Tuesday January 6 2015
Wholegrains can help lower cholesterol
"The key to a long and healthy life? A bowl of porridge every day," is the somewhat inaccurate headline in the Daily Mail.
The study it reports on was looking at the health benefits of wholegrains in general, not just porridge.
These headlines are based on a study of more than 110,000 men and women in the US, who were followed up from the 1980s to 2010.
Their diets were assessed every two to four years, and the researchers looked at whether the quantity of wholegrains people ate was related to their likelihood of dying during follow-up.
Fans of wholegrains, which include brown rice and oats, claim they can improve digestion, reduce cholesterol levels and make people feel fuller so they are less likely to snack.
The researchers found people who ate the most wholegrains were about 9% less likely to die during follow-up, and about 15% less likely to die from heart disease specifically, compared with people who ate the least.
We know that people who eat wholegrains also tend to have healthier lifestyles, so researchers tried to take this into account. But, as the authors acknowledge, it is impossible to be certain that other factors aren't contributing.
With that limitation in mind, this is a good-quality study, which supports the benefits of eating more wholegrain foods.
Where did the story come from?
This research was carried out by researchers at the Harvard School of Public Health and other research centres in the US and Singapore.
It was funded by the US National Institutes of Health and the National Heart, Lung, and Blood Institute.
It was published in the peer-reviewed Journal of the American Medical Association (JAMA) Internal Medicine.
While the general content of the stories that appeared in the Daily Mail and The Daily Telegraph was accurate, the headline writers developed a strange obsession with porridge.
While porridge can be a good source of wholegrains, the foodstuff was never actually mentioned in the study. All dietary sources of wholegrains were added together for the analyses, so the study did not show whether one source was better than another.
What kind of research was this?
This was an analysis of data from two prospective cohort studies looking at whether eating more wholegrains is associated with living longer.
The researchers note wholegrains have been found to be associated with a reduced risk of diseases such as type 2 diabetes and heart disease.
But while some studies have suggested they are associated with living longer, others have not. The researchers wanted to use a large, good-quality study to assess this question.
This type of study is the best way to assess this question, as it would not be feasible to do a randomised controlled trial where people's diets were controlled over a long period of time.
Collecting data prospectively gives the best chance of getting complete and correct information about people's exposures (such as what they ate) and their outcomes during follow-up (such as whether they died).
As with all studies of this type, people who eat more wholegrains may also have other healthier behaviours or characteristics, such as taking regular exercise, which could affect their risk of death during follow-up.
To try to remove the effect of these other factors (called confounders), researchers need to measure them and take them into account in their analyses.
What did the researchers do?
The researchers collected detailed information on the diets and other characteristics of 118,085 adults. They followed them for up to 26 years to find out who died.
They then looked at whether people who ate more wholegrains were less likely to die in this period than those who ate fewer wholegrains.
The researchers analysed data collected in two US studies called the Nurses' Health Study (all-female participants) and the Health Professionals Follow-Up Study (all-male participants) between the 1980s and 2010.
They only included people who did not have heart disease or cancer at the start of the study, and those who had completed full questionnaires on their diets.
The studies collected information on participants' diets using accepted food frequency questionnaires every two to four years.
These questionnaires asked about how often the individual had eaten specified portions of a wide range of foods in the past year.
The researchers used the information collected to estimate each person's wholegrain intake from grain-containing foods such as pasta, rice, bread and breakfast cereal.
The following foods were considered wholegrains:
- whole wheat and whole wheat flour
- whole oats and whole oat flour
- whole cornmeal and whole corn flour
- whole rye and whole rye flour
- whole barley
- bulgur wheat
- brown rice and brown rice flour
- amaranth and psyllium (two other types of grains)
This included wholegrains that were intact (such as brown rice) and those where the grain had been broken down, but the food still retained all of the contents of the wholegrain (such as whole wheat flour). The questionnaire also asked how much added bran or wheat germ a person ate.
The researchers identified people who had died through the US National Death Index, the postal service, or through relatives of the participants. They used death certificates to identify the cause of death in each case.
The researchers then analysed whether those people who ate more wholegrains on average were less likely to die during follow-up.
This involved dividing people into five groups according to how many wholegrains they ate, and then comparing the proportion of people who died in each group.
In their analyses, they took into account a wide range of factors that could influence results, such as:
- total calorie intake
- body mass index (BMI)
- physical activity
- taking multivitamins
- taking aspirin
- family history of heart disease, cancer or diabetes
- medical conditions such as high blood pressure, diabetes or high cholesterol
- overall healthiness of the diet (using a score based on intake of 10 foods and nutrients linked with a higher or lower risk of chronic diseases, such as red or processed meat and fruit and vegetables)
They also discounted any dietary information collected after a person developed diabetes or heart disease, or had a stroke, as this led to these people changing their diets as a result. They looked at total deaths overall, as well as deaths specifically from heart disease and cancer.
What were the results of the study?
Women with the lowest intake of wholegrains ate about four grams of wholegrains per day on average, and this figure was about six grams per day for men.
Women with the highest intake of wholegrains ate about 36 grams per day on average, and this figure was about 53 grams per day for men.
Men and women with higher wholegrain intake also tended to be more physically active, less likely to be current smokers, have lower alcohol intake, and eat healthier diets overall. They were also more likely to have had a high cholesterol level at the beginning of the study.
On average, participants were in their 50s when the study started. In total, the researchers collected more than 2.7 million years of follow-up (the sum of the number of years each person was followed up for). During this time, 26,920 of 118,085 participants (about a quarter) died.
After taking into account potential confounders, the researchers found a significant trend for reduced risk of death during follow-up with increasing wholegrain consumption.
People who had the highest wholegrain consumption were 9% less likely to die during follow-up than those with the lowest wholegrain consumption (hazard ratio [HR] 0.91, 95% confidence interval [CI] 0.88 to 0.95).
When looking at death from specific causes, people who had the highest wholegrain consumption were 15% less likely to die from heart disease during follow-up than those with the lowest consumption (HR 0.85, 95% [CI] 0.78 to 0.92). Wholegrain consumption was not linked to risk of death from cancer.
The researchers estimated each additional 28 gram serving of wholegrains per day was associated with a 5% reduction in overall risk of death during follow-up (HR 0.95, 95% CI 0.93 to 0.98) and a 9% reduction in the risk of death from heart disease (HR 0.91, 95% CI 0.87 to 0.96).
How did the researchers interpret the results?
The researchers concluded that eating more wholegrains is associated with a reduced risk of death during follow-up, and of death from heart disease specifically, in women and men in the US.
This link remained even after taking other lifestyle factors into account. They say their findings support recommendations to increase wholegrain intake to reduce the risk of chronic diseases.
This analysis of two large prospective cohort studies from the US has found an association between higher wholegrain intake and a reduced risk of death during follow-up, particularly from heart disease.
The study benefits from its large size (more than 100,000 participants) and long duration, as well as the thorough collection of information on the participants as the study progressed (prospective data collection).
Our diets and lifestyles are very complex, and it is very difficult to entirely isolate the effect of one dietary component and remove the effect of all other factors.
However, the researchers have assessed and taken into account a wide range of factors in their analyses that could affect the risk of death. This means the results are more likely to reflect the effect of wholegrain foods specifically, rather than other factors.
But the authors themselves acknowledge some factors may still be having an effect. In addition, the study relies on self-reported estimates of dietary intake from the participants, which may not be entirely accurate.
All of the participants in the study were health professionals from the US. The results may not be representative of what would be seen in other groups – for example, those of lower socioeconomic status.
Also, while the study found no reduction in deaths from cancer overall, it did not look at deaths from individual types of cancer, such as bowel cancer.
With these limitations in mind, the researchers have produced a large, useful and good-quality study. The findings reinforce the benefits of including more wholegrains in our diet.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.