A team of scientists from University of Aberdeen has found ways of controlling people’s meals to compare the impact of a large breakfast or a large dinner.

They found that people burned the same calories whenever they had their biggest meal of the day. However, appetite was noticeably smaller after big breakfasts, which could make it easier to stick to a diet.

In their investigation on the world of “chrono-nutrition” and how the food people eat is affected by the rhythms of their body’s internal clock, the researchers noted that, one idea is the “evening is a bad time to eat, because the body clock shifts our metabolism” towards sleep.

The study was carried out on 30 volunteers who all had their meals prepared for them for more than two months with breakfast, lunch and dinner adding up to about 1,700 calories a day. The volunteers spent one month having a huge breakfast using up nearly half their daily calories, followed by a smaller lunch and an even smaller evening meal.

In the subsequent month, the volunteers had their big meal in the evening rather than the morning. Their metabolism was precisely measured using doubly labelled water, which is denser than normal water and can be tracked as it leaves the body.

The results, published in the journal Cell Metabolism, found the timing of a big meal made no difference to how many calories were burned, to people’s resting metabolic rate or the amount of weight they lost. The difference was to appetite or hunger levels, which were suppressed by the large breakfast.

Prof Alexandra Johnstone, stated that it was likely to be crucial in the real world when the amount of food available was not being controlled.

“The studies suggest, for appetite control, the big breakfast was a winner. If you can start your day with a healthy big breakfast, you are more likely to maintain physical activity levels and maintain that control over appetite for the remainder of the day.”
Prof Alexandra Johnstone

Eating like a king in the morning

The breakfasts in the study included smoothies, yoghurts, eggs, sausages and mushrooms, and all contained plenty of protein which helps people feel full. It is however not clear why a bigger breakfast lowers appetite. The researchers say it is more complicated than having a full stomach in the morning and then sleeping when it is empty.

Prof Johnstone noted that there were ideas around the brain’s appetite and reward systems being “more in tune for the first meal of the day” as it breaks the overnight fast. However, the results are in contrast to most people’s eating habits.

“People are trying to maximize their sleep and don’t have time in the morning to either prepare or sit down and eat a larger meal, and therefore, by default, eat a larger evening meal.”
Prof Alexandra Johnstone

Currently, the scientists are investigating what happens when shift workers eat in the middle of the night and are also trying to establish whether people should eat according to chronotype (whether they are naturally a morning or evening person).

Dr Duane Mellor, a dietician at Aston University, explained that: “If you are thinking about changing your diet, think about times when you get hungry and may go for an extra snack”.

“If that is in the morning, then having a bigger breakfast may help. Equally if you are an evening nibbler, having a more substantial evening meal instead and eating smaller meals in the day could help.”
Dr Duane Mellor