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Not just what you eat but when you eat

Not just what you eat but when you eat influences body weight. Some of the recent science relating to this topic are being explored on 12th November, 2018 at The Royal Society of Medicine: Chrono-Nutrition-circadian clocks, mealtimes and metabolic disorders meeting. 

When you wake up in the morning, do you think about what to eat for breakfast or do you delay the first meal of the day to press the snooze button to sleep longer ? 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?

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. Historically an approach to healthful eating was proposed by Maimonides (1135–1204), a medieval Jewish philosopher and doctor. In his writings, he gave clear instructions regarding what, when, and how much people should eat in order to lead a healthy life. One of his well-known quotes is: “Eat like a king in the morning, a prince at noon, and a peasant at dinner.” There may be a grain of truth in this advice which linked time of eating and health outcome. The mechanisms behind why time of eating may influence health are not entirely clear.

Both nutrients and meal timing can affect our internal clock system, thus ‘chrono-nutrition’ has two aspects:

1) nutrients/food components regulate the clock system, e.g., caffeine prolongs the period of circadian clocks and the locomotor activity rhythm, and high-fat diets alter the rhythms of lipid metabolism, locomotor activity, and feeding behaviour;

2) meal-timing affects output of the clock system, e.g., skipping breakfast and nocturnal eating increases risk of obesity, whereas time-restricted feedings prevent metabolic disorders induced by high-fat diets.

Regular/time-restricted feedings synchronize and amplify the rhythms of clock system, whereas irregular/unusual feedings cause desynchronization and attenuate the rhythms, probably leading to metabolic disorders – this is particularly relevant for shift workers who have to eat when it is dark and the body is expecting to rest and restore.

We live in an ‘obesogenic environment’ where the working population eat up to two meals a day at a desk and this often means eating breakfast on the go. Our lifestyle choices associated with eating behaviour and physical activity contribute to the development of obesity.  Starting the day with quality nutrition may impact on your food choices later in the day; start as you mean to continue. Although habitual breakfast consumers tend to be leaner, targeting one eating episode (breakfast time) has provided to be largely unsuccessful for weight control. We need to consider the whole diet rather than single foods or meals. An occasional croissant or Danish pastry is not going to make you obese in one meal, but consuming energy dense foods along with a sedentary lifestyle, over time, will.

As we understand this interaction of time of day and metabolism better, we will be able to give more accurate dietary advice to the individual that is not only related to nutritional composition, but also time of eating. But first, we need more chrono-nutrition research (time of eating linked to circadian rhythm) to fill in some of the gaps in our knowledge.

Professor Alexandra Johnstone
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5 years ago

Nice article. Circadian rhythm has been known to man since centuries though the demonstration of its linkage with genes has been discovered recently. Healthy people have always been eating well in view of that. One golden rule that people talk about maintaining health and which I have myself experienced too well is that always eat a little bit less than you require to fill your belly completely.

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