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The connection between diet and health

Understanding the role of diet on health

Food and drink play a large part in peoples day to day lives, and it is well understood by researchers that what we choose to eat and how frequently has an impact on our long term health. There are many bold claims made within the press and conflicting messages around whether certain foods are ultimately good or bad. 

In this article, Dr Richard Berks investigates the positive impact the UK Biobank repeat diet questionnaire is having on our understanding of the role of diet on health. Combined with the detailed genetic, imaging, and biomarker data in UK Biobank, it is enabling scientists to ask new, imaginative questions around diet and its impact on long term disease.

The collection of diet information in UK Biobank

To understand the link between people’s health and what they eat and drink, you first need to collect information about their diet. This is done in two ways in the UK Biobank study. Firstly, participants are asked to fill out a questionnaire on a touch screen at recruitment and at imaging centres, about how often during an average week they consume certain foods or drinks.

The second is an online questionnaire sent by email, where the participants are asked exactly what they consumed in the day before – known as a ‘24-hour recall’ dietary questionnaire, or the Oxford WebQ.

Dr Aurora Pérez-Cornago from the University of Oxford, an expert in studying the effects of diet on health, explains the pros and cons of these two different questionnaires.

The benefit of the 24-hour diet recall questionnaire

Apart from it being relatively easy to complete – is that it’s very detailed, asking about over 250 different food and drinks. But it’s a person’s long-term diet, what you usually eat and drink, that is of most value to research. When participants complete the 24-hour recall questionnaire over and over, so you can estimate a person’s long-term diet. That’s why UK Biobank participants have been asked to complete this 24-hour questionnaire on several occasions.

Dr Aurora Pérez-Cornago, University of Oxford

Clearing up diet controversies

The connection between diet and health is never far away from the headlines. One thing that people tend to take away from the latest news stories is a lot of conflicting advice.

“A lot of what we hear in the news is a result of people just taking one study and suggesting it gives the definitive answer, when it doesn’t – and that’s what can lead to conflicting messages,” Aurora explains. “I see it all the time in my family and friends – they’re trying to look for that one ‘superfood’ that will be the key to their good health. But it doesn’t exist. What usually matters is our whole diet and our overall lifestyle, not one specific food.”

One example of a diet-related controversy is coffee and heart disease. A recent news story, which came out of research using UK Biobank data, said that six or more coffees a day can be bad for your health. But only a few weeks earlier, the message that grabbed the headlines is that drinking 25 cups of coffee in a day is fine. Clearly these two messages can’t both be true – so how does this kind of situation occur?

Prof Jeremy Pearson, Associate Medical Director for the charity British Heart Foundation, explains that the conflicting messages arise because of the different ways that scientists study diet.

There were a few drawbacks in the ‘25 cups of coffee’ story which British Heart Foundation picked out – influenced by how the research was carried out.

The benefit of long term follow up

In my view, one of the reasons why studies disagree with each other is because quite a lot of these diet studies are not good quality. For example, they’re often very small studies, doing something quite extreme for quite a short time, in very controlled conditions. Then the results are extrapolated to try and apply it to all people. It’s not easy to draw the right conclusions from studies like that. UK Biobank are monitoring diet and other things over a long time, and correlating these with what actually happens to people’s health. This will probably result in findings that are more reliable than any short-term study.

Prof Jeremy Pearson, Associate Medical Director for the charity British Heart Foundation

UK Biobank is helping diet research

UK Biobank is contributing to research looking at diet across all areas of health.

For example, Prof Alex MacGregor from the University of East Anglia is studying the role of diet in arthritis. He’ll be studying three specific types of diet – ‘Mediterranean’ style diets, diets high in fruit and vegetables, and diets low in fat – which people have claimed in the past might be able to prevent or control arthritis. By studying the UK Biobank cohort, he will be able to assess the evidence behind these claims.

Dr Claire McEvoy from Queen’s University Belfast is studying how diet and obesity might affect the brain and influence the development of dementia later in life. She will be studying the connection between the things we eat, and measures like the amount of grey and white matter in the brain, as well as cognitive abilities. She hopes to be able to find changes in their diet which could help certain people avoid dementia later in life.

The value of UK Biobank

Of course, data on diet is only one part of what participants in UK Biobank are asked to contribute. “For me, the value of UK Biobank is that it’s not only looking at diet, it’s looking at lots of different things,” Aurora explains. “Combining the diet information with things like the genetic data, biomarkers in the blood, and the imaging part of the study – that’s what makes UK Biobank a really unique resource.”

Investigating the effect of our diet on our health is clearly a challenging task, and there’s no doubt that conflicting messages around food and drink will continue to arise. But UK Biobank and studies like it are providing researchers with the data they need to ensure diet advice is as accurate and helpful as possible.

Jeremy believes that a large part of what scientists will get from UK Biobank’s diet data will probably confirm what we already know. “That will give us more certainty that the existing recommendations when it comes to diet are correct”, he says.

“But what I think is perhaps more interesting is that we may find something completely new – because the size and scope of the UK Biobank study makes it more powerful. Imagine if, by combining the genetic data and the dietary data, it might be possible to find a genetic variant which makes certain people more susceptible to the effects of salt, for example.

“I suspect that UK Biobank and studies like it will tell us the answers to the questions we have – but also reveal entirely new things we never even dreamt of finding.”

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