The ideal diet: eat a small dinner, but a big breakfast

We all know that you are what you eat. The thing is, that's only the half of it. Increasingly, we are coming to realise that when you eat is also vitally important to your good health.Welcome to what the scientists call chrononutrition. Your mother also has a name for the discipline: she calls it breakfast.

Chrononutrition is important because of our circadian cycle. The circadian cycle has been around a whole lot longer than we have. "Infusing all life going back nearly four billion years, is the circadian cycle, the time of days," writes Alan Burdick in his book Why Time Flies.

Burdick points out that “virtually every cell in the human body contains a circadian clock of its own”. Just think about that: you are actually a collection of billions upon billions of little clocks, all working together.

The fascinating thing about the circadian cycle is that it is almost, but not quite, equal to our well-understood 24-hour clock of the day: the circadian clock is 24.2 hours: circa diem, about a day.

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We use daylight to reset our circadian clock and to keep it controlling how we function: our heartbeat; our blood pressure; how much alcohol we can drink – you metabolise booze more slowly between 10 at night and 8 in the morning, which is why that late drink has more impact.

The circadian clock controls our body temperature, our alertness – shift workers call the hours before dawn the “zombie zone”, because that’s when you are most likely to make an error – and even influences the time of day are born – about 4am – and when you die (an hour later, usually).

"Our biological clock instils a personal rhythm in each of us . . . genes determine the course of our body clocks," writes Stefan Klein in Time: A User's Guide.

Research in the field of chrononutrition has already unearthed a delicious irony: when Maimonides wrote, back in the 12th century, that one should “Eat like a king in the morning, a prince at noon, and a peasant at dinner”, he not only revealed that he understood circadian rhythms, he revealed one of the most important aspects of food and health.

Your metabolic markers will show an improvement if you have a big breakfast and a small dinner. Eating late at night disturbs our sleep, and increases the risk of diabetes and obesity. If you are crossing a time zone in an aeroplane flight, don’t keep eating the food they give you, as your circadian clock will go out of kilter, making the jet lag even worse.

In one study, volunteers were trained to live on an 28-hour day, which inverted their normal eating times. Within 10 days, their blood pressure had rocketed, their blood sugar levels went above normal, and two of the 10 volunteers were classified as prediabetic, all because they were eating when their bodies weren’t primed to metabolise the food.

In modern society, very many people work – and therefore eat – at unusual hours. As a consequence, they suffer what is known as “social jet lag”, with attendant risks for obesity, heart disease and diabetes. So, we need to eat when we are hungry, at consistent mealtimes, and we need to listen to the ticking of those billions of circadian clocks that keep us healthy.

And the new peasant cooking means having a light dinner. And a regal breakfast.

John McKenna is editor at guides.ie