Here's How Metabolism Varies Between Populations

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London : An unusual study of frozen urine samples has shed new light on the diversity of human metabolism across the globe, say researchers at Imperial College London.

Two researchers, Elaine Holmes and Ruey Leng Loo, set out to study who eats what, and how their unique internal microorganisms handle the input.

They took advantage of an older epidemiological study on diet and blood pressure that collected urine samples from 4,680 people between 1997 and 1999.

The urine samples were preserved with boric acid, and kept frozen, they revealed.

Using an analytical technique called proton nuclear magnetic resonance spectroscopy, the research team identified all the chemical compounds in the urine.

The method provided the researchers with a graph of thousands of peaks, each corresponding to a different metabolite, the compounds left over after the body is done digesting food.

The researchers then compared the graphs across the 17 populations of subjects—from China, Japan, the UK and the US.

"Of the thousands of peaks, we find the 20, 30 or 40 that are different (from each other)," Nature magazine quoted team member Jeremy Nicholson as saying.

He said that the new method was not only helpful in linking specific metabolites to specific diseases, but also in comparing the entire suite of metabolites, known as the metabolome, between groups.

"What our study really shows is how incredibly metabolically diverse people are around the world. British and American [metabolomes] are nearly identical. Japanese and Chinese people are totally different metabolically even though they are nearly identical genetically," says Nicholson.

The researchers observed that metabolomes of people who lived in Hawaii was equally similar to those amongst people on the mainland US and in Japan.

Nicholson revealed that the biggest difference amongst the 17 groups was between people from South China and everyone else.

"They have a very different and much broader range of diet. Very broadly speaking, the southern Chinese are the healthiest and the people in southern Texas are least healthy," he says.

The study also revealed some intriguing relationships between high blood pressure and several metabolites, including formate and hippurate.

Teri Manolio, who runs the office of population genomics at the National Human Genome Research Institute in Bethesda, Maryland, says that the study finally demonstrates the feasibility of screening many metabolomes at one time.

"It opens up a whole new avenue to looking at diet and microbes between populations. This could be the paradigm-setting study where people say that this is feasible and reproducible," she says.

According to her, the effect of gut microbes on health has been underestimated.

"It is what is in the gut and elsewhere that influences the way we process foods and respond to infection," she says.