A preliminary, single-day field study was conducted to assess whether energy intake at breakfast prior to morning exercise influenced cognitive function, mood, appetite and EI for the remainder of the day. An increase in EI at breakfast was associated with lower mental fatigue, higher alertness and EI and better overall mood post-exercise. The limitations of conducting a field study are obvious; a lack of control over the environment in which the study is completed which may lead to confounding results and the inability to detect subtle effects which may only become apparent in a more controlled environment. Participants notoriously under-report when asked to complete a food diary, decreasing the internal validity of the data [ 38 ]. For this reason, collecting additional data on a subsequent day would have been preferable. However, these results did suggest that breakfast size before exercise may influence energy intake and mood in active females, warranting further investigation in a randomised controlled trial as subsequently discussed.

4.2. Main Study

Beneficial pre-exercise nutritional practices for females exercising for weight control or mood and cognitive benefits have not been well established. The main study presented in this paper aimed to assess the effect of breakfast size prior to exercise on post-exercise cognitive performance, mood and appetite in healthy, habitually active females. Breakfast consumption compared to breakfast omission prior to exercise improved subjective hunger ratings, irrespective of size. Breakfast was also favourable for some mood benefits in the hours following exercise, but consuming a smaller breakfast (118 kcals) prevented mid-afternoon cognitive decrements associated with consuming a larger breakfast (236 kcals).

et al. , (2007) also found higher blood glucose accompanied increases in alertness and contentment when breakfast was consumed rather than omitted [ Feelings of relaxation were enhanced in the initial post-exercise period when either breakfast was consumed, a positive finding given that women sight stress reduction as a main reason for exercise [ 9 ]. Consuming breakfast replicated the usual routine of this sample and some evidence suggests that habitual breakfast habits may influence mood responses to acute breakfast consumption [ 39 40 ], which may explain this finding. In addition, past research suggests that CHO intake may reduce the effects of energy depletion in the brain by attenuating the synthesis of certain metabolites and neurotransmitters [ 41 ]. Previously, a higher concentration of plasma glucose was observed immediately post-exercise when CHO, compared to placebo, had been consumed during a moderate intensity 2 h cycle, which corresponded with increased feelings of pleasure in males [ 42 ]. Foster, (2007) also found higher blood glucose accompanied increases in alertness and contentment when breakfast was consumed rather than omitted [ 43 ]; consuming a meal containing CHO prior to exercise may contribute to post-exercise mood state by increasing pre, and therefore post, exercise glycogen stores [ 17 ].

Worse performance on the RVIP task was observed mid-afternoon when the larger breakfast was consumed compared to the smaller breakfast or no breakfast and in the evening fewer RVIP errors were seen following consumption of the smaller breakfast compared to the other conditions. Although previous data suggests working memory is improved by prior breakfast consumption (for review see [ 27 ]), our data suggests that when consumed prior to exercise, a smaller, rather than larger, breakfast avoids detriments in working memory later in the day. These results somewhat mirror those found by Nabb and Benton (1996), who reported that memory score negatively correlated with the caloric content of the breakfast administered, attributing this to only minor increases in blood glucose following a smaller meal [ 44 ]. Indeed, recently Zilberter and Zilberter (2013) suggested that the belief that consuming breakfast is beneficial for cognitive function may be incorrect [ 45 ]. They argued that consumption of a low-CHO, high-fat breakfast or indeed omitting breakfast produces the most stable metabolic response, a factor which appears to contribute positively to cognitive function possibly via a neuroprotective effect. However, even though fasting may lead to a more stable metabolic response acutely, there is evidence that insulin sensitivity and glucose response to a meal are improved when breakfast has been consumed beforehand both acutely [ 46 ] and regularly [ 8 ].

It is perhaps surprising that cognitive differences were observed between the conditions when tasks were completed on the mobile phone but not when completed on a computer in the laboratory. Whilst the lack of cognitive effects in the initial post-exercise period does mirror previous laboratory based data [ 15 16 ] few studies have looked at the effect of breakfast consumption on cognitive function in the evening. A delayed effect of breakfast on cognitive performance, or of course a second-meal effect, whereby the effects of breakfast on cognitive performance only become apparent after the next meal has been consumed, are plausible given that the glycaemic index of an evening meal has been shown to affect cognitive function post-breakfast breakfast the following morning [ 34 ]. It has also been suggested that if breakfast is consumed regularly, omitting breakfast occasionally may not have a negative impact on cognitive performance; rather these effects may only be seen if breakfast is omitted over a long period of time [ 47 ]. In the current study, consuming breakfast lowered subjective appetite at every time point following breakfast up until immediately after lunch with the greatest differences observed between the NB and 40 g breakfast conditions, as expected. Whilst these results are not considered novel when viewed in isolation, the study also aimed to draw parallels between subjective appetite sensations and mood state and cognitive function. Indeed, the superior appetite profile seen following breakfast concurred with an improvement in at least one facet of mood at most time points throughout the study day; we reported a similar effect in a previous study in male subjects when enhanced appetite control occurred concurrently with lower mental fatigue ratings [ 16 ]. Breakfast can also positively influence appetite responses to a second feeding [ 46 ] but our data showed no effect of breakfast on appetite beyond immediately post-lunch; any effects were likely masked due to the ad libitum nature of the lunch meal.

Research shows that breakfast consumption can also reduce subsequent EI [ 46 48 ] although the effect of exercise on this parameter is debatable [ 49 50 ]. Previous data from our laboratory [ 12 ] revealed that breakfast consumption (451 kcals) compared to omission before exercise improved subjective appetite control, but did not affect EI at lunch following exercise in males. Similarly, lower subjective appetite ratings did not coincide with a reduction in EI at lunch or post-lunch in the current study. This could be due to a lack of power to detect EI effects when administering an ad libitum meal although other explanations should be considered. The majority of the sample in the current study were restrained eaters. The high prevalence of eating restraint in females [ 51 ] is consistently highlighted as a problem in this area of research, although there is data suggesting dietary restraint is not a reliable predictor of EI [ 52 53 ]. It should also be considered that post-lunch, participants were able to resume their normal diet; there may of course be an interactive effect of breakfast and exercise on subsequent EI, but not one which is robust enough to override everyday habitual behaviours [ 54 ]. It is also important to acknowledge here the well-known complications in gathering accurate food-intake information using food diaries [ 38 55 ], and this data should be viewed with this in consideration.

A limitation this study was the unconstrained environment in which the mobile phone tasks were completed and a variety of nutritional, behavioural and emotional factors may have influenced task performance and mood state at these times; this should be considered when interpreting the apparent negative effect that the smaller breakfast had on tension and mental fatigue in the evening. Nevertheless, this novel method is considered suitable for data collection of this nature [ 56 ] and the “free-living” data it provides is lacking in the literature and is useful to guide the direction of research and formulate future hypotheses. The breakfasts administered provided approximately 5% and 10% of the energy needs of a typical adult female, lower than recommended (between 20% and 35% of total daily energy needs [ 57 ]). However, the larger of the breakfasts administered in the current study was based on data from the pilot study where the average breakfast consumed was just 234 kcal and therefore perhaps reflects that typically consumed by the population of interest. It should also be noted that the both studies described in this paper used predominately student samples; therefore, this data may not be as valid for other populations.