Reply to SL Buckner et al.

Dear Editor:

We thank Buckner et al. for their insightful comments on the developing evidence base with regard to breakfast consumption and health. Specifically, the authors emphasize the potential influence of biological rhythms in determining breakfast habits and whether breakfast consumption or skipping, in turn, affects these biological rhythms. We wholeheartedly agree that these are important questions that warrant further investigation.

The influence of circadian rhythmicity on all manner of physiologic responses has long been established. There is a large body of evidence that suggests that the circadian system affects metabolic pathways and that changes in nutritional status can, in turn, alter circadian rhythms (1). As highlighted by Buckner et al. in their letter, appetite regulatory hormone concentrations change throughout the day and the biological rhythm of hunger varies according to time of day. In our recent investigations published in this Journal we examined the effects of free-living, extended-morning, fasting/breakfast consumption interventions on all components of energy balance and associated health outcomes in lean (2) and obese (3) populations. These experiments had a strength of examining the impact of differing morning feeding patterns within the context of normal life in which numerous factors affecting food intake (both metabolic-homeostatic and cognitive-hedonic processes) are in play (4). However, because of the nature of these investigations, the role of biological rhythms was not a focus.

Nevertheless, as part of our wider program of work examining breakfast consumption (5), we were also keen to examine underlying physiologic processes after differing morning feeding patterns. In crossover laboratory experiments conducted in both lean (6) and obese (7) individuals, we compared extended-morning fasting with the consumption of a typical carbohydrate-rich breakfast. These studies shed light on the acute effects of different morning feeding patterns, with evidence of second-meal effects on insulin, greater anorectic hormone response (increased peptide tyrosine tyrosine and leptin in the afternoon), and a paradoxical lack of suppression of ghrelin after a lunch preceded by breakfast. We therefore showed that, against the backdrop of underlying circadian rhythms for these hormones, morning feeding pattern affects the concentrations of these hormones during the day. Although more research is required to further examine the metabolic-homeostatic responses to acute breakfast consumption and omission, it is hoped that this work goes some way toward answering one of the questions posed by Buckner et al.: skipping breakfast does indeed acutely affect hormonal dietary triggers.

A second theme that the authors raise is the issue of whether circadian rhythms might be influencing an individual’s propensity to eat or skip breakfast. This is an interesting and important question, but one that is surprisingly difficult to answer. Some recent investigations examined hormonal and metabolic responses to breakfast consumption/morning fasting in groups defined by their breakfast consumption habits (8, 9). Unfortunately, notwithstanding inherent difficulties in defining what constitutes a breakfast consumer or skipper, these studies were based on self-selected breakfast habits and therefore it is difficult to assess causality. For example, where differences are observed, it is not possible to untangle the effect of breakfast consumption per se from other factors that might be different between groups (breakfast consumers tend to exhibit healthy behaviors). In addition, there is no way of knowing whether appetitive responses observed contributed to, or are a product of, an individual’s habitual morning feeding pattern. Further studies from our research program (5) aim to address if prolonged daily breakfast consumption/omission affects acute hormonal/metabolic and appetite responses on a given day. It is hoped that these results will give some insight into whether a randomly assigned daily morning feeding pattern results in entrainment of the appetitive regulatory system.

In conclusion, we agree with Buckner et al. that the roles of the circadian system in influencing dietary behaviors certainly warrant further study. However, it is also important to keep in mind that circadian rhythms are one of a number of factors that influence dietary behaviors. We would also caution that based on the current state of causal evidence relating to breakfast consumption (10), it is a little premature to be designing interventions to promote breakfast consumption for the general public. Much like our understanding of the role of circadian rhythmicity in breakfast consumption, our understanding of the influence of breakfast consumption on health still requires further development. In the future, with an accumulating understanding of the causal role of morning feeding on different elements of health, we might hope to be able to provide nuanced guidance for individuals to decide whether or not to eat breakfast.