Oregon researchers are reporting in the journal Obesity Research that they have been unable to find any basis for the conventional wisdom that late-night eating causes weight gain.

"We've all been told at one point in our lives that we should avoid late-night snacks as they will lead to weight gain," said Judy Cameron, Ph.D., a senior scientist at the Oregon Health & Science University's National Primate Research Center

"In reality, however, this belief is not based in fact," Cameron said. " We conducted a review of previous data on the topic and found no real evidence that this was true. In addition, our research in rhesus monkeys, which are considered an excellent model for studying primate (man and monkey) obesity issues, showed that eating at night is no more likely to promote weight gain than eating during the day."

The researchers reported that they studied 16 female rhesus monkeys that were placed on a high-fat diet similar in composition to the diet normally consumed by humans in the United States and other Western countries.

The researchers then observed the monkeys for one year. In addition to studying their weight gain, researchers noted how much and when the animals ate, which varied dramatically among the animals observed.

The researchers found that the monkeys ate between 6 percent and 64 percent of their total calories at night. Humans take in approximately 24 percent to 65 percent of total calories at night," the researchers said.

"We were not surprised to find that as a group, the monkeys in this study gained weight when they were placed on this very palatable diet," said researcher Elinor Sullivan. "However, what did surprise us initially was the fact that there was no clear correlation between caloric intake and weight gain. In other words, the monkeys that ate more didn't necessarily gain more weight. In addition, while some monkeys preferred to eat during the day and others ate most of their calories at night, neither of these groups gained more weight than the other."

"Overall, this research shows that caloric intake does not specifically correlate to weight gain," added Cameron. "We're now trying to determine what the cause of weight gain is."

Other sources: Obesity Research