A team led by Elaine Holmes and Ruey Leng Loo of Imperial College London took advantage of an older epidemiological study on diet and blood pressure that collected urine samples from 4,680 people between 1997 and 1999. These samples were analysed, and the results published in 2003, then preserved with boric acid and kept frozen. The research team were able to do with most of the samples something not possible in the original study: identify all the chemical compounds in the urine, using an analytical technique called proton nuclear magnetic resonance spectroscopy. The method produces a graph with thousands of peaks, each of which corresponds to a different metabolite, the compounds left over after the body is done digesting food. The researchers then compared these graphs across the 17 populations of subjects, who came from China, Japan, the United Kingdom and the United States. “Of the thousands of peaks, we find the 20, 30 or 40 that are different” from each other, says team member Jeremy Nicholson, also from Imperial College.
“What our study really shows is how incredibly metabolically diverse people are around the world,” says Nicholson. “British and American [metabolomes] are nearly identical. Japanese and Chinese people are totally different metabolically even though they are nearly identical genetically.” People who lived in Hawaii had metabolomes equally similar to those of people on the mainland United States and in Japan. Interestingly, Nicholson says, the biggest difference between the 17 groups was between people from South China and everyone else. “They have a very different and much broader range of diet,” he says. “Very broadly speaking, the southern Chinese are the healthiest and the people in southern Texas are least healthy.”