Thursday January 8 2015
The Nordic diet is rich in fish and wholegrain products
"A Nordic diet could reduce the dangers of being overweight, a study suggests," The Daily Telegraph reports. The headline comes from the results of a small randomised controlled trial.
Half the people in the trial were put on the Nordic diet, which consists of wholegrain products, vegetables, root vegetables, berries, fruit, low-fat dairy products, rapeseed oil, and three servings of fish a week.
The other half acted as a control group and ate a diet of low-fibre grain products, butter-based spreads, and a limited intake of fish.
Researchers found people on the Nordic diet developed reduced activity (expression) in 128 genes associated with inflammation of their abdominal fat compared with controls.
Inflammation may cause some of the adverse health effects associated with being overweight, such as insulin resistance, which is a risk factor for type 2 diabetes.
However, changes in gene expression are not the same as proven changes in clinical outcomes. The study did not find any correlation between these changes in gene expression and clinical measurements of risk factors, such as blood pressure or cholesterol.
Nevertheless, it is plausible that the Nordic diet has a protective effect – it is relatively similar to the Mediterranean diet (with a bit more herring and a bit less pasta), which has been associated with a reduced risk of chronic diseases.
Where did the story come from?
The study was carried out by researchers from a number of academic institutions in Finland, Norway, Sweden, Iceland and Denmark.
Funding came from several sources in these countries, including research foundations and academic institutes. Several commercial companies provided food products for the study participants.
The study was published in the peer-reviewed American Journal of Clinical Nutrition.
The Daily Telegraph and the Mail Online's coverage was accurate, but both overstated the results of the study, failing to point out that research into gene activity alone is not enough to show the health benefits of a diet.
What kind of research was this?
This was a randomised controlled trial, which is the best way to determine the effects of an intervention.
The trial was designed to look at whether a Nordic diet had an effect on the activity of genes in abdominal fat just beneath the skin (adipose tissue) in obese people.
It also aimed to see whether any changes in gene expression were associated with clinical and biochemical effects.
In previous research, "dysfunctional adipose tissue" had been proposed as an important link between obesity and its adverse health effects, such as insulin resistance and an unhealthy balance of blood fats.
However, little is known about how diet influences adipose tissue inflammation at the molecular level.
What did the research involve?
Researchers recruited 200 adults to the trial, although only 166 completed it. Participants had to be between the ages of 30 and 65, with a body mass index (BMI) of 27 to 38. A BMI of 25 or above is considered overweight, while a BMI of 30 or above is considered obese.
Participants also had to have at least two other features of metabolic syndrome, a condition characterised by symptoms such as high blood pressure, high blood sugar and abnormal blood fat levels, and is often associated with diabetes.
For a period of 18 to 24 weeks, 104 people were put on the Nordic diet, comprising wholegrain products, berries, fruits and vegetables, rapeseed oil, three fish meals a week, and low-fat dairy products. They also avoided sugar-sweetened products.
96 people were put on the control diet, comprising low-fibre cereal products and dairy fat-based spreads, with a limited amount of fish.
A clinical nutritionist or a dietitian gave instructions about the diets. The participants' dietary intake was monitored throughout using regular food records.
To reduce any confounding factors, the study participants were advised to keep their body weight and physical activity unchanged, and to continue their current smoking habits, alcohol consumption and drug treatment during the study.
Researchers took biopsy samples of the participants' adipose tissue at the beginning and end of the study, and extracted RNA, which is used to carry out DNA's genetic instructions.
A test called a transcription analysis was performed to study the expression of genes in the tissue.
Researchers also took various other clinical and biochemical measurements, including levels of blood sugar, cholesterol and triglycerides.
What were the basic results?
56 participants were included in the final analysis – 31 from the Nordic diet group and 25 from the control group.
People were excluded if there was a change in their body weight of more than 4kg, and if they started to use statins, had a BMI over 38, or poor adipose tissue samples.
The researchers report differences between the two groups in the activity of 128 genes.
Many of these genes were associated with pathways relating to the immune response, with a slightly reduced activity among people in the Nordic diet group and increased activity among people in the control diet group.
There were no differences between the groups in terms of clinical or biochemical measurements.
How did the researchers interpret the results?
The researchers say their study indicates that the Nordic diet reduced the activity of genes associated with inflammation in adipose tissue when compared with the control diet group.
The quality of diet may be an important factor for regulating adipose tissue inflammation independent of weight change, they say.
This study found that the activity of certain genes, some of which are associated with inflammation, was different in obese people who ate a Nordic diet compared to those on a control diet.
Yet there was little correlation between these findings and any changes in measurements of risk factors such as participants' cholesterol or blood pressure. The authors concede that the clinical relevance of their findings is unclear.
As the authors say, one limitation is that volunteers in the study may have had healthy eating habits before the study began.
If these volunteers had been randomised to the control diet group, they may have modified their diet to become more unhealthy, and therefore changes in gene expression would seem to be more evident in this group.
Being overweight or obese increases the risk of chronic illness such as diabetes, heart disease and some cancers, so it's important to maintain a healthy weight.
The Nordic diet is being touted as one of the latest trends in healthy eating. Whether it is a proven method to prevent chronic diseases is uncertain, but it does appear to be based on sensible nutritional principles, such as eating lots of wholegrains, fruit and vegetables, while cutting down on saturated fats.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.