Does watching TV make you fat?

http://www.theguardian.com/politics/reality-check/2013/oct/24/does-watching-tv-make-you-fat

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The UK and Poland have something in common: their citizens watch the same amount of TV - on average 242 minutes each day. But those nations pale in comparison to the US where TV worshippers average almost 5 hours according to Ofcom.

Below is a summary of those viewing habits by country as well as obesity rates around the world. We want to know if there's any correlation and, if there is a link, whether TV watching is to blame.

When you switch between the rankings for TV viewing and obesity, there's a significant reshuffle in the order of countries. And when we ran a proper statistical analysis, there was a weak connection between the two.

But that might be because we only have a few countries to compare and looking at national averages isn't necessarily the best way to understand psychological behaviour. So, is there any truth in the claim that TV expands waistlines or is this just the usual demonisation of media for all society's ills?

Cookery shows

Not all TV is the same - food-related shows might have a greater effect on our calorie intake. A couple of studies have tried to find out.

Earlier this year, researchers at the Psychology Department at Hobart and William Smith Colleges published a paper in the academic journal Appetite. Their study had 80 adults participants who "were randomized to watch a cooking or nature television program and were then presented with 800 total calories of chocolate covered candies, cheese curls, and carrots".

Even once the researchers took into account things like hunger and food preferences of the participants, they found that the individuals who had watched a food show ate "significantly more chocolate covered candies".

That might not be surprising given the rise and rise of bakery shows like the Great British Bake Off. Calories content is rarely mentioned as the slim chefs whisk their way through shows that are constant close-ups of mouthwatering plates.

Another study, this time done at the Food and Brand Lab at Cornell University looked specifically at the impact of watching food related TV on dieters ('restrained eaters' in science speak). Because dieters are more conscious of food, constantly balancing their desire for food with their desire to lose weight, the theory goes that food shows send cues that they should override their desire for control their eating habits and satisfy their desire to consume more. Their study was also published in Appetite which is hungry for this area of research.

This time, the researchers recruited 180 undergraduate students and told them they wanted to study how TV affects their taste in sweets…

The experiment group watched episodes that were food related, one where SpongeBob sold chocolate bars and the other where Jellyfish Hunter collected jelly from a jellyfish while the control group watched non-food related episodes. Participants were asked to fill out a questionnaire about their television and snacking experience and then completed a "10-item Restrained Eating Scale." We recorded the number of candies eaten during the television programs and calculated the number of calories taken in by each individual and their BMI (Body Mass Index).

The content of the episode didn't have an impact overall - but the effect depended on whether or not the participant was a dieter. For the students who were 'unrestrained eaters', regardless of their BMI, there was no difference in their eating behaviour whether they watched a food-related or non-food-related television programme.

Restrained eaters on the other hand ate more whatever the content of the programme and ate considerably more when food featured on screen (4.04 Mini Snickers and 2.35 Hillside Candies compared to 2.71 Mini Snickers and 2.05 Hillside Candies).

These studies aren't one-offs. Previous research has tried to measure the effects of eating TV and found that each hour increase in television viewing lead to an additional 167 kcal being consumed. Taken together, the research studies in this area consistently show that the idea that overweight people are lazy and therefore more likely to watch TV is misleadingly simple - cause and effect aren't a one-way street here.

So the short answer is yes, watching TV probably does increase your likelihood to consume extra calories and be overweight. But the longer answer lies in understanding the reasons why and how watching food programmes in particular can affect our behaviour in a way that watching sports programmes doesn't appear to.

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