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Meal timings: do they matter?

Could something as simple as when we eat influence our body weight and health? That’s what Professors Alexandra Johnstone and Peter Morgan, of the Rowett Institute at the University of Aberdeen, are investigating. In the aptly named MRC-funded Big Breakfast Study, they’re aiming to distinguish whether meal timings are important – and if so, why.

Professors Peter Morgan and Alexandra Johnstone. Image credit: The Rowett Institute

Do you eat breakfast or usually skip this meal to rush to work, or to sleep for longer? If you don’t eat breakfast is it because you don’t feel hungry and can’t face food first thing? Not feeling hungry in the morning might be because you consumed a lot of calories before sleeping.

If you prefer to hit the snooze button, or eat much later in the day, you’re not alone. The most common pattern of eating in the UK is to consume most of our daily calories in the evening – roughly 40% of our daily energy intake – and fewer calories in the morning.

We know that what we eat may affect our risk of heart disease, high blood pressure, type 2 diabetes and obesity. Yet recent nutrition research is showing that when we eat may be just as important for health. So, does it really matter when you eat your largest meal?

Out of sync

Chrono-nutrition is an evolving and developing field of science which is beginning to show how our ancient biology is in conflict with our modern lifestyle. The mechanisms behind why time of eating may influence health are not entirely clear.

But an underlying principle is that our modern lifestyles are often led without any consideration of our body’s natural rhythms – known as ‘circadian’ rhythms. In the Big Breakfast Study we plan to look at how our biology and behaviours influence our body’s energy balance and weight, relative to when we eat.

By studying how our body uses energy throughout the day we’re aiming to find out whether eating a big breakfast (and a smaller evening meal) influences daily energy balance. This will help us understand the role of eating patterns in the control of body weight, an important consideration in the context of the rising obesity epidemic.

Do meal timings matter?

UK current healthy eating advice is based around the long-held assumption that ‘a calorie is a calorie’ and that meal timing is inconsequential. But different cultures have different approaches to eating, for example in Spain a larger midday lunch meal is commonly followed by an afternoon siesta and evening tapas (small plates of food).

Research has linked the eating style of late evening eating calories to weight gain and obesity and there is also evidence that eating breakfast is linked to a lower risk of obesity. This supports the theory that it’s better to eat your main meal earlier than later. But for the moment this still remains a hypothesis and it is not conclusive, since the idea is based on data from cross-sectional studies which cannot define cause and effect.

Getting to the root of the cause

From a physiological perspective, our body is used to us eating during the light period and sleeping during the dark period – this is ‘in sync’ with our circadian rhythms. These circadian rhythms are driven by our ‘body clock’ which determines when to sleep, rise, eat, as well as many other physiological processes. The master body clock is affected by environmental cues, particularly light and a change in time zone – but also when you eat. When the internal rhythms are out of sync with the environment, then you have something akin to ‘social jet lag’.

Since disruption of circadian rhythms usually has negative effects on health, we need to re-tune our lives with our body clock – eating when our body really needs food rather than when we have time. This is difficult with today’s work culture of ‘snackification’ – eating food on the go or grabbing a quick bite at a desk to multitask, rather than sitting down in a canteen to eat a meal.

The impact of irregular eating

As our lifestyles have become more irregular, then so have our meal patterns. Compared with 30 years ago, more meals are skipped, or eaten on the go and later in the day. Of particular concern is shift work, where people work during the dark and sleep during the daylight with irregular eating times. This has profound consequences on metabolic events in the body, with altered insulin sensitivity and higher body mass giving rise to increased risk of cardiovascular disease, type 2 diabetes and high blood pressure – all not good news.

It is of course the type of foods you choose and portion sizes that have the biggest impact on your health. But if the results of our study suggest that time of eating is linked to bodyweight and health, then this could help inform changes to dietary advice so that people consider not only nutritional content but also time of eating.

We’ve funded The Big Breakfast Study as part of our initiative to understand more about mechanisms in nutrition research.

Read more about MRC-funded nutrition research.

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