In the West, approximately one out of every five employees works odd hours or night shifts. Studies have shown that, apart from generating attention or sleeping disorders, working at night can disrupt our metabolism in such a way as to cause weight gain.

Even if some people have a hard time adapting, the fact is that when our circadian day/night rhythm changes, as a result for example of a transatlantic flight, we have to gradually adjust to this change since light is the stimulant which modulates the melatonin cycle, the true sleep hormone. We also have to think of changing our mealtimes accordingly.

In the case of people who work night shifts, the influences they are subjected to are contradictory.  The external stimulants, such as light or mealtimes, perceived by night workers’ biological clocks do not coincide with their sleeping/ waking cycles.  

The fact that, in order to share with their families and for social reasons, these people adopt day rhythms on their days off or holidays makes for temporary adjustments.  The conflicting information thus received by their bodies alters their biological rhythm generating major and/or secondary hormonal and metabolic disorders which can result in significant chronobiological stress.

Studies have shown that cortisol secretory rates are much lower when working nights, precisely the time when the physical and mental effort exerted by night workers requires higher quantities of this hormone. 

Inversely, during their sleep, night workers secreted excessive amounts of cortisol which resulted in sleeping disorders. The fact is that cortisol variations, as in the case of the growth hormone, are one of the factors that regulate the glucidic metabolism and insulin secretion.

Tests carried out on night workers in Antarctica have shown that they have higher glycemia, insulin and postprandial lipidemia levels that which generates a resistance to insulin at normal mealtimes. Other studies had furthermore already observed higher triglyceride levels in these cases.

Thus, night workers or people who work different shifts run a much higher risk of gaining excess weight. Three prospective studies (among others, two dealing with nurses) have estimated that night workers’ Body Mass Indexes (BMI) is much higher than that of people who work during the day.