Thursday March 6 2008
Breakfast should be healthy
“Eating breakfast helps teenagers lose weight, a survey of eating habits in the United States has found,” said The Independent. BBC News also covered the story and reported that teens who skip breakfast weigh “on average five pounds more than those who ate first thing”. Both sources quoted the lead researchers as saying, “It may seem counter-intuitive…but while they ate more calories, they did more to burn those off.”
This is a cohort study so it cannot prove that one factor causes another, and limits conclusions that can be reached. The researchers acknowledge this and call for more studies. The study also found that the link between breakfast eating and weight change was no longer significant when weight-related concerns and disorganised eating behaviours were taken into account.
The study adds to a body evidence of an association between breakfast consumption and lower weight. Like other studies, it supports the accepted wisdom that breakfast has health benefits. The usual warnings apply though: there are known links between saturated fats and heart disease and breakfast should be a healthy meal.
Where did the story come from?
Maureen Timlin and colleagues from the Division of Epidemiology and Community Health at the University of Minnesota in Minneapolis carried out the research. It is unclear from the publication whether funding was received. The study was published in the peer-reviewed medical journal: Paediatrics.
What kind of scientific study was this?
The study was a cohort study of adolescents, where researchers were interested in establishing whether frequency of eating breakfast was related to changes in Body Mass Index (BMI) while taking into account other factors that could affect weight.
Between 1998 and 1999, the researchers enrolled 4,746 students from 31 middle and high schools in Minneapolis into the study. The participants completed an initial questionnaire when they enrolled in which they gave information on personal, behavioural and environmental factors, as well as their energy and nutrient intake (through the Youth and Adolescent Food Frequency Questionnaire) and how frequently they ate breakfast. Behaviours that might affect breakfast habits were assessed (e.g. tendency to skip meals, dieting, smoking and alcohol consumption, physical activity etc). Height and weight measurements were taken in classrooms so that BMI could be calculated.
Five years later (2003-2004), the original participants were contacted and sent a second questionnaire to assess their eating patterns and weight status. From the original 4,746 schoolchildren, 2,524 (53%) were not available (they dropped out, they had missing data or they did not complete the survey for other reasons). Pupils that completed the second questionnaire were more likely to be white females from a high socioeconomic class.
To determine whether there was a link between breakfast and weight, the researchers looked for any association between frequency of breakfast and BMI for each point in time separately and then between the two times. The second assessment (the prospective one) is the better way to assess these links and the researchers chose to assess the relationship between breakfast frequency as reported at the second survey and five-year change in BMI. They divided those who ate breakfast into three categories to compare weight change across these categories: those who ate breakfast every day, those who never ate it and those who ate it irregularly (between one and six days a week). They adjusted for different factors that may affect weight.
What were the results of the study?
The study found that the frequency of eating breakfast (daily, intermittently or never) was inversely associated with BMI. This means that people who ate breakfast more frequently had lower BMIs than those who ate breakfast intermittently or never ate breakfast, taking into account their age, gender, race, socioeconomic status, exercise and smoking and alcohol use.
This pattern was similar when the researchers took into account dietary factors (total calories, ratio of saturated and unsaturated fats, individual food items). However, the results became non-significant when weight-related concerns and disordered eating behaviours were considered.
What interpretations did the researchers draw from these results?
Though the researchers do express caution in their conclusion, they say that their findings support the importance of promoting regular breakfast eating in adolescents. They acknowledge that weight-related concerns may partly explain the association between breakfast intake and body weight change.
What does the NHS Knowledge Service make of this study?
Obesity is a complex disorder for which there is unlikely to be a single causal factor. Though this study has shown an association between eating breakfast and lower weight, it does not prove that eating breakfast will lower weight. The researchers report that “breakfast habits may be important markers of an overall healthful lifestyle pattern in youth” meaning that those who eat breakfast might otherwise have healthy behaviours (i.e. take more exercise, eat healthier foods) that are responsible for their lower BMIs. There are some limitations with this study:
- The researchers looked at the link between what adolescents are eating now and how much their weight changed since the beginning of the study. Though they did take into account what the young people were eating five years ago, it is unlikely that the participants kept to the same routine of eating breakfast for the entire five-year period.
- At the first point in time five years ago, the participants’ height and weight were taken and BMI calculated by trained research staff; however, at the second point in time, the participants reported their measurements themselves. These, and other self-reports may have had errors and therefore introduced bias to the results.
This study cannot establish cause and effeect: that eating breakfast caused the participants to have lower BMI. It adds to other evidence that it’s better to have breakfast than not, though the usual warnings apply. There is an established link between intake of saturated fats and cardiovascular disease, so breakfast should be a healthy meal.
Sir Muir Gray adds...
Interesting, but the willingness to eat breakfast may indicate other differences between those who do and those who don’t. Breakfast will reduce the need to snack.