We're Getting Mealtimes Wrong - Here's the Best Time to Have Dinner

It's not only what you eat that matters – your body clock plays an important role in how you metabolise food.

"Have breakfast like a king, lunch like a prince and have dinner like a pauper," my Spanish friend and colleague Javier Hirschfeld told me when I asked about typical Spanish eating habits. It's a saying that has been drilled into him from an early age.

In Spain, it's common for lunch to be your biggest meal of the day while evening meals tend to consist of light bites. "Some people skip dinner altogether or have a piece of fruit and yoghurt," he says.

In the UK and US, it's more usual to have a light lunch followed by a bigger meal in the evening. But we may have got things backwards – that's according to an emerging scientific discipline, chrononutrition. It suggests that healthy eating is not only about what we eat, but also when we eat it.

From reducing obesity to preventing cardiovascular disease, numerous studies now show that our internal body clock, or circadian rhythm, plays a powerful role in how we process food – and our overall health. Here's why – and how to schedule your meals to capitalise on it.

Set your clock to the right 'time'

Marta Garaulet, from the University of Murcia in Spain, first became interested in the impact of meal timings after making observations in her weight-loss clinic. Over a decade ago, she observed two patients who experienced different weight-loss results, despite living together and following the exact same diet.

One had lunch around 13:00, while the other could only eat later because of her class schedule. "That was the only difference," says Garaulet. The student eating an earlier lunch had lost much more weight after six-weeks. This led her to investigate the intriguing possibility that meal timing itself could have a huge influence on weight loss.

Together with colleagues from the University of Murcia, Garaulet followed 420 adults in Spain who took part in the same weight-loss programme over 20 weeks to find that those who ate an earlier lunch lost more weight and lost it more quickly compared to those who chose to eat lunch later in the day.

Similarly, in a small randomised controlled trial, 32 healthy women ate the same meals for two weeks. Those who ate a later lunch showed poorer blood sugar control and burned fewer carbohydrates. Numerous studies have since found that our circadian rhythm influences our hunger, digestion and metabolism.

But why should eating the exact same food at a different time of day have such a powerful effect? When I asked this question to Frank Scheer, a professor of medicine and neuroscientist at Brigham and Women's Hospital in Boston, Massachusetts, he told me that it's because "we're not the same person in the morning and the evening from a biological point of view." Our internal body clock regulates almost all aspects of our physiology, he says.

That's because eating at a time when our body clock suggests it's time for sleep could create a biological mismatch called "circadian misalignment."

One example of this can be seen in how we regulate blood sugar. In a 2022 study of more than 800 adults, researchers gave each one a glucose drink designed to mimic the carbohydrate content of a typical evening meal. They found that participants processed it less efficiently when they consumed it one hour before bedtime rather than four hours earlier.

Those who drank it closer to bedtime had higher blood sugar levels and produced less insulin, the hormone that helps to regulate our blood sugar. Researchers believe melatonin, which rises as the body prepares for sleep, plays a key role in this process.

"If you eat when melatonin is elevated in the evening, your glucose control is going to be impaired," says Scheer, who was also involved with the study. The effect was even greater in people carrying a common variant of the MTNR1B gene, which has been associated with an increased risk of type 2 diabetes. Over time, later eating could therefore increase the risk of developing the condition, which has steadily been increasing worldwide.

- Author: Melissa Hogenboom, BBC

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