Chrononutrition & Shift Work: Research versus Reality

Chrononutrition marries the study of circadian biology and nutrition. It is a rapidly evolving field of research, with many interesting papers coming out in the last few years alone. Our internal biological clock can hugely impact upon our nutrition. However, nothing will fuck with your internal biological clock like some good old-fashioned shiftwork. Having done my fair amount of shiftwork (and currently typing this from a 20 hour shift!), I thought it would be interesting to compare the recommendations from the research against my own reality.

I would caveat my conclusions from the research by saying I am by no means an expert in any of this. I am merely inferring my interpretation of the research with my own experience. Better educated people than myself have produced more detailed articles and information. Sigma Nutrition’s Danny Lennon has written a fantastic article on chrononutrition (click here), that is an excellent starting point. Furthermore, Alan Flanagan (@thenutritional_advocate) possesses a wealth of knowledge on the subject, with particular focus on shift workers.

Chrononutrition: Overview

Chrononutrition is detailed and multi-faceted, and anything beyond the basic extends far beyond the capacity of my simple brain. I will detail below my interpretation of the main components of chrononutrition. Hopefully, the fact that I can understand the basics mean you will most certainly grasp the key concepts.

Thus concludes our intense three paragraph course on chrononutrition.

Circadian Rhythm

Circadian rhythm is king. In essence, it is what controls our natural sleep-wake cycle. Human circadian rhythm revolves around a roughly 24 hour window. We react to the changes in light (or lack of) in our environment. This can affect our biological processes, and the study of this is creatively named chronobiology.

Our circadian rhythm is autonomous (we don’t need to consciously regulate it). Its regulation is assisted by cues in our environment called zeitbegers. Sunlight, exercise and feeding are just some examples of influencing factors.

In mammals (that’s us), the main markers of our circadian rhythm timing are: melatonin, our core body temperature and cortisol levels. Our normal melatonin level is quite low during daytime, and will rise quickly in the evening, continue to rise during the night and then returns to baseline around dawn[1]. Cortisol is a hormone released in response to stress. It is naturally high in the morning, drops sharply after you wake up, and continues to fall until evening. Cortisol is a vital regulatory hormone for us, having a knock-on effect on immune function, metabolism and our mood[2].  

What causes disruption to both melatonin and cortisol levels you ask? Staying awake all poxy night on a shift is the answer. How exciting. Hopefully from this exceptionally brief overview, you can at least appreciate that our sleep-wake cycle is involved in a RAKE of our body processes, and can be easily disrupted by shiftwork.


What we eat has a huge impact on our body. Certain foods can impact our body differently, which is a simple concept to grasp. The buzz you feel after a HEAP of pints is far different than the despair of a kale salad (though each has their place). When we eat (meal timing), what we eat (macros bro) and how we process that (digestion) hugely influences our hormones, mental and physical health[3]. Therefore, it stands to reason that our nutritional protocols and strategies can influence our circadian rhythm, no?

Chronodisruption: The Chicken/Egg Fallacy

Chronodisruptors refer to factors that negatively influence the synchrony of our body clock. In essence, everything was going grand until these bad boys showed up. Herein lies the great question: does eating mess up your circadian rhythm or does your circadian rhythm influence your eating?

The answer is both. It’s never straight-forward, is it?

The Research & The Reality

With our intensive three paragraph course on chrononutrition completed, it is time to delve into the recommendations from the research, and how you can implement them (or how you absolutely cannot, sorry science). Science is not always practical. The recommendations for “gold-standard” practice is often at odds with reality. From my scanning of the research, I have listed the main recommendations from the research for minimising the potential damage from ill-structured nutritional protocols.

Strategy #1: Front-Load Your Calories

Front-loading your calories involves eating the majority of your daily energy intake during the first part of your day. It basically refutes the claim that meal timing is irrelevant, and the emerging research seems to support this.

Why would this help?

It may be an idea to front-load your calories on a shift, as the research points to it being a more effective means of reducing the disruption to the biological clock. Some studies, (albeit with very small sample sizes) have shown that diet-induced thermogenesis (thermic effect of feeding [TEF]) to be up to 50% lower in the evening than in the morning[4]. Therefore, as we are burning less calories when we digest the food in the evening, we will store more energy when we consume calories at night. 500 calories consumed at 6am and 500 calories consumed at 6pm will be processed differently, if this research is accurate. (However, I would argue that with TEF only accounting for roughly 10% of general population energy expenditure[5], it’s nothing to get too excited about. It won’t make or break your energy balance, but it is certainly worth bearing in mind.)

Morning calorie consumption is also linked to more optimal insulin and triglyceride levels, and improved glycaemic control[6]. Again, this is largely an individual response, and calorie consumption in the morning isn’t the sole influencing factor on these levels. But it is something to bear in mind.

Shiftworkers tend to eat a significant amount of food when the typical person is sleeping, AKA during the biological night. Therefore, it is possible that incorrectly timing your eating patterns on a shift can contribute to health problems associated with shift work. Obviously, one must also consider the tendency amongst shiftworkers to consume more hyperpalatable, less nutrient-dense foods, be less physically active and have disrupted sleeping patterns. It is not possible to infer that timing alone is responsible for these outcomes, but I would certainly consider it a contributing factor based on the research.

What does this mean for shift-workers?

I would suggest that if you are to go off this research, it may be wise to eat most of your calories in the first few hours of your shift, or have a big meal right before your shift. I would consider this a relatively easy suggestion to implement for most shiftworkers, and is a strategy I use myself. If I am on a night-shift, I will typically eat a big dinner right before I start.

It may be of benefit to bring one big meal in with you, and eat it as soon as you can, potentially during your first break on your shift.

Strategy #2: Time-Restricted Feeding

Time-restricted feeding (TRF) simply means eating ones caloric intake during a defined time period. You may have heard people following dietary protocols such as intermittent fasting, or people not eating carbohydrates after 6 pm etc. The reasoning behind these protocols aside, they simply serve as examples of time-restricted feeding.

What can TRF do for me?

The impact of TRF on health in humans is relatively under-researched. There is some evidence in animal studies to suggest it may be beneficial in reducing bodyweight and cholesterol levels, whilst keeping caloric intake constant[7]. Small studies on TRF in humans found it beneficial in reducing total caloric intake[8].

What does this mean for shiftworkers?

The participants did find it difficult to adhere to TRF protocols.I would imagine that this would be particularly difficult to follow during shift-work, as many shifts do not have set breaks. I know from personal experience that certain shifts I carry out are impossible to guarantee I will be able to eat at a certain time. I know for a fact that if the eating window I set myself “closes” before I have had time to adequately fuel myself because work has been flat out, the potential marginal health impact of breaking this fasting window pales in comparison compared to the burning hanger I feel.

If you like the idea of intermittent fasting, or your shift has guaranteed breaks, it may be worth a shot. But I know for many healthcare shifts, it’s just not pragmatic.

Strategy #3: Timing Your Macronutrients Around Sleep

This is where the literature gets a bit fuzzy. Many studies have found a correlation between the last meal we eat and good sleep quality[9,10,11]. However, many of the studies I found used relatively small sample sizes (20 participants), making it therefore difficult to generalise these results across the wider population. Furthermore, I struggled to find controlled studies that examined the hypothesis that food can be a zeitgeber in humans (if you find one, please send it my way!). And as always, correlation does not imply causality. In the absence of these controlled trials, it is impossible to ascertain whether foods can directly influence our circadian rhythm.

So, there’s no direct evidence. Why did you list this as a strategy?

Whilst we cannot directly link food timing and sleep quality, we are not entirely clueless.

Consuming a high-carbohydrate meal 4 hours before sleeping has been shown in one study to shorten the time it takes to fall asleep[12]. Another study found that high-protein diets were associated with less interruption to sleep, and further supported the claim that high-carbohydrate diets before sleeping are associated with shorter sleep time[10].

Eating close to bedtime is likely a no-no[13]. I would hypothesise that it is probably unwise to gear your body up for digesting a massive meal right before you intend to shut down into sleep mode. Again, this is largely speculation from me. In addition, I would imagine that our lesser glycaemic control in the wee hours could potentially be further detrimental to our health if we insisted on eating right before sleep time. I think this is far better explained in the SBS article, rather than my rambling.

What does this mean for shiftworkers?

This is a good question. I would imagine that it is probably wise for us shiftworkers to eat our last meal about 4 hours before we intend to sleep. As tempting as it is to get a scone or a pastry on the way home after a long shift, it can potentially affecct our sleep quality. And after a nightshift in particular, you NEED all the sleep you can get.

Strategy #4: Avoiding Erratic Eating Patterns

Now this is largely anecdotal, and behavioural. Preparation is king here. Shift work is unique and varied. Be it long days, night shifts or somewhere in between, once you know what you’re working with, it becomes easier to deal with and account for. The majority of Irish shift workers fail to meet the minimum requirements of the healthy eating guidelines. Low intake of fruit and vegetables and wholegrains are major issues[14]. You can guard against this, by ensuring you have prepared meals that will satiate you and hit all your nutritional targets. It might be worthwhile drafting a list of meals on your phone that are easy to prepare or assessing the menu of your workplace facilities for foods that will support you in achieving your goals.

Irish guidelines for shift workers recommend “tailoring your individual work circumstances to encourage regular meal patterns”[14]. If you work shifts, this will likely be as hilarious as it is impossible. As one cannot force a patient arresting to wait until you have finished your scheduled mealtime, it is important to be flexible in your approach.

What does that mean for the lowly shiftworker like me?

Be flexible. And as the Scouts would say, be prepared. Do the best you can with what you have.


If you made it this far, congratulations. In essence, shiftwork probably isn’t the best for you. Timing your food can be difficult, and best practice can be hard to follow. Doesn’t mean it’s impossible. My take-home advice, from scalping the literature and anecdotal experience is as follows:

  1. Try and eat the majority of your meals earlier in your shift.
  2. Try and stick to regular meal timings.
  3. Eat regular meals where possible.
  4. Eat a big meal before your shift.
  5. Plan your meals before your shift.
  6. Pack meals you can re-heat in work and snacks you can easily eat.

Finally, I am by no means an expert on this AT ALL. Please let me know if there is something incorrect, confusing or stupid.


  1. Benloucif, S., Guico, M.J., Reid, K.J., Wolfe, L.F., Zee, P.C. (2005) ‘Stability of Melatonin and Temperature as Circadian Phase Markers and Their Relation to Sleep Times in Humans’, Journal of Biological Rythyms. Available at:
  2. Adam, E.K., Quinn, M.E., Tavernier, R., McQuillan, M.T., Dahlke, K.A., Gilbert, K.E. (2017) ‘Diurnal Cortisol Slopes and Mental and Physical Health Outcomes: A Systematic Review and Meta-analysis’, Psychoneuroendocrinology. Available at:
  3. Khan, A., Ullah Khan S., Khan, S., Zia-Ul-Islam, S., Khan Baber, N., Khan, M. (2018) ‘Nutritional complications and its effects on human health’, Journal of Food Science and Nutrition. Available at:
  4. Morris, C.J., Garcia, J.I., Myers, S., Yang, J.N., Trienekens, N., Scheer. F.A. (2016) ‘The human circadian system has a dominating role in causing the morning/evening difference in early diet-induced thermogenesis’, Obesity. Available at:
  5. Westerterp, K.R. (2004) ‘Diet induced thermogenesis’, Nutrition & Metabolism. Available at:
  6. Ruddick-Collins, L.C., Johnston, J.D., Morgan, P.J., Johnstone, A.M. (2018) ‘The Big Breakfast Study: Chrono‐nutrition influence on energy expenditure and bodyweight’, Nutrition Bulletin. Available at:
  7. Sherman, H., Genzer, Y., Cohen, R., Chapnik, N., Madar, Z., Froy, O. (2012) ‘Timed High-Fat Diet Resets Circadian Metabolism and Prevents Obesity’, FASEB. Available at:
  8. Antoni, R., Robertson, T.M., Robertson, M.D., Johnston, J.D. (2018) ‘A pilot feasibility study exploring the effects of a moderate time-restricted feeding intervention on energy intake, adiposity and metabolic physiology in free-living human subjects’, Journal of Nutritional Science. Available at:
  9. St-Onge, M.P., Mikic, A., Pietrolungo, C.E. (2016) ‘Effects of Diet on Sleep Quality’, Advances in Nutrition.Available at:
  10. Lindseth, G., Lindseth, P., Thompson, M. (2011) ‘Nutritional Effects on Sleep’, Western Journal of Nursing Research. Available at:
  11. Yajima, K., Seya, T., Iwayama, K., Hibi, M., Hari, S., Nakashima, Y., Ogata, H., Omi, N., Satoh, M., Tokuyama, K. (2012) ‘Effects of Nutrient Composition of Dinner on Sleep Architecture and Energy Metabolism during Sleep’, 年. Available at:
  12. Afaghi, A., O’Connor, H., Chow, C.M. (2007) ‘High-glycemic-index carbohydrate meals shorten sleep onset’, American Journal of Clinical Nutrition. Available at:
  13. McHill, A., Phillips, A.J., Czeisler, C.A., Keating, L., Yee, K., Barger, L.K., Garaulet, M., Scheer, F.A., Klerman, E.B. (2017) ‘Later Circadian Timing of Food Intake Is Associated With Increased Body Fat’, American Journal of Clinical Nutrition. Available at:
  14. Safefood (2016) ‘Managing food on shift work An exploration of the eating patterns, related lifestyle behaviours and experiences of shift workers on the island of Ireland’. Available at:

Published by Michelle Carroll

I am an online coach (MSc Sports & Exercise Nutrition, EQF Level 4 Personal Trainer, PN Level 1) and radiographer (BSc). I believe in empowering others to make better choices for their health through education. I think that the fitness industry has created a disconnect between best practices and “evidence-based” practices. I hope by chronicling my experience as a healthcare professional and my education as a fitness professional I can assist others on the path to bettering themselves.

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