Timed meals could prevent jetlag
Anyone who works a night shift or travels across time zones knows exactly what jetlag is. Your body wants to be awake or asleep at all the wrong times. The reason this happens is almost every cell in the body has a chemical clock ticking inside it… This is used to link the metabolism of the cell to the demands of the day. Upset that rhythm and... you know the consequences. The assemblage of clocks in the body all fall into step with a master clock in the brain. But now scientists at the University of Surrey have found that these "peripheral clocks" are also sensitive to other cues as well, like when you eat your dinner. And it might be possible to stop some of the side effects of shift work by altering when we eat. Jonathan Johnston spoke to Chris Smith about the work…
Jonathan - We now know that actually we have loads of clocks throughout our bodies. Within mammals, including humans, we have a so-called ‘master clock’ that sits at the base of the brain. This latches on to the light/dark cycle to enable our bodies to be synchronised to the lighting environment in the outside world, but we have other clocks pretty much throughout the entirety of the body. We think that these so-called ‘peripheral clocks’ that exist outside of the brain regulate local function within the tissues that they reside in.
Chris - Are they in some way linked to that master clock in the brain?
Jonathan - Yes, that’s right. In a normal situation, all the clocks in the body are in sync with one another. We know that one of the main functions of the master clock in the brain is to maintain the synchrony between all the clocks elsewhere in the body by nerve outputs, by hormonal outputs and, to some degree, by regulating behaviour as well.
Chris - So what didn’t we know?
Jonathan - What we didn’t know was how we can use things like meal timing to synchronise clocks outside of the brain. We’ve known for a while that there’s a really intimate link between circadian body clocks and metabolism. If you eat a particular meal during the daytime compared to at the nighttime, that same meal will give you much higher levels of blood sugar and blood fat after the meal if you eat the meal at night.
So we’ve known that your response to food is dependent on what time of day you eat, but we haven’t really looked in much detail at the other way round - how the time at which you eat might be able to synchronise your body clock system.
Chris - And that’s what you were doing in this paper?
Jonathan - That’s exactly what we were doing, yes.
Chris - How?
Jonathan - We used a very intensive human protocol and for the first part of the laboratory protocol we had them on fixed sleep/wake and light schedules within the laboratory. We gave them an early breakfast half an hour after they woke up, a lunch five hours after the breakfast, and then a dinner five hours after the lunch. So all their meals, if you like, were squashed toward the early part of day.
They then had another six days in the lab, and for those six days they had the same lighting and sleeping schedule as they had previously. The only difference was that each of their three meals was delayed by five hours. So they had a late breakfast, a late lunch, and a late dinner, which enabled us to then measure the effects of this late meal on their internal circadian system.
Chris - What was the pattern?
Jonathan - I think the most striking result was that the five hour delay in the mealtimes caused a five hour delay in our natural rhythms of blood sugar concentration. So clearly, our mechanisms for controlling blood sugar were able to be re-synchronised with food.
Chris - Why does that matter?
Jonathan - Because we know that a lot of people experience elements of what we call circadian desynchrony.
Chris - So jetlag?
Jonathan - Jetlag is a classic example. Another one would be people doing shiftwork. People for a number of years now have been looking at how we can use things such as light or a melatonin tablet to try and resynchronise these rhythms. The problem there is that we know that light and melatonin are very effective, if given at the right time of day, in resynchronising the master clock within the brain but they probably don’t have much direct effect on our metabolic rhythms.
So what this means now is that we know shift workers have a high association with things like obesity, metabolic disease, and cardiovascular disease. What we hope in the future is that if we can incorporate timed meals as a strategy for helping these people, that will then reduce some of their long term risk factors for these very important diseases.