Researchers studied how night shifts and eating at night affect cortisol, a hormone that controls many body functions and normally follows a daily rhythm. They had 52 young, healthy adults simulate working four night shifts in a lab, with some eating a meal, some eating a snack, and some eating nothing at midnight. They found that eating anything at night increased cortisol levels, and working multiple night shifts in a row shifted when cortisol peaked and dropped. This suggests that combining night work with nighttime eating could stress your body in ways that might cause health problems over time.

The Quick Take

  • What they studied: How eating at night and working night shifts affect cortisol, a stress hormone that your body normally releases on a schedule
  • Who participated: 52 healthy young adults (average age 24.5 years) who didn’t normally work night shifts. They were randomly assigned to eat a meal, eat a snack, or eat nothing at midnight during simulated night shifts
  • Key finding: Both eating a meal and eating a snack at midnight increased total cortisol levels compared to not eating. After four consecutive night shifts, cortisol patterns shifted—it was higher in the evening and lower in the early morning than on the first night
  • What it means for you: If you work night shifts, eating during your shift may increase stress on your body. The more nights you work in a row, the more your body’s natural rhythm gets disrupted. This may increase health risks over time, though more research is needed to confirm long-term effects

The Research Details

This was a controlled laboratory study where researchers carefully watched what happened to 52 healthy young adults during simulated night shifts. The participants were randomly divided into three groups: one group ate a full meal at 12:30 AM, another ate a smaller snack at the same time, and a third group ate nothing. Everyone completed four consecutive simulated night shifts, and researchers measured cortisol levels about once per hour throughout each night, with extra measurements taken 30, 60, and 120 minutes after eating.

The meal and snack had similar nutrition—about half carbohydrates, one-third fat, and one-sixth protein, with 23 grams of fiber. This allowed researchers to see if the amount of food mattered or if eating itself was the issue. The study was part of a larger research project, and this particular analysis focused specifically on how cortisol changed with eating and night shifts.

Understanding how night shifts and eating patterns affect cortisol is important because cortisol controls many body systems including metabolism, immune function, and inflammation. When cortisol patterns get disrupted, it can affect sleep quality, metabolism, and potentially increase disease risk. This study used a controlled lab setting, which means researchers could carefully measure cortisol without other factors interfering, making the results more reliable than just asking people about their experiences

This study has several strengths: it was a randomized controlled trial (the gold standard for research), used precise hourly measurements of cortisol, and controlled the environment carefully. However, the sample size was relatively small (52 people), all participants were young and healthy, and the study only lasted four nights in a lab setting. Real night shift work happens over months or years, so we don’t know if these effects continue or get worse with longer exposure

What the Results Show

Eating at night significantly increased cortisol levels. The group that ate a full meal at 12:30 AM had higher total cortisol output than the group that didn’t eat (this difference was statistically significant). The snack group also had higher cortisol than the no-meal group, and the difference was even more pronounced.

Working four consecutive night shifts changed when cortisol peaked and dropped. On the fourth night, cortisol levels at 8 PM were significantly higher than they were on the first night. Meanwhile, cortisol levels at 5:30 AM were significantly lower on the fourth night compared to the first night. This shows that the body’s natural cortisol rhythm was shifting as the nights went on.

These findings suggest that the body treats nighttime eating as a stressor, triggering more cortisol release. Additionally, consecutive night shifts appear to gradually shift the body’s cortisol rhythm, which could indicate that the body is struggling to adapt to the unusual schedule.

The study showed that both the meal and snack conditions produced similar cortisol increases, suggesting that the act of eating at night matters more than the amount of food. The temporal shift in cortisol rhythm across four nights indicates that the body doesn’t quickly adapt to night shift work—instead, the disruption appears to accumulate night after night

Previous research has shown that cortisol normally follows a daily pattern, highest in the morning and lowest at night. This study confirms that eating at night disrupts this natural pattern, which aligns with other research showing that eating at unusual times stresses the body. The finding that consecutive night shifts shift cortisol timing supports earlier studies suggesting that the body struggles to adapt to shift work, even over just a few days

The study only included young, healthy adults, so results may not apply to older people or those with health conditions. All participants were new to night shift work, so we don’t know if people who regularly work nights might adapt differently. The study only lasted four nights in a controlled lab, not the weeks or months of real shift work. Additionally, the sample size was relatively small, and the study didn’t measure other important factors like sleep quality or how participants felt

The Bottom Line

If you work night shifts, try to avoid eating large meals or snacks during your shift when possible (moderate confidence). If you must eat, keep portions small. Maintain consistent sleep and wake times even on days off to help your body maintain its rhythm (moderate confidence). Discuss shift work strategies with your doctor, especially if you work night shifts regularly (general recommendation)

Night shift workers should pay attention to these findings, particularly those working multiple consecutive nights. Healthcare workers, factory workers, security personnel, and others with night shift schedules may benefit from adjusting their eating patterns. People with existing sleep problems or stress-related conditions should be especially cautious. This study doesn’t apply to people who work regular daytime schedules

The cortisol changes happened immediately—within hours of eating at night and within the first few nights of shift work. However, the long-term health effects of these changes aren’t clear from this study. It may take weeks or months of repeated night shift work for significant health impacts to develop, though this research suggests the disruption starts right away

Want to Apply This Research?

  • If you work night shifts, track your eating times and sleep quality. Note what time you eat during shifts and rate your sleep quality (1-10) the following day. Over 2-4 weeks, look for patterns between eating timing and sleep quality
  • Set a personal rule: if working a night shift, eat your meal or snack before 11 PM or after 4 AM when possible, avoiding the midnight-to-4 AM window. Use app reminders to help stick to this schedule
  • Weekly check-in: compare sleep quality, energy levels, and mood on weeks when you minimize nighttime eating versus weeks when you eat more during shifts. Track this for at least 4 weeks to see if patterns emerge

This research is preliminary and based on a small study of young, healthy adults in a controlled lab setting for only four nights. The findings suggest potential concerns but don’t prove that night shift eating causes long-term health problems. If you work night shifts and have concerns about your health, sleep, or stress levels, consult with your healthcare provider. This information should not replace medical advice. Individual responses to shift work and eating patterns vary significantly, and what works for one person may not work for another.