Lis­ten to tick­ing cir­ca­dian clocks to stay healthy

The new peas­ant cook­ing means hav­ing a light din­ner – and a right royal break­fast

The Irish Times - Tuesday - Health - - Health Food - John McKenna John McKenna is edi­tor at

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 chrono-nu­tri­tion. Your mother also has a name for the dis­ci­pline: she calls it break­fast.

Chrono-nu­tri­tion 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.

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 chrono-nu­tri­tion 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.

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

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