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Prof. David Cameron-Smith
Before you surrender to that late night craving for leftovers or a post-party burger, spare a thought for your body’s natural rhythms and what messing with them does to your health and wellbeing.
The first rays of morning sun begin an ancient cycle that connects every living thing. All animals have a 24-hour biological clock, known as a circadian rhythm, that has a powerful influence on physical activity, alertness, mood, hunger and metabolism.
And when this biological clock meets a modern 24/7 lifestyle, the human animal can suffer.
The phases of the sun trigger our sleep and wake cycle. Upon waking, a small cluster of nerves located deep in the brain, called the Suprachiasmatic Nucleus (SCN), come into play. These several thousands of nerves are located within the hypothalamus, the region of the brain that regulates many brain pathways, including those that determine when you want to eat, as well as how much and what type of food.
The SCN functions by sending out signals, firstly through the hypothalamus, then on to every other part of your body. Within each and every one of the billions of cells that make up the human body, the SCN controls the activity of a cluster of so-called CLOCK genes (technically, “Circadian Locomotor Output Cycles Kaput” – try saying that with a mouthful of cheesecake).
Named for their daily switching on and off, the CLOCK genes are master regulators of whether cells are more or less active. During the night, CLOCK genes turn down the metabolic processes of many cells. During the day, the reverse is true and cells are revved up and maximally active.
Messing with the natural sleep cycle
Just one late night or a period of disrupted sleep can unravel the synchronization of the SCN and CLOCK genes. Apart from the tiredness, there are the more subtle signs of metabolism gone haywire – blood pressure is increased, circulated levels of stress hormones rise, levels of bad fat (LDL cholesterol) are raised, and bowel habits begin to change. Inconvenient, yes, but not particularly detrimental to health.
However, multiply this to being chronically sleep deprived, jet-setting through multiple time-zones or switching work shifts, and the disturbances become more hazardous. For the estimated 20 percent of the working population who work irregular hours – either on rotating shifts, irregular schedules or night work – the health effects need to be considered.
Sleep loss and weight gain
Disconnected circadian rhythms and eating times alter the biological responses to food. During the day, the digestive tract, pancreas and metabolic tissues are primed and ready for nutrients. After eating, food is readily digested, insulin is produced and nutrients are rapidly stored and metabolised.
The exact same meal eaten out of synch results in a delayed insulin response, slowed storage, and disturbed metabolism. Because the body is not expecting to metabolise the food, it is stored. The exact same meal eaten at the wrong time is more likely to result in weight gain.
Sleep it off!
Then there are appetite hormones. Eating out of sync can be a disaster for what – and how much – you choose to eat. Late night snacks and meals tend to be higher in calories and are more likely to be convenience snacks or purchased foods. You are far less likely to be eating a piece of fruit at 2am than raiding the fridge or eating a greasy kebab. Part of the reason for this can be traced back to the hormones that are controlled by your SCN.
So the timing of when you can be the secret to helping you shed those few unwanted extra pounds. There is good scientific evidence that a late lunch and dinner make it harder to lose weight. In a published scientific study, night owls lost less weight in a carefully controlled weight loss intervention than those on normal circadian cycles.
The take out from this – aside from going easy on the take out? Try as much as possible to keep to a regular pattern of eating and sleeping.
Professor David Cameron-Smith is a regular Fit Planet contributor. A transplanted Australian living in New Zealand, he obtained a PhD in nutritional biochemistry from Deakin University, and undertook postdoctoral training at the Royal Prince Alfred Hospital, Sydney. His research interests include the importance of nutrition in the maintenance of optimal health in an ageing population, and the impact of nutrition in regulating the function of muscles.
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