Are TV cookery shows making us fat?

"Is Nigella making you fat?" asks the Daily Mail, telling readers that, "TV cookery shows make us tuck into unhealthy snacks".

The headline comes from a small study that found young adults who watched a 10-minute clip of a cookery show ate more calories (around 40 more on average) from chocolate sweets than those shown a clip of a nature documentary of the same length.

Participants watched short TV clips and were then led into a room and asked to taste as much or as little as they wanted of a choice of carrots, cheese curl crisps or chocolate-covered sweets during a strict 10-minute period. Overall, the calories consumed did not differ significantly between the two groups, but those watching the cookery clip ate around 40 calories more of chocolate sweets.

The news report neglected to mention that overall calorie consumption was found to be similar. This small study was also highly artificial, with only brief exposure to the TV show (10 minutes), limited food options (three), and only 10 minutes to snack after the show, not during. This limits how relevant the study's findings are likely to be to 'real-life' TV watching. Participants were not blinded to the purpose of the study, which could also have influenced the results.

The researchers themselves acknowledge that future research should examine snacking associated with TV watching that is "more similar to real-life situations".

Where did the story come from?

The study was carried out by researchers from the Department of Psychology at Hobart and William Smith Colleges (US), and was funded by the same psychology department. The study was published in the peer-reviewed research journal Appetite.

The Daily Mail article name-drops a number of popular cookery shows alongside pictures of TV chefs Nigella Lawson and Jamie Oliver. However, they fail to mention the study's key finding that overall calorie intake did not differ significantly between the groups watching different programmes.

They instead chose to only report the finding that slightly more sugary snacks were eaten by those watching cookery shows. This was not balanced reporting of the study findings.

What kind of research was this?

This was an experimental study that aimed to examine whether watching a television cooking show affected calorie intake.

The researchers thought that if food advertisements can affect children's and adults' eating behaviours then food television programmes may have a similar impact.

They hypothesised that people would consume more calories and a greater amount of sweet foods after watching the cookery programme than those watching a non-food-based programme.

What did the research involve?

The study recruited 80 psychology students (72% female, aged 18-22 and with normal BMIs) and randomly assigned them to watch 10 minutes of a cookery show or a nature programme. They were led into a room designed to look like a kitchen that had three bowls containing pre-weighed amounts of cheese curls (crisps), chocolate-covered sweets, and carrots. The students were told that they had 10 minutes to 'taste test' the different foods and they could eat as much or as little food as they liked. They were left alone during the taste test. After 10 minutes, the researchers returned and weighed the foods again to see how much was consumed and estimated the calorie intake.

Participants attended just one session and were asked to abstain from eating for at least one hour before the study. A total of 800 calories of food was presented to each of the participants, including cheese curls (350 calories/ 70g), chocolate-covered sweets (350 calories/ 70g) and a proportionally larger weight of carrots (100 calories/ 243g).

Participants were randomly assigned to watch 10-minute clips of:

A cooking show with Rachael Ray from the Food Network channel. This clip showed a variety of different foods: prosciutto-wrapped cod, 'peasto' pasta, asparagus drizzled with balsamic vinegar, and a fruit tart for dessert.
The nature documentary Planet Earth. The clip from Planet Earth was a neutral clip that did not focus on food. It showed elephant and monkey behaviours in a jungle habitat in the Congo, and was specifically chosen to not include any footage that could intentionally cause a participant's food desire to decrease, for example watching a lion eating a zebra carcass.

The statistical analysis was appropriate and took account of pre- and post-taste testing hunger levels and desire to eat food scores, which were assessed by a questionnaire.

What were the basic results?

Across the board, participants chose to eat more calories from the chocolate sweets than the carrots or cheese curls.

After comparing calorie intake between the two groups, the researchers found:

When controlling for pre-session hunger and food desirability, there was no statistically significant difference between the two groups in terms of the total calories consumed in the taste test. Those shown Rachael Ray cookery clips ate 205.64 calories compared with 157.4 calories eaten by those watching the Planet Earth clip.
However, on average the intake of calories from chocolate-covered sweets was significantly larger for those watching cookery (103.03 calories) compared with Planet Earth (60.37). The cookery group ate approximately 40 calories more of chocolate sweets in the taste test than the Planet Earth group.
There was no significant difference between the groups in the number of calories consumed from eating the carrots or cheese curl crisps.
The groups the participants were assigned to did not affect food desirability or hunger over time.

How did the researchers interpret the results?

The researchers concluded that, "Watching food-related television programmes may affect eating behaviour, and has implications for obesity prevention and intervention efforts."

Conclusion

This small experimental study showed that participants consumed about 40 more calories from chocolate sweets after watching a 10-minute clip of a cookery show compared with those watching a 10-minute nature documentary clip. The overall calorie intake was not significantly different between the two conditions.

The study does raise the question of how much TV programmes influence our eating habits. However, it has significant limitations that should be borne in mind:

The participants only watched a 10-minute clip, which is a relatively short time to influence behaviour. Also, as most cookery shows are between 30 minutes and an hour long, the 10-minute viewing may not be particularly realistic. The effect of watching longer amounts of food-related programming was not assessed in this study and may have different effects on calorie intake.
The participants were only given 10 minutes to sample just three types of food. This highly restricted choice and artificial time limit does not mimic TV viewing and the potential snacking environment in the home. It is not clear whether the same increase in calories from sugary foods would be seen in a home environment. Here, many other factors are likely to also influence the number of calories consumed, including the availability and choice of food, and whether the person has company or not.
Participants were given extra credit towards their psychology class for volunteering to participate in the experiment. There is also no description of any attempts to hide the purpose of the experiment. Both of these aspects of study design could lead to a systematic bias in terms of eating behaviour that could favour a positive result. For instance, people who knew the aim of the study was to investigate the relation between cookery programmes and snacking may be more inclined to snack after the clip in order to fulfil their expectation that the two are linked.
It is not clear whether – or to what extent – watching food programmes on a short or regular basis influences eating habits, or whether it contributes towards weight gain or obesity. This study does not clarify this point.