You are when you eat - how time of eating influences body weight
2022-12-28

Did you eat breakfast this morning, or skip this meal to rush to work, or to sleep longer? If you don’t eat breakfast, is it because you don’t feel hungry and can’t face food first thing?

If you prefer to hit the snooze button for a longer sleep, or choose to 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.

Not feeling hungry in the morning might be because you consumed a lot of calories before sleeping.

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?

Research shows that with the extra calories consumed across all the recent festive celebrations, that we can gain on average around 1kg (roughly 2lbs). With around 60% of the Scottish population collectively overweight and obese, it is recognised that we live in an ‘obesogenic environment’ where a sedentary lifestyle and ample supply of energy dense food means it is easy to gain weight (and difficult to lose weight). Habitual breakfast consumers tend to be leaner, perhaps because they also engage in other healthy behaviours that favour weight control, such as regular physical exercise.

There is no universal definition of a healthy breakfast. I consider it to be the first meal of the day that breaks the fast after the longest period of sleep and consumed within 2-3 hours of waking. People who skip breakfast often miss this meal to reduce calorie intake to control body weight. Ironically, research has shown that habitually skipping breakfast and opting instead to become an evening eater is associated with greater weight gain. The old-fashioned saying, ‘Breakfast like a king and dine like a pauper’, to eat more calories in the morning and less in the evening, perhaps has a grain of truth. Recent research has suggested that eating calories in the late evening leads to weight gain. But it is not clear cut and interestingly, we have recently reported, in a controlled diet study, that time of day of consuming calories does not influence energy expenditure and ability to achieve weight loss. Nonetheless, we suggest that for people seeking to lose weight, they are better able to control appetite with a bigger breakfast and smaller dinner regime.

This is also particularly relevant for people who work shifts, that weight loss is achievable regardless of time of calories consumed. In shift work, eating does not coincide with the natural light/dark cycle, and the natural biological rhythms do not match feeding times. From a physiological perspective, our body is used to us eating during the light cycle and sleeping during the dark cycle – this is ‘in sync’ with our circadian rhythms. These circadian rhythms are driven by our ‘body clock(s)’ and this determines when to sleep, rise, eat, as well as many other physiological processes. The master ‘body clock’ in the brain is affected by environmental cues, particularly sunlight and a change in time zone – but also when you eat. This new field of research is called ‘chrono-nutrition’ which links time of eating with biological rhythms.

The mechanisms behind why time of eating may influence health are not entirely clear. 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. It is of course the type of foods you choose and portion sizes that have the biggest impact on your health. But if it is the case that time of eating is linked to bodyweight and health, then we should be able to give better dietary advice to people not only related to nutritional content but also on time of eating.

Published by News, University of Aberdeen

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