Fast food

Wednesday October 22 2008

“Bolting down food helps to treble the risk of being overweight,” The Independent reports. A Japanese study has found that “a combination of eating quickly and eating until full can really pile on the pounds”, the newspaper says. The study found that about 60% of women and 50% of men ate until they were full, and just under 40% of women and 50% of men “confessed to eating in a hurry”. People who had both of these eating habits had higher total calorie intakes and higher BMIs, and were three times more likely to be overweight than those who did not.

This study found a link between eating habits and weight at one point in time only; it is not possible to say whether these eating habits caused the differences in weight seen. If people are overweight, the ideal way to lose weight is by both reducing their calorie intake and increasing their physical activity. If eating less quickly and stopping eating before they are full helps some people to do this, then they should use these techniques.

Where did the story come from?

Dr Koutatsu Murayama and colleagues from Osaka University and other universities and research centres in Japan and the US carried out this research. The study was partly funded by the Japanese Ministry of Education. It was published in the peer-reviewed British Medical Journal.

What kind of scientific study was this?

This was a cross-sectional study looking at the relationship between being overweight and eating until full and eating quickly.

The researchers sent questionnaires about diet to 4,140 people aged 30 to 69 years old from two communities in Japan, one rural and one suburban. Researchers excluded people who had a history of cardiovascular disease, who had a very high or very low daily energy intake (over 4,000 kilocalories or under 500 kilocalories), or who did not provide information on speed of eating or eating until full.

In all, 3,287 people (79%) returned their questionnaires and met the inclusion criteria. The diet questionnaire asked about eating habits in the previous month, and included questions about whether people usually ate until full, and how fast they ate (very slow, slow, medium, fast, very fast). People who reported eating very fast or fast were classed as eating quickly. The researchers tested the questionnaire’s validity as a measure of eating speed by comparing participants’ answers about speed of eating with their speed of eating as reported by a friend. After a year, researchers also repeated the questionnaire in a subgroup of participants, to see if they gave the same answers.

The researchers measured participants’ height and weight in a standard way, and they calculated each person’s body mass index (BMI). A person with a BMI of 25 or over was considered overweight. The participants were also asked about their occupation, how often they exercised, whether they smoked and, if so, how many cigarettes.

The researchers then looked at whether people who ate until full or ate quickly were more likely to be overweight, and whether any combination of these factors produced a greater effect on weight than might be expected from their individual effects. The researchers took into account factors that could affect results, such as where individuals lived, their occupation, age, smoking, exercise habits, total energy intake, amount of fibre in their diet and their alcohol intake.

What were the results of the study?

Among the participants, 56% reported eating until full, and 32% reported eating quickly. Just over a quarter (26%) of participants were overweight. People who ate until full and ate quickly had higher total energy intakes and BMIs than those who had neither of these habits. For example, men with both habits had an average total energy intake of 2,296 kilocalories compared with 2,190 kilocalories in those who did not, and their BMIs were 25 compared with 23 respectively.

Men or women who ate until full were about twice as likely to be overweight as those who did not (odds ratio [OR] for being overweight: 2.0 for men, and 1.9 for women; 95% confidence intervals 1.5 to 2.6 and 1.5 to 2.4, respectively). There were similar increases in risk in people who ate quickly compared with those who did not (OR for being overweight: 1.8 for men, and 2.1 for women; 95% confidence intervals 1.4 to 2.4 and 1.7 to 2.6, respectively).

People who ate until full and ate quickly were about three times more likely to be overweight than those who did not have either of these characteristics (OR for being overweight: 3.1 for men, and 3.2 for women; 95% confidence intervals 2.2 to 4.5 and 2.4 to 4.3, respectively).

What interpretations did the researchers draw from these results?

The researchers concluded that “eating until full and eating quickly are associated with being overweight in Japanese men and women, and these eating behaviours combined may have a substantial impact on being overweight”.

What does the NHS Knowledge Service make of this study?

This study shows that people who eat quickly and until full are more likely to be overweight. However, there are some limitations to consider:

  • Because a study of this design cannot establish whether these eating behaviours started before a person became overweight or obese, it cannot prove that these eating behaviours caused people to be overweight.
  • Dietary habits and eating patterns may be quite different in Japan from other countries, and therefore the study results may have limited applicability elsewhere.
  • Eating habits were self-reported, and measures would be relatively subjective. For example, what one person considers to be eating quickly may not be the same for another person, and the same applies to perceptions about eating until full.
  • A person’s perception of their own eating habits (as well as external perceptions of another’s eating habits) may be affected by their weight. For example, people who are overweight may assume that they must have negative eating habits (eating too quickly or overeating). This could affect the results of this type of study.

If people are overweight, the ideal way to lose weight is both by reducing their calorie intake and increasing their physical activity. If eating less quickly and stopping eating before they are full helps some people to do this, then they should use these techniques.

Sir Muir Gray adds...

My mother always said, "chew your food 32 times before you swallow" and she was usually right.

Analysis by Bazian
Edited by NHS Choices