
4. Dietary Components to Improve Cognitive Performance Acutely
Scientific literature provides evidence supporting the utilization of ANS responses in enhancing our comprehension of the acute impact of dietary components on cognitive performance. The improvement in cognitive performance can be the result of the bioactive or sensorial properties of the dietary component. The ability to maintain cognitive effort could also be favorized by enhanced alertness or stress reduction. Indeed, synergistic effects on mood states and cognitive performance were observed in several caffeine intervention studies [23,24,47]. Evidence of caffeine’s impact on ANS activity suggests an increase in HRV and pupillary dilation after the consumption of the component [48]. Improvement in cognitive performance can also be acutely induced with non-nutritional interventions. By triggering a higher cerebral activity through mastication, chewing gum might enhance the delivery of oxygen and glucose to neural regions involved in cognition, leading to better cognitive performance [49].
Studies investigating the effects of dietary components on cognitive performance using ANS responses as outcome measures have resulted in mixed findings (Table 3). While there appears to be an association between caffeine consumption and cognitive function, several factors may influence this relationship, including the timing of consumption, dosage, experimental conditions, expectancy bias, population demographics, and habitual intake of caffeine [53,54,55]. In the study conducted by Pomportes and colleagues [52], a decrease in parasympathetic modulation was observed following caffeine (100 mg) ingestion. In the same study, the ingestion of a multi-vitamin-mineral preparation supplemented with 300 mg guarana led to a significant improvement in decisional cognitive performance and stability in parasympathetic modulation. Relatedly, the constituents of dietary components can synergistically impact cognitive performance, as demonstrated in the study by Scholey AB and Kennedy DO [45]. Their research found that while neither herbal extract flavoring nor caffeine alone improved cognitive performance, an energy drink containing all these constituents led to better memory and attention performance compared with a placebo.
5. Conclusions
Overall, ANS responses are reliable and valid objective measures that can be used to explore the impact of acute nutritional interventions on mood states and cognitive function. Algorithms for automatic detection of mood and cognitive changes integrated to multi-sensor platforms, wearables, or contactless devices open up new possibilities for personalized nutritional interventions and recommendations [65]. Tailoring nutritional advice, products or services to individual variability, characteristics and needs represents the main goal of the growing field of personalized nutrition [66]. Compared with generalized approaches, personalized nutrition may lead to significant enhancement of health outcomes as well as behavioral changes [67]. This is achieved through the use of external monitoring devices, which inform individuals about their physiological state and effectively facilitate the adoption of healthy behaviors by boosting motivation and precisely targeting desired health outcomes [68]. However, this approach requires richer and more robust data to account for variables inherent to ecological setup and further research is needed to better validate the link between ANS responses, mood states, and cognitive function.
This entry is adapted from the peer-reviewed paper 10.3390/brainsci13081177
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