Tuesday October 23 2007
Eat whole-grain cereal every day
Men should “go with the grain”, reported The Times, as those who eat whole grain cereal every day reduce their risk of heart failure by almost 30 per cent. The new study adds to “existing evidence that whole-grain foods are healthy,” the newspaper said. The Daily Express suggested, “if every person in the country ate one serving of whole-grain a day, 24,000 lives a year would be saved.”
This story is based on data collected in a 20-year study of male doctors in the US. It found that an increased consumption of breakfast cereal, particularly whole-grain cereal, was associated with a reduction in heart risk. Although this study is large, there are a number of lifestyle and diet factors that contribute to the risk of heart failure, and it cannot be said for certain how much effect whole-grains are having relative to these other factors.
Where did the story come from?
Drs Luc Djoussé and J. Michael Gaziano from the Brigham and Women’s Hospital and Harvard Medical School in America carried out this research. The study was funded by the US National Cancer Institute and the National Heart Lung and Blood Institute and it was published in the peer-reviewed medical journal Archives of Internal Medicine.
What kind of scientific study was this?
This study analysed data from 21,376 male doctors, about 54 years old on average, who were enrolled in a large randomised controlled trial: the Physicians’ Health Study I. This trial randomised participants to receive low dose aspirin, beta-carotene, both of these treatments, or an inactive placebo.
Researchers assessed the men who did not have heart failure at the start of the study, and who provided information about their breakfast cereal intake and about other potential risk factors and existing medical conditions when they enrolled. Participants answered a questionnaire about how many servings of cold breakfast cereal they ate on average in the year before the study started, and what type of cereal it was. Cereals were divided into wholegrain (containing at least 25% whole grain or bran by weight) and refined cereals (less than 25% wholegrain or bran by weight). Participants also reported on their cereal consumption at 18 weeks, and two, four, six, eight and 10 years into the study. The researchers divided participants into groups according to their weekly cereal consumption.
The participants received an annual questionnaire to ask whether they had experienced heart failure or other major chronic diseases and the researchers followed participants for an average of 19.6 years. They compared the risk of heart failure between people who consumed different amounts of whole grain cereals. Analyses were adjusted for other risk factors for heart failure, including age, smoking, exercise, alcohol consumption, vegetable consumption, taking multivitamins, and the presence of existing heart problems.
What were the results of the study?
During follow up, there were 1,018 cases of heart failure. The risk of heart failure reduced with increasing cereal consumption. Men who ate two to six servings a week at the time of enrolment reduced their risk of heart failure by about 20%, and people who ate seven servings or more reduced their risk by almost 30% compared with men who ate no cereal. Similar results were found when the researchers looked at cereal consumption during follow up. When these results were analysed by the type of cereal eaten, the association was only seen with wholegrain cereals, not with refined cereals.
What interpretations did the researchers draw from these results?
The researchers concluded that eating more wholegrain breakfast cereal is associated with a reduced risk of heart failure. They suggest that more studies are needed to confirm these findings, and to look at exactly which nutrients in the wholegrains provide protection against heart failure.
What does the NHS Knowledge Service make of this study?
This is a relatively large study, but it does have some limitations.
- The people who were analysed in this study were taking part in a randomised controlled trial of aspirin and beta-carotene, it is not clear whether taking these treatments might affect heart failure risk, and this did not appear to be assessed in the analyses.
- The results in this very select group of well-educated men in the US may not apply to the population as a whole.
- The occurrences of heart failure were self-reported, and no further validation of this diagnosis was required, which may have lead to misdiagnoses. Heart failure is a complex syndrome of symptoms that are caused by the heart’s inability to maintain enough output to meets the body’s circulation requirements. The condition has multiple causes and different presentations both chronic and sudden or acute. A particular scan of the heart (an echocardiogram) is usually required to confirm the diagnosis. However, the authors report that an assessment of a subgroup of men reporting heart failure found that 90% of them did fit standard diagnostic criteria for heart failure.
- It is not clear what the researchers did when men did not return their questionnaires, or when they were reported as having died. If causes of death or non-return of questionnaires was not investigated, then some cases of heart failure might be missed.
- The questionnaires used in the study did not assess overall calorie intake or the intake of other nutrients. Therefore, it is not possible to investigate the possibility that these factors could be responsible for the association between cereal consumption and heart failure. It is also difficult when relying on self-reports of the number of servings of cereal consumed and the brand that was eaten over the past year to ensure that this is accurate data. It is unlikely that all participants would have had a stable consumption of the same quantity and type of breakfast cereal throughout the year.
- The authors themselves acknowledge that because of the relationship between cereal consumption and other lifestyle and diet choices, their results cannot say exactly how much the cereal itself is contributing to the reduction in heart failure risk.
Sir Muir Gray adds...
Cereals are good for health, and the planet, because their carbon footprint is small. Even though the study has weaknesses a whole-grain cereal-based breakfast followed by a walk to the bus stop is a good start to the day.