Matching meals to body clocks – optimising mealtime for health
In this blog you can read about body clocks and their role in optimising our health depending on the time we eat. We introduce some main areas of the research, both at the Rowett Institute and elsewhere, identifying that it may not only be what we eat but when we eat that effects our health. If you have time you can use the links within the blog to read the underlying research publications.
Anyone who has travelled to different time zones or pulled an all-nighter will experience that there are consequences of disrupting your natural body rhythm. A foggy brain, mood changes and inability to make clear decisions are just a few of the more notable short-term side effects linked to disruption of the natural sleep-awake cycle. However, ongoing research from the Rowett Institute has begun to show that disrupting this cycle, called the ‘circadian system’, can also cause changes in hormones and physiology which can contribute to health issues and weight gain in the long term.
What are Circadian Rhythms?
Circadian rhythms are the normal cyclical fluctuations that occur in humans’ biological processes within a ~24-hour period. These daily rhythms are aligned to the earth’s natural light/dark cycle and help you to sleep at night (promoted by the production of the sleep hormone melatonin) and wake up in the morning (promoted by increasing cortisol levels). However, the effects of the circadian system go far beyond these basics rhythms, also driving daily changes in metabolism, appetite, physical performance and cognitive function. The primary regulator of these rhythms is a tiny region in the brain called the suprachiasmatic nucleus, the so called ‘master clock’. It receives input from the eyes about the daily light/dark cycle and relays hormonal and behavioural signals to the rest of the brain and the body about time of day to help keep all the bodies tissues in sync.
Not only is there a master timekeeper in the brain, but also clocks within all cells in the body which regulate the timing of processes at a tissue level. This means there are clock cells in your heart, kidneys, pancreas, liver, skeletal muscle and even fat tissue. These tissues are involved in many important functions such as controlling energy metabolism and food digestion and it is essential they work in harmony to effectively regulate processes in the body.
So why are meal timings important?
Not only do circadian rhythms influence when we eat, but when we eat may alter our circadian rhythms. Delaying mealtimes by five hours, thereby missing breakfast and eating late at night before going to bed, saw changes in the timing of clock genes in fat tissue without changing the timing in the brain. Delaying mealtimes may also negatively affect blood sugar and hormone rhythms which were misaligned compared to early eating.
So what does this mean?
Other studies have now begun to link meal timing with metabolic health and body weight regulation. Earlier timing of food intake, eating a larger breakfast rather than a larger dinner, or consuming more calories in the morning are strategies which have shown to be better for weight loss. Eating earlier and avoiding late night meals and snacks has not been found to be beneficial in all studies, with some not seeing the effects of meal time on weight loss or glucose control. Work is continuing to understand how various meal timings may help improve health and weight.
How might it work?
Firstly, certain processes involved in nutrient digestion and metabolism are more optimal at certain times of the day and it makes sense to eat at these times. In the morning, due to our gut clock, our stomachs empty faster, and digestion is overall better due to more gastric juices and enzymes to break down a meal. The disruption of circadian rhythms effects our digestive system, as well as sleep disturbance, seen for example in night shift works, and can lead to gastrointestinal disorders.
Blood sugar is also regulated better in the morning, with a quicker and higher insulin response. Whereas eating at night results in poorer control of blood glucose, again this may have implications such as increased metabolic disease for people working at night.
Secondly, meal timing may reinforce or cause misalignment of circadian clocks. Regular meal timing may help to synchronise and amplify rhythms, whereas irregular, particularly late meals or night-time feeding may cause desynchronization and suppressed rhythms. Therefore, incorrect timing may result in mismatched signals in the body and possibly suppression of important hormones regulating energy expenditure and appetite. Equally a large meal before bed can increase gut hormones which may affect the quality and quantity of sleep. Poor sleep can also negatively affect circadian rhythms and hormones regulating energy expenditure and appetite.
So when should you eat?
We currently do not know the best time of day to eat, we do know that eating throughout the night is linked to higher risk of disease and obesity. Rowett research is currently investigating the effects of energy distribution throughout the day and its impact on weight loss and metabolic health as well as looking into the effects of shift work.
What we currently know is maintaining regular mealtimes, starting the day with a healthy breakfast and avoiding late night eating as well as maintaining regular healthy sleep habits, is likely to help reinforce circadian rhythms optimising our health.
Dr Leonie. C. Ruddick-Collins
Prof Alexandra. M. Johnstone
Prof Peter. J. Morgan
Funding Acknowledgements:
MRC: MR/P012205/1 The Big Breakfast study
Scottish Government Rural and Environment Science and Analytical Service Division (RESAS).