If you enjoy your midnight snack, then I’ve got some bad news for you. Researchers found that eating at night is associated with a higher risk of heart disease and diabetes, and the body’s rhythm might be to blame.

Don’t raid the midnight fridge! Image credits: Sean Murray.

When is the right time to eat is still a matter of debate among scientists and nutritionists. Some say you should never have dinner after 7 PM. Others are a bit more flexible, but still, the bottom line seems to be that eating too late in the night is not good for you. Well, researchers at the National Autonomous University of Mexico wanted to see just what happens with the body during a midnight snack.

They fed rats right before their resting period (the equivalent of a midnight snack) and monitored the levels of fat, called triglycerides, in the blood. The levels spiked more drastically than when fed during the beginning of their active phase, indicating that the body struggled to deal with the food. The same thing didn’t really happen when the rats were fed during the day. Researchers had a hunch that this might be due to the circadian rhythm — the body’s 24h-hour cycle. In other words, the body is expecting a high influx of food during the day and is prepared to deal with it, but it’s less prepared during the night.

Scientists confirmed their theory by removing the part of the rat’s brain that controls the 24-hour cycle. After they did this, the spike disappeared; the body was expecting the food. Lead author Ruud Buijs comments on the significance of these findings (assuming they carry on to humans):

‘The fact that we can ignore our biological clock is important for survival; we can decide to sleep during the day when we are extremely tired or we run away from danger at night. However, doing this frequently – with shift work, jet lag, or staying up late at night – will harm our health in the long-term especially when we eat at times when we should sleep.’

As these fats are connected risk of heart disease and diabetes, the team also concludes that eating late increases the risk of such conditions.

So, how late is too late? There’s no clear-cut answer, as different people have different rhythms and different schedules. But Buijs says that no matter what your schedule is, you should avoid eating after 9 PM — whether you’re on a diet or not.

Journal Reference: Sofía Moran-Ramos, Natali N. Guerrero-Vargas, Rebeca Mendez-Hernandez, Maria del Carmen Basualdo, Carolina Escobar, Ruud M. Buijs. The suprachiasmatic nucleus drives day–night variations in postprandial triglyceride uptake into skeletal muscle and brown adipose tissue. DOI: 10.1113/EP086026