Why don't more people eat breakfast? A biological perspective

Dear Editor:

Nearly one-quarter of individuals in the United States skip breakfast daily, with an average energy contribution of ∼16% of total caloric intake. This is quite small in comparison to other meal times, such as evening (dinner) food consumption, during which ∼44% of daily calories are consumed (1). Prompted by such findings, a variety of studies have investigated the potential health benefits associated with breakfast consumption (2–4). In a recent article in this Journal, Chowdhury et al. (3) pointed out that the majority of the literature examining the impact of breakfast consumption on obesity relied on positive cross-sectional associations between breakfast omission and obesity. As such, they used a randomized controlled design and found that neither total caloric intake nor level of physical activity was different between obese individuals who consumed or skipped breakfast for 6 wk. However, the authors did note that fasting during breakfast time may decrease insulin sensitivity. This same group previously found that breakfast consumption was causally linked with an increase in physical activity thermogenesis and more stable glucose response in the remaining hours of the day in lean adults (4). Thus, there is an evolving understanding with regard to the importance of breakfast, with both epidemiologic and experimental data suggesting that breakfast consumption may be beneficial. However, the mechanisms that underlie these behavioral patterns, in our opinion, remain elusive within the literature.

It has been suggested that both personal (age, race-ethnicity, weight status) and geographical factors influence breakfast consumption when examining trends of US adults from 1965 to 1991 (2). All of these factors may play a role in an individual’s breakfast habits; however, this study does not mention the potential influence of biological rhythms, which indicate that human biology is not necessarily driven to eat in the early waking hours. As such, we propose that individuals who do not eat breakfast may not be biologically driven to do so, and that many people who do eat breakfast do so, perhaps, because of media-disseminated messages that underscore that breakfast is the most important meal of the day. Furthermore, we suggest that breakfast may be a healthy habit; however, interventions designed to increase breakfast consumption may need to consider this “biological drive,” which may be one of the primary factors influencing eating patterns.

A growing understanding of biological rhythms has provided evidence that behaviors may be governed by a multitude of internal and external clocks, which act as triggers and moderators for behavior and function (5). Pittendrigh (5) suggested that biological rhythms “exploit the challenges and opportunities offered by the periodic nature of the environment,” which is, perhaps, best shown by the sleep-wake cycle. Of interest in the present letter are patterns in diet, because these patterns are potentially influenced by oscillations originating from the suprachiasmatic nucleus of the hypothalamus, with further synchronization from both intrinsic (hormones) and external (light/dark cycle) oscillations.

With regard to diet, there is some indication that we may be more driven to eat food later in the day. For example, the endogenous circadian rhythm of hunger appears to peak in the evening (2000), with the nadir occurring around 0800 (6). This is supported by other rhythms, such as fluctuations in ghrelin, which influences hunger and appears to oscillate independent of food consumption (7). Specifically, Espelund et al. (7) found that ghrelin concentrations reached a peak around 1900, with a nadir occurring around 0400. In further support, leptin concentration increases overnight, reaching its nadir in the late afternoon (8). Because leptin is inversely associated with hunger, this provides some support for the notion that our physiology may be influencing these temporal differences in food consumption. This assertion is also supported by research that suggests that circadian rhythms play an important role in other health behavior–related activities. For example, Teo et al. (9) showed distinct differences in physical performance on the basis of circadian rhythms in core body temperature. This circadian rhythm-behavior relation is further supported by research that shows that physical activity behavioral manipulation can phase-shift an individual’s circadian rhythm (10). Within the context of dietary behavior, whether circadian rhythms of dietary triggers drive an individual’s desire to eat or skip breakfast, or whether the act of skipping breakfast phase-shifts these circadian rhythms of dietary and hunger triggers, is not explicitly clear (perhaps both play a contributing role). Clearly, this is an exciting and ripe area for future research, and we feel that this letter may help to spawn such necessary work.

The purpose of this letter is not to challenge the current literature but to suggest the potential importance of biological rhythms in the interpretation and approaches to breakfast consumption. In doing so, we may better understand the role of breakfast and design more effective interventions to promote breakfast consumption.