Can eating at night give you heart disease?

Man looking in fridge late at night

New research has suggested that eating late at night can raise the risk of heart disease. We look behind the headlines.

9 November 2017

Eating at night could increase the levels of harmful fats in your blood, a study has suggested. 

The researchers, from National Autonomous University of Mexico, found that rats had higher amounts of harmful fats in their blood after they ate a meal during their natural sleeping time, compared to if they ate during their normal waking hours. 

The research

The daily rhythms of your body are driven by a tiny part of your brain known as the SCN. 

This research looked at the levels of triglycerides (a type of fat in the blood), and the role that the SCN played in this. They did this by studying rats which they fed with butter at different times of day.

They found that rats that ate at the beginning of their active period had lower levels of fat in their blood after their meal than those who ate when they would normally have been asleep. After deactivating the SCN, the rats had a similar amount of fat in their blood, regardless of whether they ate during the day or night. 

High levels of fat in the blood are known to increase the risk of heart attack and stroke, but the research did not look directly at the risk of heart attack and stroke.

It is important to note that since the study was carried out in rats, it is difficult to apply it to humans. More research is needed before we can say that the same thing happens in humans. Also, the researchers only used male rats (this is likely to be because female rats have hormone fluctuation, but this isn’t clear from the research paper).

For the 24 hours before the experiment, the rats were not allowed food and only given water. During the experiment they were fed melted butter through a tube directly to the stomach. This could have affected their normal digestion process. Similarly, humans are unlikely to consume fatty food by eating melted butter on its own, directly into their stomachs. The research didn’t look at whether eating a healthy meal at night would have any harmful effect.

Moreover, rats are nocturnal so their natural sleeping time is the opposite to humans. Their natural daytime, when they would eat, is our night-time. So we don’t know whether these findings apply directly to humans.

The rats were humanely killed after the experiment, so there is no way to know what the long-term effects on them would have been. High levels of fat in the blood are known to increase the risk of heart attack and stroke, but the research did not look directly at the risk of heart attack and stroke.

The coverage

The research was widely covered, for example in the Daily Mail, The Sun, Newsweek, and The Express.

Newsweek claims that ‘Researchers from the National Autonomous University of Mexico found that eating late goes against our biological clocks.’ This is not strictly true: the researchers found that eating late affected the levels of triglycerides in rats.

The Sun headline says: “Eating before bed raises the chance of heart disease and diabetes.” But the study didn’t look at eating before bed, and it didn’t look at diabetes

The Sun headline says: “Eating before bed raises the chance of heart disease and diabetes.” But the study didn’t look at eating before bed, and it didn’t look at diabetes. The Sun also says: ‘Shift workers, long-distance commuters, and jetlagged travellers are likely to be at risk.’ Again, this is currently unknown, and could scare readers unnecessarily.

The Daily Mail says: “Eating late at night increases the risk of heart disease and diabetes by raising levels of harmful blood fats, warns new research.” This makes it sound like the association is cause and effect, and that we can say for certain how it affects humans, neither of which are the case.

It goes on to say that “Scientists found jet lag, or simply staying up, is also dangerous by leading to midnight suppers.” The lead author of the study said that jet lag in humans could have a similar effect to eating late in rats. The rats never got to fly in aeroplanes in order to experience jet lag.

The BHF view

Maureen Talbot, Senior Cardiac Nurse at the British Heart Foundation, said: “Eating a balanced diet is essential, but this study suggests it’s not just what you eat but when you eat that’s important. Eating fatty foods, and a long-term pattern of eating late at night, may have a detrimental effect on your heart health due to increased triglyceride levels.

"Given that many people don’t work nine to five these findings may be significant, but they need to be confirmed with further research in humans. In the meantime, whether you work nights, evenings or regular office hours, we should all try to eat a healthy diet, keep active, and reduce late night snacking wherever possible.”

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