You are what you eat

A major weakness in all nutrition and diet studies is that we have no true measure of what people eat. We rely solely on people keeping logs of their daily diets – but studies suggest around 60 per cent of people misreport what they eat to some extent.

So although we have big data collections about diet and health, using patient log books, we don’t have very accurate information because of widespread misreporting. This can be for a variety of reasons, which include being too embarrassed to tell the truth or simply because it can be hard to record everything you eat and drink over days and weeks.

With this in mind, my team at Imperial alongside researchers from Newcastle University and Aberystwyth University decided to come up with an independent test that could reliably reveal the quality of a person’s diet. We started with a simple premise – asking 19 volunteers to come into a clinic for three days and then eat and drink very defined diets, ranging from very healthy to very unhealthy. These were formulated using World Health Organisation dietary guidelines, which advise on the best diets to prevent conditions such as obesity, diabetes and heart disease.

Throughout this three day period, we collected urine samples in the morning, afternoon and evening and then assessed the urine for hundreds of compounds, called metabolites, produced when certain foods are broken down in the body.

By analysing the thousands of metabolites in the volunteers’ urine, we were able to come up with an accurate test that measures biological markers in urine created by the breakdown of foods such as red meat, chicken, fish and fruit and vegetables. The analysis also gives an indication of how much fat, sugar, fibre and protein a person has eaten. We tested the accuracy of the test on data from a previous study. This included 225 UK volunteers as well as 66 people from Denmark.
All of the volunteers had provided urine samples, and kept information on their daily diets.

Analysis of these urine samples enabled us to accurately predict the diet of the 291 volunteers.

As a control, we developed a urine metabolite profile of a healthy, balanced diet with a good intake of fruit and vegetables. The idea is this ‘healthy diet’ profile could be compared to the diet profile from an individual’s urine, to provide an instant indicator of whether they are eating healthily.

We still have work to do to ensure that the test will be accurate on a greater number of individuals but we are confident that it will be available for use in clinical practice within two years. We estimate that it will cost around £20 per test and that results will be available within one or two days. The results could pinpoint if someone was not eating sufficient fruit and vegetables for example, or eating too many refined carbohydrates and fats.

In particular, it will be useful to help people get an accurate understanding of their own diets and how they could improve their nutrition. This will be helpful to people who have pre-existing conditions such as heart disease and diabetes, but also people who are overweight and obese and struggling to lose weight. As part of our research, we have developed a urine metabolite profile of a healthy, balanced diet with a good intake of fruit and vegetables. This ‘healthy diet’ profile could be compared to the diet profile from an individual’s urine, to provide an instant indicator of whether they are eating healthily.

The study, funded by the Medical Research Council and the National Institute for Health Research, was published in the journal Lancet Diabetes and Endocrinology and conducted at the MRC-NIHR National Phenome Centre.