To stay alert during night shifts, it is best to avoid meals with sugars that are digested quickly. Photo Shutterstock People who work night shifts or rotating shifts deviate from the traditional cycle of sleep and wakefulness. This disrupts their internal biological clock, with negative consequences for their health. PhD candidate Perdana Suyoto (Human Nutrition and Health) investigated whether and how nutrition can protect against these disruptive effects.
The human body has an internal biological clock that is set to a 24-hour cycle. Biological processes – such as your glucose metabolism – work faster during the day and slower at night when you are supposed to be sleeping.
If this biological clock, known as the circadian rhythm, is disrupted for a long period of time – for example, by night shifts – the risk of obesity, type 2 diabetes and cardiovascular disease increases. That is because the body has to work harder to maintain blood sugar levels after meals eaten at times that are unusual for the biological clock. The right diet can help limit these health risks. Suyoto: ‘It’s not just about what you eat, but also how much and when.’
Nurses
Suyoto studied female nurses working night shifts at a hospital. He had them eat zero, one or three meals with a high or low glycaemic index, i.e. containing food with sugars that are digested quickly or slowly respectively. For example potatoes, white bread and cornflakes contain sugars that are digested quickly, while dairy products, pulses and fruit contain sugars that are digested slowly. ‘Meals with a high glycaemic index caused significant blood sugar fluctuations, regardless of the number of meals. We saw this not only during the night shift itself, but also the following morning.’ If the meal had a low glycaemic index, these fluctuations disappeared. ‘This shows that the type of meal is more important than the frequency. Meals with a low glycaemic index are a good alternative to fasting during night shifts.’
Suyoto also discovered that these blood sugar fluctuations reduced sustained alertness. ‘These results show that it is important to avoid high blood sugar spikes in order to stay alert. So it’s better to avoid meals with a high glycaemic index during night shifts.’
Social jet lag
Even people who don’t work night shifts can have a disrupted biological clock, as it can become disrupted simply when bedtimes change. This happens, for instance, with social jet lag: when a person’s social obligations don’t match their natural rhythm. Social jet lag is the difference between hours spent asleep during the week and at weekends. ‘That is the case for night owls who have to get up early for college or work, for example,’ explains Suyoto. ‘The greater the difference between hours spent asleep and awake on workdays and days off, the greater the social jet lag.’
High social jet lag – a difference of two hours or more – increases the risk of type 2 diabetes by 45 per cent. Suyoto found that this is partly related to diet. ‘People with high social jet lag eat less healthily: they consume more alcohol, sugary drinks and processed foods. Their higher fat and sugar intake increases the risk of diabetes, while plant-based proteins actually provide protection.’
Disruptions to the circadian rhythm lead to an impaired glucose metabolism and increase the risk of type 2 diabetes. ‘The hopeful news is that with the right nutrition, you can help control the blood sugar fluctuations that arise from circadian rhythm disruptions.’
