People who eat meals or snacks while watching TV, playing games or reading tend to consume more calories in a sitting, and especially later in the day, according to a UK review of two dozen past studies.
"Some studies have individually shown this before, but the evidence has never been put together," said lead author Eric Robinson from the University of Liverpool, who said the amount consumed could rise by up to 50 percent with distracted eating.
But while distracted eating can really up the calorie count, summoning up memories of what was eaten in a previous meal decreased the amount of food eaten later.
Researchers, whose findings appeared in the American Journal of Clinical Nutrition, broadly categorized eating patterns as "attentive," such as sitting quietly and recording what was eaten during a meal, or the exact opposite - "distracted." Distracted eaters do not pay close attention to food and are not as aware of how much they have eaten.
"Even though we make decisions about what and when to eat with apparent ease all the time, these decisions are actually very complex and can be easily disrupted," said Suzanne Higgs, a study co-author and psychologist at the University of Birmingham in the UK.
Robinson and his colleagues searched the scientific literature and found 24 studies conducted between 1997 and 2011 that met their main criterion of involving an experimenter who actively manipulated participants' attention, memory and awareness of eating food.
All of the studies were tightly controlled and monitored, but each had different methods of manipulating participants' attention and awareness.
For example, in one study adult men and women watched television while eating. In another, participants snacked on pistachio nuts and experimenters immediately removed the nut shells from view.
The experiments ranges in size from 14 participants to 122, and 18 of the 24 studies were done with university students as subjects. Nearly all of the men and women in the experiments were normal weight, rather than overweight or obese.
The analysis suggests statistically significant differences between participants who ate attentively and those who ate while distracted, Higgs said.
On average, eating while distracted increased the amount eaten by about 10 percent. But it also increased the amount a person ate at a later meal by more than 25 percent.
In contrast, enhancing memories of food consumed at an earlier meal reduced the amount consumed at a subsequent meal by about 10 percent. Enhancing awareness of the food being consumed at the current meal did not, however, change how people ate at that meal.
Still, in light of the overall results, the authors think that attentive eating techniques could be incorporated into weight loss regimens as an alternative to intense calorie counting, such as developing a mobile phone app that prompts people to eat with more attention and awareness.
But practices similar to attentive eating have been part of weight loss programs for decades, said Michael Lower of Drexel University, who was not involved in the study.
"The learned habits tend to dissipate after the program ends and most individuals regain the weight they lost," he said.