Why late night dining may encourage weight gain

Eating after the sun has gone down might trigger weight gain, say researchers who have been studying the effect in mice.

Even when given the same amount of calories overall, mice that ate around the clock put on more fat.

Fasting for at least 12 hours appears to switch on important fat burning pathways in the body.

The US team told the journal Cell Metabolism they now plan human tests to see if the same is true in man.

During the study around 400 mice were fed diets high in sugar or fat or both, or normal diets and over different time periods.

Overall, mice that were only allowed to feed for nine or 12 hours gained less weight than mice that could eat the same amount food but at any time they wanted in a 24-hour period.

Even when the restricted feed time mice were allowed a blow out at weekends and could eat when they liked, they still gained less weight, suggesting that the diet can withstand some temporary interruptions, the researchers said.

And when obese mice who had been eating freely were moved to a restricted schedule they lost 5% of their body weight even though they were eating the same number of calories as before.

The researchers believe a key to controlling weight gain could be sticking to a consistent 12-hour fast every 24 hours.

In the experiments, fasting at night had beneficial effects on blood sugar and cholesterol and reversed the effects of diabetes in the mice.

Study leader Dr Satchidananda Panda, an associate professor at the Salk Institute in California, said that brown fat, which burns energy at a much higher rate is also activated by this approach.

Additional work in mice by another team showed that limiting eating to half the day also altered the balance of microbes in the gut, which experts say might be important.

Dr Perry Barrett, a senior research fellow at the University of Aberdeen who does research on regulation of appetite said: "The revelation that there is a circadian rhythm in gut microbes now adds another dimension to this very interesting area of research."

He said there had not been many human studies in this fairly new area of 'chrono-nutrition' but those that had been done had so far concentrated on sleep cycles.