The delicate dynamics of circadian rhythm and eating habits

Circadian rhythms are the internal biological clocks that regulate various physiological processes over a roughly 24-hour cycle. They govern sleep-wake patterns, hormone secretion, cognitive performance, food intake, exercise, and, ultimately, long-term health outcomes. 

Disruptions to the circadian rhythm from issues like jet lag and shift work may significantly impact your patients’ eating behaviors and metabolism. Fortunately, understanding this relationship will help you to be better equipped with practical solutions.

Tinkering with the internal timekeeper

A review article published in the International Journal of Molecular Sciences provides an overview of the circadian system and its interaction with nutrition and metabolic health.^[]

The circadian rhythm influences sleep-wake cycles, hormone secretion, body temperature, and cellular repair mechanisms. It’s regulated by a region of the brain called the suprachiasmatic nucleus (SCN). This master clock synchronizes the body's functions with the natural day-night cycle. Environmental cues like light exposure, food intake, and exercise help our bodies "keep time."

Circadian misalignment happens when external cues to the peripheral clocks conflict with the SCN’s sense of time (such as bright lights in the evening), mixing up crucial signals and interfering with body processes.

Metabolism regulation

Research has shown that our bodies have evolved to metabolize nutrients more efficiently during specific times of the day—namely when it’s light out. The expression of genes involved in digestion, absorption, and metabolism of nutrients follows a circadian pattern.

Insulin release and glucose tolerance peak during daylight, suggesting that the body is better equipped to handle glucose in the morning.^[] Indeed, several studies have linked better long-term weight control with the practice of eating more calories early vs later in the day, according to the authors of an article on chrononutrition.^[] This aligns with the traditional wisdom of having a hearty breakfast to provide your body with the necessary fuel for the day ahead. Conversely, in the evening, insulin sensitivity tends to decrease, making late-night snacking less metabolically advantageous.

Researchers gave 10 healthy young men isocaloric meals for breakfast, lunch, and dinner. Meals were provided at 5-hour intervals throughout the day. Over the first 6 days, the first meal was served early (within a half hour of waking). During the remaining 6 days, breakfast was delayed 5.5 hours after waking.

While photic cues are considered the primary SCN regulator (marked by melatonin and cortisol levels), investigators concluded that eating times are a variable that can be used to influence peripheral circadian rhythms. In this study, plasma glucose rhythms were delayed in concert with the delay of the first meal. Shifting to the later meal schedule also coincided a 1-hour delay in WAT PER2 expression, indicating that “feeding patterns may be capable of synchronizing human peripheral clocks,” according to the study authors (a phenomenon previously demonstrated in animal studies).

Repercussions of disrupting the clock

Irregular eating patterns, such as skipping meals or consuming large meals late at night, can lead to circadian misalignment and associated health problems.

Circadian misalignment occurs when our eating habits and other environmental factors are out of sync with our biological clocks. This dissonance can have far-reaching implications for metabolic health. The International Journal of Molecular Sciences authors cite studies that have linked irregular eating patterns with increased risks of obesity, insulin resistance, and cardiovascular diseases. Additionally, disruptions in circadian rhythms have been associated with disturbances in appetite-regulating hormones, leading to a higher propensity for overeating, poor food choices, and weight gain.

Getting on track for optimal health

Emerging research is shedding light on the concept of nutrient timing, which suggests that when we eat may be just as important (or even more important) as what we eat. Humans are designed to sleep when it’s dark and be active and eat during the daytime. 

Growing evidence suggests that restricting food intake to a defined window (time-restricted feeding) may offer metabolic benefits. This practice, also known as intermittent fasting, can be used to align with the body's natural circadian rhythm for improved insulin sensitivity, weight management, and overall metabolic health.

If lifestyle factors like shift work and jet lag can’t be avoided, it’s possible that careful meal timing, light exposure, and melatonin supplements could help bridge the gap and protect against some of the negative health effects of circadian disruptions.