A psychological problem with snacking in front of the telly

TV snacks are easily forgotten

Besides how hungry we feel, all sorts of other factors also affect how much we eat, including portion size and social convention. Another factor is memory for how much we've already eaten. The much-studied amnesic H.M. readily sat down to eat a second meal having just finished one, presumably because he'd forgotten he'd already eaten. Now Dolly Mittal and her team have shown that snacking while watching TV, as opposed to snacking while not watching TV, can lead us (well, women at least) to eat more later on, partly because the effect of the TV is to affect our memory for how much we snacked on earlier.

Thirty-two non-dieting women of unexceptional weight spent 20 minutes in the morning consuming as much snack food as they could, including chocolate balls, crisps and coke/orange squash. Half of them did this while watching Friends or Seinfeld, the others while sitting quietly. There was no difference in the amount of snack food the two groups consumed. Approximately an hour later, the women sat down to eat a lunch of sandwiches, biscuits, crackers and dip. The key finding is that the women who'd earlier snacked while watching TV ate significantly more of this later meal, than did the women who'd earlier snacked without TV. What's more, the TV group were also less accurate at recalling how much they snacked on in the morning. The implication seems to be that watching TV while snacking affects our memory for how much we've snacked on, thereby leading us to eat more later on.

A follow-up study was similar to the first except the researchers investigated the effects of different types of TV show - boring TV (a Lawn Bowling Contest - apologies to bowling fans), sad TV (a scene from the film Dead Poets Society), and funny TV (a Friends episode). The main finding from the first experiment was replicated as regards snacking whilst watching TV leading to more eating later on, but the specific type of TV show made no difference.

An anomaly in the results is that TV versus no TV had a larger effect on the amount eaten later on compared with its effect on recall memory. This suggests that TV has some other effect besides impairing memory for snack consumption, or else it affects memory in more ways that just impairing recall. Another issue is that the effect has so far only been demonstrated for women. When a pilot study was attempted with men, Mittal's team explained, they 'treated the experiment as an opportunity to consume as much food as possible, so the design may not be optimal for this group.'

'...[O]ur data suggest that TV probably exerts some as yet unspecified effect on participants' ability to recall earlier bouts of food consumption, leading to over-consumption on a later TV free test meal,' the researchers said. 'As TV viewing is associated with eating in so many different ways, and as overconsumption of food is a major problem in most industrialised nations, it would seem important to study exactly how this occurs.'
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Mittal, D., Stevenson, R., Oaten, M., and Miller, L. (2010). Snacking while watching TV impairs food recall and promotes food intake on a later TV free test meal. Applied Cognitive Psychology DOI: 10.1002/acp.1760