Is eating at the wrong time a handicap for our biological clock?

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Less attention has been paid to an important aspect of nutrition: when are we eating? [Shutterstock]

Herbalife Nutrition, a global nutrition company, whose purpose is to make the world healthier and happier, commissioned a special series of articles from us to explain the importance of the biological clock for wellness, how nutrition needs to be carefully timed and how the biological clock is directly linked to a healthy, active lifestyle.

By Ángeles Rol, PhD and Juan Antonio Madrid PhD, Chronobiology Laboratory, University of Murcia, Spain.

In developed societies, the incidence of overweight, obesity and metabolic diseases is continuously increasing. Highly sedentary lifestyles, together with easy availability to high-energy, processed foods, are the two main reasons that could explain this epidemic. Until now, research to address this problem has focused on analysing the impact of diet composition by asking: what are we eating?  However, less attention has been paid to another aspect of nutrition: when are we eating?  The chrono-biology of eating behaviour deals with this topic by studying the influence of our eating schedules on our metabolism, their regularity and which nutrients we’re eating at different times of the day.

We know that delaying meals, in particularly eating late, is associated with an increased risk of overweight, obesity, metabolic and sleep disorders. Some nutrients can make us feel worse or better depending on when they are ingested. This is the case of sugars, since when ingested at night, produce a higher increase in blood glucose due to insulin resistance that occurs naturally during the nocturnal fasting period.

Traditional meals at fixed hours in a familiar environment are progressively being shifted towards more irregular feeding patterns outside the home with pre-processed food. Could this habit change be affecting our health? The answer is totally affirmative. To understand why, it is important to understand two fundamental characteristics of the ‘circadian biological clock’. The first one is that the clock needs to be set, day-by-day, by periodic environmental signals (so-called synchronizers or zeitgebers) and this includes the ‘light-dark’ cycle and regular meal timing. In the absence of synchronizers, rhythms become out of sync with the 24-hour environmental cycle.

The second one is that of the biological clock’s function to allow physiological processes to anticipate these periodic events that occur in our habitual life. Thus, the circadian clock prepares us for waking and getting up in the morning, making it a less traumatic process while predicting the precise moment at which we are going to eat. If eating always takes place at the same time, the circadian clock will activate gastrointestinal motility and digestive secretions in advance, and then, when food is ingested, digestion, nutrient absorption and metabolic processes can be performed with maximum efficiency. Meal irregularity hinders circadian clock synchronisation and prevents its anticipatory function.

Therefore, it is not surprising that those studies experimentally addressing the impact of meal timing irregularity have shown consistent results in relation to health. So, when we skip meals and/or these occur at irregular times, several unhealthy symptoms have been reported: i) the thermogenic effect of food decreases (this is a transitory increase in the caloric expenditure that occurs after intake); therefore we will burn fewer calories; ii) increases in hunger sensation, partly as a consequence of reducing the levels of peptide YY (a satiety signal) in response to food intake; iii) worsens the control of glycaemia, both in healthy and in diabetic subjects.

In addition, epidemiological studies conducted in large populations have shown that people who eat irregularly are more likely to suffer metabolic syndrome, insulin resistance (insulin released in response to food produces less effect, and then blood glucose increases) and cardiovascular events.

Therefore, regular eating schedules will enhance circadian clock synchronisation and will fulfil its anticipatory function improving digestive and metabolic efficiency.


  • Alhussain MH, Macdonald IA, Taylor MA. Irregular meal-pattern effects on energy expenditure, metabolism, and appetite regulation: a randomized controlled trial in healthy normal-weight women. Am J Clin Nutr. 2016;104(1):21-32.
  • Sierra-Johnson J, Undén AL, Linestrand M, Rosell M, Sjogren P, Kolak M, De Faire U, Fisher RM, Hellénius ML. Eating meals irregularly: a novel environmental risk factor for the metabolic syndrome. Obesity (Silver Spring). 2008;16(6):1302-7.
  • López A, Rol MA, Madrid JA. Ritmos biológicos en la nutrición y el metabolism. In “Cronobiologia Básica y Clínica”. Edite@red. Madrid 2006.

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