Urine test could reveal if your diet is a threat to your health

"A urine test that can reveal how healthy your meals are has been developed by UK scientists," BBC News reports.

Researchers wanted to see if they could help crack one of the biggest problems confronting people trying to carry out studies into diet and health. Namely, that the most widely used method to assess diet – self-reporting – is notoriously unreliable.

Study after study has found that most people are prone to under-reporting the amount of unhealthy food they eat while over-reporting the amount of healthy food.

In this small study, on four separate occasions, 20 participants consumed four different diets which were assessed as ranging from very healthy (in terms of agreeing with international guidelines) to unhealthy.

Urine samples were tested for substances known to be associated with certain types of dietary patterns (metabolic profiles).

The researchers found that urine tests were in fact robust enough to identify dietary patterns in the participants – the levels of 19 substances (metabolites) were significantly higher in the healthiest of the four diets compared with the unhealthiest.

As this study had a very small sample size, it's likely that more research will be needed to verify the findings, before considering how best urine tests could be adopted as a dietary tool for health services.

If you are looking to make your diet more healthy, you may want to start keeping a food diary – where you record exactly what you eat, rather than relying on your unreliable memory.

Where did the story come from?

The study was carried out by researchers from a range of institutions in the UK, US and Denmark including Imperial College London, Northwestern University and the University of Southern Denmark.

It was funded by the UK National Institute for Health Research and the UK Medical Research Council. Some of the researchers have received payments the large food and consumer goods manufactures Unilever and Nestlé.

The study was published in the peer-reviewed scientific journal Lancet Diabetes and Endocrinology. It is available on an open-access basis so is free to read online.

Both BBC News and the Mail Online's reporting of the study was accurate.

What kind of research was this?

This was a randomised-controlled crossover trial which wanted to investigate whether dietary intake in individuals could be revealed and measured using urine samples.

Diet has a part to play in the increase in risk of non-communicable (non-infectious) diseases such as type 2 diabetes and heart disease. Current dietary tools aren't always able to assess the effect of policy change on dietary behaviour in populations. The researchers wanted to see if urine metabolic profiles could reflect dietary intake and offered an alternative method to do this.

Randomised trials are one of the best ways to determine the effects of an intervention. Crossover trials are when participants act as their own control and receive the different tested interventions in random order, in this case the different diets. They are often used when the sample size is small – as was the case with this trial – as a way to boost the numbers for comparison.

In this study, it wasn't possible to blind the participants from the dietary intervention but the individuals analysing the data were prevented from knowing the randomisation order.

What did the research involve?

Between August 2013 and May 2014, healthy volunteers (aged 21-65) with a body mass index (BMI) between 20–35kg/m2 were recruited for this study from a database at the UK National Institute for Health Research (NIHR)/ Wellcome Trust Imperial Clinical Research Facility (CRF).

Of a potential 300 recruited by invitation letter, only 26 were eligible and attended a health screening, 20 of these people were randomised in the trial.

The trial aimed to assess four dietary patterns which varied in a stepwise manner in their compliance with World Health Organization (WHO) healthy eating guidelines. Essentially the diets gradually increased in content of fruits, vegetables, whole grains, and dietary fibre, while decreasing in their content of fats, sugars, and salt.

Participants were asked to attend four inpatient stays of 72 hours (separated by at least five days) during which they were given one of the four dietary interventions. The order of the diets was randomised across each study visit.

Adherence to the interventions was closely monitored with food weighed immediately before and after being given to the participants. Additionally, participants were only allowed to engage in very light physical activity – this was also closely monitored.

During the inpatient stay, urine was collected three times every day: morning collection (0900-1300h), afternoon collection (1300-1800h), and an evening and overnight collection (1800-0900h).

Of the 20 participants, 19 completed the full trial and their urine samples were assessed for metabolic profiles using proton nuclear magnetic resonance (1H-NMR) spectroscopy. This is a process to analyse the chemical compositions of a substance.

What were the basic results?

Overall, the urine metabolic profiles were distinct enough to assess each of the diets consumed. The metabolite concentrations translated to specific components of each diet.

The results were interesting, for example, the 1H-NMR analysis showed that the presence of 19 metabolites were in significantly higher concentrations after consumption of diet 1 – which had the greatest agreement with WHO dietary recommendations – compared to diet 4 – the highest risk diet with the least agreement to recommendations.

The analysis also showed detailed variability in metabolite concentrations between the participants.

How did the researchers interpret the results?

The researchers concluded: "Urinary metabolite models developed in a highly controlled environment can classify groups of free living people into consumers of diets associated with lower or higher non-communicable disease risk on the basis of multivariate metabolite patterns.

"This approach enables objective monitoring of dietary patterns in population settings and enhances the validity of dietary reporting."

Conclusion

This well-designed, randomised crossover trial investigated whether the dietary intake in individuals could be revealed and measured using urine samples and found that it is possible.

Urine analysis using 1H-NMR spectroscopy was distinct enough to distinguish "healthier" and higher risk diets by looking at the metabolites present in the urine.

The researchers hope that this study offers a method which could be used to assess adherence to healthy eating programmes, and potentially be used as a screening tool to identify and monitor individuals at risk of obesity and non-communicable diseases.

These tests have the potential to be of benefit as a research tool. Some studies have suggested that as many as 88% of people record their dietary intake inaccurately, so an independent objective measuring tool, could be very helpful.

Although this study sounds promising, the study sample was small with only 19 participants completing the full trial. Even in the context of a crossover trial this is very small and may not give reliable enough results from which to draw firm conclusions.

Further research with a much larger sample size may be required to see that urine metabolite testing is accurate enough to distinguish dietary patterns and then be used by researchers and health services.

If you are trying to improve your diet, and possibly lose weight, then following the NHS Choices Weight Loss Plan may help. This provides downloadable "diet diary" sheets as well as suggestions for healthy meal choices.